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S o m e aspects of the functional morphology of the shell of infaunal bivalves (Mollusca)
Watters, George Thomas, Ph.D.
The Ohio State University, 1990
UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106 SOME ASPECTS OF
THE FUNCTIONAL MORPHOLOGY OF THE SHELL
OF INFAUNAL BIVALVES (MOLLUSCA)
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the Graduate
School of the Ohio State University
By
George Thomas Watters, B.S., M.S.
*****
The Ohio State University
1990
Dissertation Committee: Approved by
A.S. Gaunt
D.H. Stansbery
W.C. Sweet Advi ser Department of Zoology B.D. Valentine To my parents and my wife for putting up with it and my grandfather- for starting it all
i 1 ACKNOWLEDGMENTS
The idea for this study began 14 years ago, and many
people during that time have contri buted thoughts and
suggesti ons I am indebted to all of these friends, too
numerous to mention, but particularly to K. Borror, Dr, R.
Fe1tes, W . Kasson, and D r . M . Hoggarth for thei r insights
into this research. My committee, Drs. A. Gaunt, D.
Stansbery, W. Sweet, and B. Valentine, also offered their suggestions and criticisms. Dr. J. Crites also commented on an ear1y draft. Thi s thesi s mi ght never have been wri tten, and certainly would not have been in this final form, were
it not for the generous help of these people.
To my wife and all the relatives who gave me support and encouragement, without which I would have given up on this dubious venture, I also offer my thanks and love.
Dr. J. Rosewater (U. S. National Museum of Natural
History) and Dr. R. Turner (Museum of Comparative Zoology) ki ndly made the col 1ections in thei r care avai1 able to me.
This study has been supported by a Sigma Xi Grant-in-Aid of
Research, a scholarship from the National Capitol Shell
Club, and an Ohio State University Presidential Fellowship. VITA
February 28, 1953 ...... Born - Dayton, Ohio 1971 ...... Graduated, Beavercreek H i gh School, Ohio 1974...... B.S., University of Miami, Coral Gables, Florida 1973-1977 ...... Student Co-curator of molluscs, University of Miami, Coral Gables, F 1 or i da 1974-1976 ...... Enzymology technician, Papanicolaou Cancer Research Institute, Miami, FIori da 1978 ...... Field entomologist, University of Rhode Island, Kingston, Rhode Island 1979-1981...... Micropaleontologist, CLIMAP, University of Rhode Island, Narragansett, Rhode Island 1980 ...... M.S., University of Rhode Island, Kingston, Rhode Is land 1986...... Field malacologist, The Nature Conservancy, Columbus, Ohio 1987 ...... Ecological analyst, Division of Natural Areas and Preserves, Columbus, Ohi o 1987 ...... Field malacologist, Division of Wildlife, Columbus, Ohio 1988 ...... Field malacologist, Indiana Department of Natural Resources / U.S. Department of the Interior 1989 ...... Stream ecologist, Columbia Gas
i v PUBLICATIONS
Watters, G. T. 1981a. A note on the occurrence of Lithophaga (Leioso lenus) spatiosa (Carpenter, 1857 ) In the shell- plates of Acanthochitona hirudiniformis (Sowerby, 1832). VeTiger 24:77.
Watters, G. T. 1981b. Two new species of Acanthochitona from the New World (Polyplacophora: Cryptoplacidae). Nautilus 95:171-177, plates.
Watters, G. T. 1983. A new species of Caducifer (Monostiolum) from the western Atlantic (Buccinidae). Nautilus 97:125-128, plates.
Watters, G. T. 1986. A survey of the unionid molluscs of the Big Darby Creek System in Ohio. Final Report to The Nature Conservancy, 149 pp., plates, maps.
Stansbery, D. H., Stein, C. B., & G. T. Watters. 1986. The distribution and relative abundance of unionid mollusks in the vicinity of Appalachian Power Company’s Clinch River Plant at Carbo, Virginia (Clinch River miles 264- 270). Final Report to American Electric Power Company, 148 pp., plates, maps.
Watters, G. T. 1988. The naiad fauna of selected streams in Ohio. I. Stillwater River of Miami River. II. Stream systems of south central Ohio from the LittTe Miami River to the Hocking River, excluding the Scioto River proper. Final Report to the Division of wildlife, Ohio Department of Natural Resources, vi+440 pp.
Watters, G. T. 1988. A field-guide to the fresh-water mussels of Ohio. Prepared for the Division of wildlife, Ohio Department of Natural Resources, v+110 pp.
Watters, G. T. 1988. A survey of the freshwater mussels of the St. Joseph River system, with emphasis on the federally endangered White Cat’s Paw Pearly Mussel. Final Report to the Division of Fish and Wildlife, Indiana Department of Natural Resources, vi+127 pp.
Watters, G. T. & J. Finlay. 1989. A review of the western Atlantic buccinid genera Monostiolum Dali, 1904, and Bailya (Parabailya) new subgenus. Veliger 32:47-59, plates, map.
FIELDS OF STUDY
Major Field: Zoology
v TABLE OF CONTENTS
DEDICATION...... i i
ACKNOWLEDGMENTS...... i i i
VITA i v
LIST OF TABLES...... vii
LIST OF FIGURES...... viii
CHAPTER PAGE
I. INTRODUCTION...... 18
History of Molluscan Morphometries...... 23 The Theoretical Morphospace...... 25 The Paradigm Approach...... 26 Predicted Models of Shell Shape...... 27
II. METHODS AND MATERIALS...... 32
Taxa Used in the Study...... 32 Measurements and Derived Values...... 33
III. RESULTS...... 43
Comparison of Shell Shapes with Models...... 43 Family Accounts...... 48
IV. DISCUSSION...... 59
Underlying Assumptions and Models...... 59 Evolutionary Considerations...... 72
SUMMARY...... 76
APPENDICES
A. Taxa Used In Study...... 204
B. Calculated Values of Parameters...... 218
LIST OF REFERENCES...... 232 vi LIST OF TABLES
TABLE PAGE
1. Di stri bution of representatives ofthe bivalve families used in study in each of the three morphological phases...... 203
2. Taxa used in study...... 205
3. Calculated values for the taxa used in this study...... 219
vii LIST OF FIGURES
FIGURES PAGE
1. Measurements taken from taxa in Appendix A ...... 35
2. Bivalve interpreted as a rectangular solid of length L t width W t and height H ...... 39
3. Relationship between quasi-streamlining (S) and the offset angle between the line of greatest length and the direction of motion...... 4.1
4. Diagrammatic representation of exchangeable gapage and rocking along a dorso-ventral axis....65
5. Rotation of the valves along the hinge axis (HA)...... 67
6. Rotation of the valves along a dynamic dorso- ventral ax i s ...... 69
7. Anterior and posterior adductor moments for Tresus nuttaJi...... 70
8. Adductor moment lines for Tagelus divisus through entire angle of exchangeable gape rocking movement...... 70
9. Adductor moment lines for Resartia lancaolata through entire angle of exchangeable gape rocking movement...... 71
10. Adductor moment lines for Siliqua patula through entire angle of exchangeable gape rocking movement...... 71
11. Plot of relative permanent gapage (P) and quasi-streaml i ni ng (S) for all species...... 80
12. Plot of morphospace occupied by studied taxa for relative permanent gapage (P) and quasi - streaml ining (S )...... 81
vi i i 13. Inferred sequence of morphologies for relative permanent gapage (P) and quasi-streamlining (S)...... 82
14. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Cardiidae...... 83
15. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Veneridae...... 84
16. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Mactridae...... 85
17. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Tellinidae and Donac i dae...... 86
18. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Psammobiinae and Sangui nolariinae...... 87
19. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Solenacea...... 88
20. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Solecurtinae...... 89
21. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Myidae...... 90
22. Plots of relative permanent gapage (P) and quasi-streamlining (S) for Unionoida...... 91
23. Plot of relative permanent gapage (P) and relative exchangeable gapage (E) for all species...... 92
24. Plot of morphospace occupied by studied taxa for relative permanent gapage (P) and exchangeable gapage ( E )...... 93
25. Inferred sequence of morphologies for relative permanent gapage (P) and exchangeable gapage (E)...... 94
26. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Cardiidae...95
27. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Veneridae...96
i x 28. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Mactridae...97
29. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Tellinidae and Donacidae...... 98
30. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Psammobiinae and Sangu i nol ar i i nae...... 99
31. PIots of re 1 at i ve permanent gapage (P ) and relative exchangeable gapage (E) for Solenacea..100
32. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Solecurtinae...... 101
33. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Myidae 102
34. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Unionoida..103
35. Plot of relative permanent gapage (P) and relative position of umbo (U) for all species... 104
36. Plot of morphospace occupied by studied taxa for relative permanent gapage (P) and relative position of umbo (U)...... 105
37. Inferred sequence of morphologies for re 1ative permanent gapage (P) and relative position of umbo (U )...... 1 06
38. Plots of relative permanent gapage (P) and relative position of umbo (U) for Cardiidae 107
39. Plots of relative permanent gapage (P) and relative position of umbo (U) for Veneridae 108
40. Plots of relative permanent gapage (P) and relative position of umbo (U) for Mactridae 109
41. Plots of relative permanent gapage (P) and relative position of umbo (U) for Tellinidae and Donacidae...... 110
42. Plots of relative permanent gapage (P) and relative position of umbo (U) for Psammobiinae and Sanguinolari inae...... ill
x 43. Plots of relative permanent gapage (P) and relative position of umbo (U) for Solenacea...... 112
44. Plots of relative permanent gapage (P) and relative position of umbo (U) for Solecurtinae..113
45. Plots of relative permanent gapage (P) and relative position of umbo (U) for Myidae...... 114
46. Plots of relative permanent gapage (P) and relative position of umbo (U) for Unionoida... 115
47. PIot of relative permanent gapage {P ) and relative depth of sinus (N) for all species..... 116
48. Plot of morphospace occupied by studied taxa for relative permanent gapage (P) and relative position of sinus (N)...... 117
49. Inferred sequence of morphologies for relative permanent gapage (P) and relative position of si nus (N)...... 118
50. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Cardiidae...... 119
51. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Veneridae...... 120
52. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Mactridae...... 121
53. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Tellinidae and Donac i dae...... 122
54. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Psammobiinae and Sangui nolar i i nae...... 123
55. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Solenacea...... 124
56. Plots of relative permanent gapage (P) and relative depth of sinus {N ) for Solecurtinae.... 125
57. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Myidae...... 126
58. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Unionoida...... 127
xi 59. Plot of relative exchangeable gapage (E) and quasi-streamlining (S) for all species...... 126
60. Plot of morphospace occupied by studied taxa for relative exchangeable gapage (E) and quasi stream 1 ining (S)...... 129
61. Inferred sequence of morphologies for relative exchangeable gapage (E) and quasi-streamlining ( S)...... 1 30
62. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Cardiidae...... 131
63. PIots of relati ve exchangeable gapage (E ) and quasi-streamlining (S) for Veneridae...... 132
64. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Mactridae...... 133
65. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Tellinidae and Donacidae...... 1 34
66. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Psammobiinae and Sangui nol ar i i nae...... 135
67. Plots of relative exchangeable gapage (E) and quas i-streaml i n i ng (S) for Solenacea...... 136
68. Plots of relative exchangeable gapage (E) and quasi-streaml i ni ng (S) for Solecurtinae...... 137
69. Plots of relative exchangeable gapage (E) and quasi-streaml ining (S) for Myidae...... 138
70. Plots of relative exchangeable gapage (E) and quasi-streaml i ni ng (S) for Unionoida...... 139
71. Plot of relative exchangeable gapage (E) and relative depth of sinus (N) for all species 140
72. Plot of morphospace occupied by studied taxa for relative exchangeable gapage (E) and relative depth of sinus (N)...... 141
73. Inferred sequence of morphospace for relative exchangeable gapage (E ) and relative depth of si nus ( N)...... 142
x i i 74. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Cardiidae...... 143
75. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Veneridae...... 144
76. Plots of relative exchangeable gapage (E) and re 1 at i ve depth of si nus (N ) for Mactri dae...... 145
77. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Tellinidae and Donac i dae...... 1 46
78. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Psammobiinae and Sangui nol ar i i nae...... 147
79. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Solenacea...... 148
80. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Solecurtinae.... 149
81. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Myidae...... 150
82. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Unionoida...... 151
83. Plot of quasi-streamlining (S) and relative position of umbo (U) for all species...... 152
84. Plot of morphospace occupied by studied taxa for quasi-streamlining (S) and relative position of umbo (U)...... 153
85. Inferred sequence morphologies for quasi-streamlining (S) and relative position of umbo (U )...... 154
86. PIots of relati ve posi ti on quasi-streamli ni ng CS) and relative position of umbo (U) for Cardi idae...... 1 55
87. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Vener i dae...... 156
88. Plots of relati ve pos i ti on quasi-streamli ni ng (S) and relative position of umbo (U) for Mactri dae...... 157
xi i i 89. PIots of relative posi tion quasi-streamlining (S) and relative position of umbo (U) for Tellinidae and Donacidae...... 158
90. PIots of relative position quasi-streamlining (S) and relative position of umbo (U) for Psammobiinae and Sangui nol ari i nae...... 159
91. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Solenacea...... 1 60
92. Plots of relative position quasi-streamlining (S ) and relative position of umbo (U) for Solecurtinae...... 161
93. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for My i dae...... 162
94. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Uni onoi da ...... 163
95. Plot of relative exchangeable gapage ( and relative position of the umbo (U) for a species...... 1 64
96. Plot of morphospace occupied by studied taxa for exchangeable gapage (E) and relative position of umbo (U)...... 165
97. Inferred sequence of morphologies for exchangeable gapage (E) and relative position of umbo (U )...... 166
98. Plots of relative exchangeable gapage (E) and relative position of umbo (u) for Cardiidae 167
99. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Veneridae 168
100. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Mactridae 169
101. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Tellinidae and Donaci dae...... 170
102. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Psammobiinae and Sangui nol ari i nae...... 171
xi v 103. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Solenacea 172
104. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Solecurtinae..173
105. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Myidae...... 174
106. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Unionoida 175
107. Plot of relative position of umbo (U) and relative depth of sinus (N) for all species 176
108. Plot of morphospace occupied by studied taxa for relative position of umbo (U ) and relative depth of sinus (N)...... 177
109. Inferred sequence of morphologies for relative position of umbo (U) and relative depth of sinus (N)...... 178
110. Plots of relative position of umbo (U) and relative depth of sinus (N) for Cardiidae...... 179
111. Plots of relative position of umbo (U) and relative depth of sinus (N) for Veneridae...... 180
112. Plots of relati ve pos i ti on of umbo (U ) and relative depth of sinus (N) for Mactridae...... 181
113. Plots of relative position of umbo (U) and relative depth of sinus (N) for Tellinidae and Donacidae...... 182
114. Plots of relative position of umbo (U) and relative depth of sinus (N) for Psammobiinae and Sangui nol ari i nae...... 183
115. Plots of relative position of umbo (U) and relative depth of sinus (N) for Solenacea...... 184
116. PIots of re1 at i ve posi t ion of umbo (U ) and relative depth of sinus (N) for Solecurtinae.... 185
117. Plots of relative position of umbo (U) and relative depth of sinus (N) for Myidae...... 186
118. Plots of relative position of umbo (U) and relative depth of sinus (N) for Unionoida...... 187
xv Plot of quasi-streaml1ning (S) and relative depth of sinus (N) for all species...... 168
Plot of morphospace occupied by studied taxa for quasi-streamlining < S) and relative depth of sinus (N)...... 189
Inferred sequence of morphologies for quasi-streamlining (S) and relative depth of si nus (N )...... 1 90
Plots of quas1-streamlining (S) and relative depth of sinus (N) for Cardiidae...... 191
Plots of quasi-streamlining (S) and relative depth of sinus (N) for Veneridae...... 192
PIots of quasi-streamlining (S) and relative depth of sinus (N) for Mactri dae...... 1 93
Plots of quasi-streamlining (S) and relative depth of sinus (N) for Tellinidae and Donaci dae...... 1 94
Plots of quasi-streamlining (S) and relative depth of si nus (N ) for Psammobi i nae and Sangui nolari i nae...... 195
PIots of quasi-streamlining (S ) and relat i ve depth of sinus (N) for Solenacea...... 1 96
Plots of quasi-streamli ni ng (S ) and relati ve depth of sinus (N) for Solecurtinae...... 197
Plots of quasi-streamlining (S) and relative depth of sinus (N) for Myidae...... 198
Plots of quasi-streamlining (S) and relative depth of sinus (N) for Unionoida...... 199
Frequency of the relative position of the umbo in the taxa studied...... 200
Frequency of the relative depth of the sinus in the taxa studied...... 200
Frequency of quasi-streamlining in the taxa studied...... 201
Frequency of exchangeable gapage in the taxa studied...... 201
xv i 135. Frequency of permanent gapage in the taxa stud i ed ...... 202
136. Frequency of the three phases predicted by the model...... 202
xvi i CHAPTER I
INTRODUCTION
The class Bivalvia of the phylum Mollusca appears to be
the single most diverse group of organisms extant that have
radiated principally into the deep infaunal zone.
Nevertheless, the fossil record indicates that this
colonization required nearly 200 million years to become
widespread, despite the fact that the earliest known
representatives of the class were shallow infaunal
burrowers.
The deep infaunal habitat has several potentially
positive adaptive features. Predation is reduced because of
the general lack of burrowing molluscivores. The sediment
acts as a buffer, ameliorating thermal, salinity, pH, and other environmental extremes. Desiccation is minimized. For these reasons, this habitat has certain advantages to an organism associated with this life style.
Why did it take so long, and why did so few members of the Bivalvia colonize the deep infaunal zone? It is probable that the changes required in evolving into the deep infaunal zone involve such considerable morphological modifications that members of few lineages have survived or ever began the
18 1 9 transition. The acquisition of characteristics that allow the bivalve to burrow in the substrate to greater depths must have occurred by degrees. Each modification was either adaptively or neutrally selective. Such intermediate morphological steps would have had their own immediate selective advantage.
The acquisition of shell structures and behaviors assoc i ated wi th deep burrowi ng has occurred in relatively few members of the bivalve families. This implies that characteristics that made for survival in this habitat served some other function in some other habitat, and that these particular characteristics were selected by natural factors or processes that resulted in deep burial. Members of lineages lacking these prerequisite characteristics could not attain a deep infaunal existence. These characteristics include the anatomy of the living individual, behavior, and the shape of the shell. This study is limited to a consideration of the shell.
It is here hypothesi zed that bi valves assoc i ated wi th the deep infaunal habitat should have a similar shell shape if there exists a suite of characteristics necessary to ach i eve thi s type of ex i stence. The presence of homeoplasy
(similar shell shapes by convergence, parallelism, or iteration) by individuals of deep infaunal species across suprageneric taxonomic levels would support this hypothesis.
This study proposes to obtain measures of shell shape 20
describing differences that may arise in a transition from a
shallow to a deep infaunal existence. These measures are:
1) degree of quasi-stream] ini ng. This is a measure of the amount of surface area of the shell that is oriented perpendicular to the long axis of shell.
2) relative position of the umbo. The placement of the umbo on the she!1, standard i zed to remove size effects.
3) relative depth of the pallial sinus. The depth of the pallial sinus, standardized to remove size effects.
4) amount of permanent gape. The sum of the anteri or and posterior gapes in the commissure of the shell that cannot be closed by rocking the shells along a dorso-ventral axis.
5) amount of exchangeable gape. The amount of gape created by rocking the she11s along a dorso-ventral axis minus the amount of permanent gape.
These parameters are discussed in detail under "Methods.”
The hypothesis just proposed may be extended to include bivalve shell shape at any point between shallow and deep burrowing forms. Restated, the hypothesis may be expressed in the following manner. Shell shapes form a predictable sequence among individuals that inhabit the shallow to deep infaunal habitats because a necessary suite of shell characteristics is needed to succeed in a deep infaunal habitat. This sequence is defined by the pairwise distribution of each of the measurements specified in the preceding paragraph for representatives of the species in 21
thi s study. The existence of such a sequence could explain
the rarity of deep infaunal bivalves and the degree of
homeoplasy present in burrowing bivalves in general. It may
be that few Recent representatives of bivalve lineages are
deep infaunal burrowers because ancestral members of the
1i neage 1acked the shel1 characteristics necessary to
succeed in this habi tat.
The sequence may be divided into three phases. The
shallow infaunal phase contains bivalves that do not have
exchangeable gapage. The deep infaunal phase contains forms
wi th permanent gapage. These i ndi vi duals common1y are deep
burrowing or sedentary forms. The intermediate phase
connects the two previous phases. It contains forms having
exchangeable gapage. Homeoplasy would be the expected result
if only a few sequences of shell shape morphologies existed
among those individuals that occur in these phases.
It has long been known that there is convergence in
shell characteristics in bivalves. Seed (1980b:32) stated
that "perhaps one of the most stri ki ng features concern i ng
the evolution of such a diverse group as the bivalves has
been the repeated appearance of a comparatively restricted
number of very successful shell morphologies." Linnaeus,
Cuvier, Bruguifcre, and Lamarck placed bivalves in only a few
genera. They based their criteria for classification
primari ly upon shel 1 form and a consideration of hinge
dentition, but little internal anatomy. This is in contrast 22
to a recent classification (Vaught, 1989) that lists nearly
1000 genera. It is apparent that unrelated taxa may possess
similar shells when internal anatomy, dentition, and larval
types are also examined. This has been a major obstacle to
the study of fossil forms.
Two hypotheses may be formed to explain this
convergence. They are not mutually exclusive. The first
states that similar she 11s have ari sen i n response to
similar environmental pressures. Convergence has occurred
because of natural selection "favoring" a specific shell
shape.
However, evoluti on may act onl y upon avai1able morphological material. Pre-existing structures may be co opted for a different use or an improved original function
if the genetic program can be modified in such a fashion.
Th i s is the basi s behi nd the second hypothesi s of convergence in shel1 shapes. Bi valve shel1s may be si mi 1ar
because there is only a limited range of values for shell geometric parameters that occur in nature. Convergence may be expected as a result of this restriction if there are few viable alternative shell shapes.
The results of this study suggest that the cause of convergence in bi valve shel1 shape may be explained as the consequence of a sequence of morphologies. This sequence represents a compromise between natural selection and morphological constraints. Evolution is conditional and the 23
changes at any step in a phylogeny depend upon the
characteristics of the previous step. Such "trends'' have
been modeled satisfactorily by a Markov process or random
walk (Bookstein, 1987). As an example, Cope’s Law of
Phyletic Size Increase has been shown to be stochastic
(Stanley, 1973). The convergence of bivalve shell shapes may
be such a stochastic process.
History of Mol Tuscan Morphometries
The molluscan shell has long been recognized as a
geometric form, at least in the artistic sense. Examples of this geometry, as a by-product or necessity of biological design, were not popularized until D ’Arcy Thompson (1942) published "On Growth and Form." The study of shell geometry did not progress past this recognition stage for many years.
The computations were time consuming and the results difficult to visualize as three-dimensional shapes.
Geometric studies of this type have been facilitated by computers. Raup (1961, 1962, 1963, 1966, 1967) identified the basic parameters of spiral coiling and generated computer si mu1ati ons of mol 1uscan she 11s . He demonstrated that a simple gastropod or cephalopod shell design could be modeled wi th few var i ables. Recent1y , Savazz i ( 1987) has produced an even more realistic computer generated model.
The science of "theoretical morphology" (Raup & Michelson,
1965) and, more specifically, "conchy1iometry" (coined by
Naumann, 1840), became a discipline belonging as much, if 24
not more, to computer programmers and mathematicians as to
biologists. The course of these studies has culminated in
Bayer’s 1978, purely mathematical analysis of shell shape
using "morphogenetic programs." The emphasis of these
stud i es had shi fted from the bi ologi cal aspects of she 11
geometry to a consideration of the biometrics as the sole
purpose of the investigation.
In 1970, Stanley published a study of marine bivalves
that marked a turning point in molluscan morphometries. He
presented a synthesi s of shel1 geometry, systemati cs ,
ecology, and field observation. For the first time, on a
comprehensive scale, explanations were advanced for whv
shells were shaped like they were, rather than how they were
shaped. Following the studies of Trueman et al. (1966a) and
Nair & Ansel 1 (1968) on the dynamics of bivalve burrowing,
Stanley’s work showed that members of such diverse groups as
the solecurtines, the solenids, the cardiids, and the
mactrids had highly convergent shells because of similar
habitats. From his results I have inferred the possibility
of analogous, predictable shell shapes in equivalent niches
regard1 ess of phylogeneti c posi ti on .
Stanley ( 1969, 1970, 1972, 1975, 1977b, 1981 )
documented the probable function of many types of marine
bivalve sculpture. I believe that the single most important
conclusion of these works was the concept of "composite sculpture," the exaptation (sensu Gould & Vrba, 1982) of 25
pre-existing sculpture for vicarious multiple tasks. Gould
and Vrba coined this term for character i sti cs of ancestral
forms that have been co-opted for a new function. For
example, radial ribs may have originated as sculpture
strengthening the she 11 in individuals of the Cardiidae.
That sculpture has been sxapted to function as a burrowing
dev ice in many members of the trachycardiinine cockles. As
aspects of the function of shell sculpture have been
discussed elsewhere, they generally will not be addressed in
this study.
The Theoretical Morphospace
Of central importance to this analysis is the concept
of the theoretical morphospace. The theoretical morphospace
of an organism is the array of potential shapes that it may
possess. This space usually is limited to a few parameters,
such as size, coiling rate, or color, for experimental studies. It represents the possible range of values of that
parameter. The theoretical morphospace may be contrasted with the actual morphospace. The actual morphospace is the observed values of that parameter, or in a broader sense, the form in which the organism actually is found in nature.
The actual morphospace is always a subset of the theoretical morphospace. In its simplest form, this methodology addresses the question: Why are things shaped the way they are? Or converse1y , why aren’t they shaped 1 i ke something else? It is the latter question that may be the most 26
insightful, for it implies a limi tat ion of form and a
constraint on possible morphologies. The cause of this constraint may be fundamental to understanding the organism
in question. The i dea of the theoret i cal morphospace has been applied to the morphological features of several groups, most notably coiling in cephalopods (Raup, 1967),
Convergence is most apparent in a morphospace scenario.
Phy1ogenetical1y unrelated groups that consistently occupy the same morphospace have converged toward the same values of the morphospace parameters. In this study, the sum of overlapping regions is shown to 1 ie along a wel 1 defined sequence of shell shapes.
The Paradigm Approach
Rudwick (1965) is usually given credit for advancing the use of the paradigm approach in biology, although this method of analysis may have been in use for many years. The term is from the Greek paradei gma, meaning "example" or
"model." The methodology allows the worker to form hypotheses concerning the potential characteristics of an organism possessing a certain life style or behavior, given information on the necessities of the organism’s life and its general morphology. For example, given the morphological characteristics of a small dinosaur, what changes are necessary to metamorphose it into a bird? The result is a model having parameters describing the organism in that life style as dictated by the logic of the investigator and the 27 presumed efficiency of those characteristics. The value of
the model is in its degree of resemblance to the actual organism. What are the discrepancies, if any, and how are they significant?
The paradigm model is similar to the theoretical morphospace. Both analyses compare actual and hypothetical characteristics of an organism. The model represents a region of the theoretical morphospace that has a high probability of being the actual morphospace, based on outside inferences. Both form a consistent pattern against which to compare the results of analyses.
Predicted Models of Shell Shape
It is possible to predict sequences in the values of shel1-shape parameters using the paradigm methodology. These parameters may be taken as a whole to describe the overal1 shell shape. The models are understood most easily as pairwise comparisons of the parameters.
Permanent gapage and quasi-streamlining. Quasi - streamlining would be expected first to increase into the intermediate phase with increasing depth of burrowing, and then decrease as permanent gapage becomes pronounced.
Increased quasi-streamlining occurs as bivalves become more suited to burrowing in the shallow infaunal zone. At a critical depth, which varies from sediment to sediment and depends upon the size of the bivalve, the weight of the substrate limits the depth of burial. Deeper burrowing can 26
occur only by the formation of exchangeable gapage in a
lineage. This is the beginning of the intermediate phase.
The increasing degree of exchangeable gapage should begin to
diminish the amount of quasi-streamlining. As exchangeable
gapage is modified into permanent gapage, quasi-streamlining
should decrease continuously as the life style shifts from
efficiently moving in the shallow substrate to a deeply
buried sedentary existence.
Permanent gapage and exchangeable gapage. As with
quasi-streamlining, levels of exchangeable gapage should
rise and then fall with increasing permanent gapage and
deeper infaunal existence. The peak of exchangeable gapage
lies within the intermediate phase. Quasi-streamlining is modified into exchangeable gapage, which in turn is modified
into permanent gapage.
Permanent gapage and relative position of umbo. The mode 1 i ndi cates that the umbo, as a relati ve measure of the position of the cardinal teeth, should become centralized to allow maximum exchangeable gapage as a lineage enters the
intermedi ate phase. The posi t ion of the umbo in individuals past the intermediate phase may depend upon the type of life sty 1 e. The 1 ocat i on of the umbo may be uni mportant i n sedentary forms that 1 ack a functional foot and unable to rock the shell along a dorso-ventral axis; or the umbo may become placed anteriorly in tube dwelling forms, which have
large muscular feet, because of the umbo’s associated pedal 29 muscle insertions. Two paths are expected out of the
intermediate phase.
Permanent gapage and relative depth of sinus. As burrowing depth increases, so must the length of the siphons
in non-tube dwelling forms. This entails a compensating
increase in sinus depth. The depth of the sinus will be high within the intermediate phase. Two paths are predicted as the lineage passes into permanent gapage. Siphons may become long without a concomitant increase in sinus depth if they remain permanently exterior to the shell, as in of the
Myidae. The siphons of others may retract, necessitating a deep pallial sinus.
Exchangeable gapage and quasi-streamlining. Quasi- streamlining is expected to increase into the intermediate phase until exchangeable gapage becomes more evident. As exchangeable gapage is modified into permanent gapage, both exchangeable gapage and quasi-streamlining should decrease.
Thus, there should be both a path out and in along the exchangeable gapage ax i s.
Exchangeable gapage and relative depth of sinus. The model i nd i cates that the relati ve depth of the s i nus should be high as the i ntermediate phase, characterized by the amount of exchangeable gapage, i s entered. The amount of exchangeable gapage will decrease as it is modified into permanent gapage. Two paths are possible beyond the i ntermed i ate phase because the fate of the depth of the 30 sinus depends upon which of two life styles, sedentary or tube dwelling, becomes apparent in the lineage. The reasons why one behavior may be favored by natural selection over the other are not known.
Ouasi-stream 1 ining and relative position of umbo. The relat i ve pos i t i on of the umbo should become centrali zed for maximum exchangeable gapage as quasi-streamlining passes into the intermediate phase. As previously mentioned, the fate of the position of the umbo depends upon factors not accounted for in this model and two paths are expected out of the i ntermed i ate phase.
Exchangeable gapage and relative pos i tion of umbo. The model must have both out and in components along the exchangeable gapage axis because exchangeable gapage is expected f i rst to i ncrease and then decrease dur i ng a radiation into the deep infaunal zone. The umbo will initially be central. The exact position of the umbo in the permanent gapage phase is not predictable by this model because two paths are possible at this point.
Relative position of umbo and relative depth of sinus.
The model predicts that as the umbonal position approaches a central location, the sinus depth should increase. As permanent gapage becomes established, the two variables may each take two different paths. Four paths are expected: 1) anteriorly placed umbo and short siphons (tube dwellers); 2) anteriorly placed umbo and long siphons (active deep burrowers); 3) centrally placed umbo and short siphons
(morphological precursors of (1)); and 4) centrally placed
umbo and long siphons (sedentary forms).
Quasi-streamlining and relative depth of sinus. With
increasing quasi-streamlining, the relative depth of the sinus should increase into the intermediate phase. Past this point the sinus depth may remain constant or decrease. CHAPTER II
METHODS AND MATERIALS
TaxaUsed in the Study
Representatives of 592 species and subspecies of bivalves were used in this study. Specimens were acquired from the following repositories and collections: Museum of
Comparative Zoology, Cambridge, M A ; National Museum of
Natural History, Washington, D.C.; Ohio State University
Museum of Zoology, Columbus, O H ; and the author"s private collection. The identification of museum specimens was taken from col 1ecti on records, wi th the fol1owi ng excepti ons at
Ohio State. Individuals of southeastern United States in the genus ETJiptio, and a few members of other genera from that region, were identified by the author, as were all marine species from that collection. These identifications may not reflect the views of systematists at that institution. The higher systematic levels are taken from Vaught (1989). A list of the spec i es used in this study is gi ven i n Appendi x
A.
Members of 13 families were selected for study, representing the majority of the living infaunal bivalve groups. These families, and the number of species or
32 33
subspecie8 used in this study for each in parentheses, are:
Hactridae (41); Cardiidae (56); Myidae (6); Psammobiidae
(25); Solenidae (8); Cultellidae (9); Tellimdae (49);
Donacidae (18); Veneridae (103); Unionidae (276); Hyriidae
(16); Mycetopodidae (13); and Mutelidae (11). Other infaunal
bivalve groups were not included, for the following reasons.
Individuals of the anomalodesmaceans are too rare to obtain
a reasonable sample. The Arcidae, Mytilidae, and Pinnidae
have infaunal members, but most are sessile and byssate, and
thus fundamentally different from the free living infaunal
groups chosen for study. Members of other groups, such as
the Astartidae, are too homogeneous to warrant repetitive
measurements. Individuals of the Lucinidae are infaunal and
have a wide range of shell shapes, and members of many
species are common. However, it has been suggested that this
group is only distantly related to other bivalves, based
upon morphology and behavior (Allen, 1958). The differences
are sufficient to eliminate the lucinids from this study of
infaunal groups.
Measurements and Derived Values
The following measurements were taken on individuals
for each of the species in Appendix A. Derived values for each individual are given in Appendix B .
Length - the greatest length along an anterior-posterior
line (Fig. 1a). This line, usually parallel to the hinge
axis, was measured in millimeters with a ruler. 34
Height - the greatest dorsal-ventral height, perpendicular
to the line for length (Fig. 1a). This line commonly extended through the umbo and was measured in millimeters wi th a ru1er .
Width - the greatest lateral width, with both valves closed
(Fig. 1b). The parameter was measured in millimeters with cali pers.
Position of umbo - the distance from the anterior margin to the umbo, along the length line (Fig. 1a), measured in millimeters with a ruler.
Depth of pal Hal sinus - maximum depth of the sinus measured out to a curve that follows the pallial line (Fig. 1a). The parameter was measured in millimeters with a ruler.
Anterior permanent gape - the maximum width of any anterior space between the valves when the valves are closed and rocked forward, if possible (Fig. 1b). The parameter was measured in millimeters with a ruler.
Posterior permanent gape - the maximum width of any posterior space between the valves when the valves are closed and rocked backwards, if possible (Fig. 1b). The parameter was measured in millimeters with a ruler.
Anterior exchangeable gape - the total anterior gape is the maximum width of any space created anteriorly between the valves when the valves are rocked backwards (Fig. 1c). The anterior exchangeable gape is the total minus the permanent anterior gape. It was measured in millimeters with a ruler. 35
LENGTH UMBO
H X a Ul X
SINUS
PPG WIDTH PEG
APG AEG B D
Figure 1 . Measurements taken from taxa in Appendix A. a. internal view of a bivalve illustrating the measurements of length, height, umbo, and sinus; b. dorsal view of a bivalve illustrating the measurements of width, permanent anterior gape (APG), and permanent posterior gape (PPG); c. dorsal view of a bivalve illustrating the measurement of anterior exchangeable gape (AEG); d. dorsal view of a bivalve illustrating the measurement of posterior exchangeable gape (PEG). 36
Posterior exchangeable gape - the total posterior gape is
the maximum width of any space created posteriorly between
the valves when the valves are rocked forwards (Fig. id).
The posterior exchangeable gape is the total minus the
permanent posterior gape. it was measured in millimeters
wi th a ru1er .
The following derived values were calculated from the
above measurements.
Quasi-stream!ining (S) - a univariate estimation of the
relative amount of surface area exposed perpendicular to the
direction of maximum length. The algorithm was devised for
this study to permit the simple quantification of a
parameter that has been expressed historically as a multivariate construction. The metric has the following
qualities. It is dintension less, independent of size, and has
a finite range of values. Its derivation, characteristics, and application will be treated in detail.
Workers in bivalve morphometries have realized that some shells are more elongated than others and should offer
less resistance to the substrate in burrowing activities.
Stanley (1970) and subsequent authors (notably Morton, 1976) have attempted to illustrate this shape by graphing ratios of shell measurements against one another and delineating a region of the theoretical morphospace as ‘'streamlined." The difficulty with this approach is that it requires two dimensions to describe elongation. If one wishes to 37
investigate the relationships between elongation and any other parameter, one must use multivariate correlations.
This has not been attempted, except in the study of Thomas
(1975) on glycymerid bivalves.
Streamlining in a different sense has been mathematically defined and quantified by engineers working with fluid and aerodynamics. Several attempts have been made to treat organi sms i n the same manner as shi ps and pianes.
These studies generally focus on optimum shapes for maximum speed, or the reverse, maximum speeds given a certain shape.
One recent study calculated swimming speeds of extinct marine reptiles (Massare, 1988). She calculated the total drag on reptiles using an estimation of surface area, water velocity, density of the medium, and the Reynolds number (a function of body shape in lamellar or turbulent flow). Such an analysis is not applicable to bivalves burrowi ng through a mixed substrate.
It must be emphasized that the use of the term
"streamlined" by malacologists working with bivalves is not that of Massare. That expression is used here as a descriptive variable, crudely measuri ng onl y the relati ve amount of surface area normal to the long axis of the shell, generally coinciding with the direction of burrowing. It carries no connotation of, or resemblance to, fluid dynamic theory. Neither is it a dynamic value dependent on burrowing speed, current velocity, or substrate type. Although 38
univariate, the quantification of streamlining put forth in
this study is identical to the sense of that term used in describing bivalve shell shape by Trueman et aJ. (1966b),
Stanley (1970), Alexander (1974), Eagar (1974, 1978), Thomas
(1975), Horton (1976), and Seed (1980a,b). The quantity derived in this study will be termed "quasi-streamlining" to differentiate it from the usage of Massare,
The calculation of quasi-streamlining (S) in this study estimates the shell shape as a rectangular solid of dimensions Length x Width x Height (Fig. 2). The value of S
1 ies between two hypotheti cal limits, i nterpreted as the mi n imum and max i mum amount of quasi-streamlining for the rectangular model. At the theoretical minimum, Height and
Width equal a unit measure (Height and Width = 1), and
Length = 0. Movement is in the di rection of Length, perpendicular to Height and Width. The model resembles a sheet of paper moving perpendicular to the face of the page.
This is the minimum amount of quasi-streamlining. The theoreti cal maximum i s achieved when Length = 1 and Hei ght and Width both equal 0. This mode 1 resembles a 1 ine of no thickness moving parallel to itself. Bivalves lie between the two extremes. The calculation is dependent on the relationship between Length and the remaining descriptors.
This has the effect of standardizing data by removing any i nf1uence of Length. The equati on can be wri tten a s :
S = (Width/Length)(Height/Length)(Length/Length) (1) 39
H
W
Figure 2. Bivalve interpreted as a rectangular solid of length L, width W, and height H.
When Height and/or Width is very small relative to Length, S
approaches 0. Conversely, when Length is very small relative
to Height and/or Width, S approaches infinity (®). It is
possible to limit these theoretical boundaries by raising
the natural logarithm (e) to the exponent S and taking the
inverse. Removing the cancelled expression (Length/Length),
and raising e to the remaining parameters yields the equation: s _ e ((Height/Length)(Width/Length)) ^2 )
Now as Length/Height or Length/Width -> 0, S -> «, and as
Height/Length or Width/Length -> 0, S -> 1. Taking the
inverse of the function has the following effect. As
Length/Height or Length/Width -> 0, S -> 0; as Height/Length 40
or Width/Length -> 0, S -> 1. The equation has the final
form: S = i/(e<(Height x Width)/(Length)~2)^
The resulting parameter is independent of original size,
unitless, and ranges from a value of 0 for no quasi-
streamlining to a value of 1 for maximum quasi-streamlining.
Although the values resemble percentages, they are not. As S
is univariate, it may be compared with other morphometric
parameters without the necessity of multivariate analysis.
The function is rectilinear within the biological range of
its values. In this study, a maximum S of 0.99 was encountered in several members of the solenid genus Ensis; a minimum of 0.01 was found in individuals of the epifaunal cardiid Corculum cardissa. S is not rectilinear beyond these values.
The choice of length as the direction of motion was necessitated by the lack of knowledge of the actual life positions of the majority of bivalves used in this study.
The use of this metric is considered a normalizing method.
Arguments may be raised against its use based upon the well- known fact that maximum length does not always correspond to burrowing direction. This is particularly true of such groups as the lucinids, which are not treated here. This discrepancy between length and direction of movement exists primarily in individuals of very shallow infaunal species, that have a low S and no gapage. It can be shown that as S 41
9 D> c «
*3 9 (0 <*- »*- O IS •
0 .3 0.4 0.5 8 . 0 0.9 1.0
Quasi-streamlining
Figure 3. Relationship between quasi-streamlining (S) and the offset angle between the line of greatest length and the direction of motion. i ncreases, the angle of offset dimi ni shes, for the few species for which data are available (Fig. 3). Host of the species discussed here have a S value > 0.8. Thus, for the majority of the forms considered, the incongruity between length and direction of movement is minimal. Even at large offset angles the discrepancy is overestimated. The shells at this level of S are generally circular in outline, or nearly eo.
The line of greatest length is a secant through the shell outline, as would be the direction of movement. Both approximately would be equal in length. Height would differ little between the two lines, and Width not at all. The 42
calculation of S may therefore be accurate even at low
levels of S.
Relative position of umbo (U) - the measurement of the
position of the umbo was divided by total length to
standardize this variable. The metric is a percentage of the
total length.
Relative depth of pallia1 sinus (N) - calculated as for U, using depth of pallial sinus.
Relative permanent gape (P) ~ standardized with the formula:
(4 )
(anterior permanent gape + posterior permanent gape)
2 x width
Relative exchangeable gape (E) - standardized with the formula:
(5)
(anterior exchangeable gape + posterior exchangeable gape)
2 x width CHAPTER III
RESULTS
Comparison of Shell Shapes With Models
Permanent gapage and quasi-streamlining. A comparison
with the results reveals that a1 though quasi-streamlining
initially does increase as permanent gapage increases, past
the intermediate phase the degree of quasi-streamlining
becomes constant rather than decreases in many individuals
(Figs. 11-13). There appear to be two paths out of the
intermediate phase, although the numbers of individuals in
that region are so few that it is difficult to make such a
claim with certainty (Figs. 14-22). Individuals of the
Tellinidae and Myidae conform to the predicted model given
above. Deep-burrowing forms have lost quasi-streamlining and may be sedentary as adults. Members of the solenaceans and of some solecurtines have maintained high levels of quasi
streamlining despite pronounced permanent gapage. This is
due in large part to the ability of many of these forms to
construct hollow burrows in which they move. The highest degree of quasi-streamlining is found in the tube dwelling members of Solen. Levels of permanent gapage and quasi- streaml ining are both high in these forms because these
4 3 44 bivalves no longer burrow through the substrate, but rather move within water filled tubes.
Permanent gapage and exchangeable gapage. The results support the model, and two paths are suggested (Figs. 23-
25). Members of the solenaceans and of some solecurtines occupy one path, but the individuals of the Myidae and other members of the Solecurtinae occur on the other path (Figs.
26-34). The first path contains forms having high levels of exchangeable gapage and permanent gapage as the result of their tube dwelling behavior. It is important to note that members of the Solecurtinae have participated in both paths, and that forms of the mactrids also appear to be diverging.
This suggests that members of a single family may not follow a single morphological path. This result occurs in several fami 1i es .
Permanent gapage and relative position of umbo. Two paths are evident out of the intermediate phase (Figs. 35-
37). The relative position of the umbo occurs between approximately 0.25 and 0.55 in this phase. The model predicts 0.5 for maximum exchangeable gapage, but most bivalves have the umbos placed anteriorly to act as a source of attachment and a buttress for pedal muse 1es. The intermediate phase average relative position of the umbo is approximately 0.4. From that point (and perhaps before), the umbo may be placed either anteriorly or slightly posterior 1y . The forms with anteriorly positioned umbos are 45
those that use the foot either as an anchor (Unionoida) or a
wedge within a burrow (solenaceans), not as a device for
active burrowing. The second path tends toward the
theoretical value of 0.5 and indicates an emphasis on active
burrowing and exchangeable gapage in most of its members
(Tellinidae, Solecurtinae, and others). The families
Cardiidae and Mactridae have forms that move in both
di rections.
Permanent gapage and relative depth of sinus. The
results suggest two routes away from the intermediate phase:
one toward slightly increased sinus depth and the other
toward greatly reduced depth (Figs. 47-49), Within members of a family, both paths may be found (Solecurtinae,
Tellinidae, and Mactridae; Figs. 50-58). Members of the solenaceans have reduced the sinus to a minimum despite their deep-infaunal habitat. This is due to a reduction in siphon length. Individual solenaceans 1 ive in water fi1 led tubes and may dwel1 at the surface, retreati ng to the bottom of the burrow only to escape danger.
Exchangeable gapage and quasi-streamlining. Quasi- streaml ining is expected to increase into the intermediate phase as exchangeable gapage becomes more evident. The results support this prediction (Figs. 59-61). Members of all families lie within a fairly narrow region of the theoretical morphospace. This is unexpected in view of the original prediction: as exchangeable gapage is exapted into 46 permanent gapage, both exchangeable gapage and quasi- streaml i ni ng should decrease. Thus, there should be a path out and in. That onl y a si ngl e course i s apparent has an important consequence for this study. Morphological constrai nts may i mpose such limits that sequences i n the values of parameters may reverse themselves and follow the same path back. Thus we find members of the Myidae in the same regi on as those of the Cardiidae. Among the solenaceans, the highly streamlined individuals of Ensis occur to the left of members of Silicjua, a genus in the intermediate phase (Figs. 62-70).
Exchangeable gapage and relative depth of sinus. The graphs in Figures 71-73 have an in component as well as an out, as predicted. From the relationship of permanent gapage to relative depth of the sinus, we know that two paths are evident out of the intermediate phase, either reduction or slight increase in sinus depth. The graphs illustrate two paths, each with an in and out section, all superimposed.
Although a vague pattern is suggested, the data cannot be separated into their discrete paths (Figs. 74-83).
Streamlining and relative position of umbo. Two paths are apparent out of the intermediate phase (Figs. 83-85).
The first is toward a slightly more posterior position and contains members of the Tellinidae, Psammobiinae,
Solecurtinae, and Myidae. The second, toward a more anterior placement, contains forms of the solenaceans and the 47
Unionoida. The Mactridae and Veneridae have members in both paths (Figs. 66-94).
Exchangeable gapage and relative position of umbo. The model predicts both out and in components (Figs. 95-97). The relati ve posi ti on of the umbo also may take two paths out of the intermediate phase. The path to the anterior placement of the umbo, as found i n forms of the solenaceans, has a loop out to a high level of exchangeable gapage from a central umbonal location, and back to a low level of both exchangeable gapage and umbonal position. The path to a posterior placement is not as well indicated but presumably
1 oops out for a much shorter di stance (0.15) on the exchangeable gapage axis before returning to a higher level of umbonal position (Figs. 98-107).
Relati ve position of umbo and relative depth of sinus.
The model predicts that the sinus depth should increase as the umbonal position approaches a central location, with two paths available out of the intermediate phase. This is illustrated by the weak relationship shown in Figures 107-
109. The variables increase together, with member of the families occupying discrete areas of the morphospace (Figs.
110-118).
Ouas7-stream 7ining and relative depth of sinus. The relative depth of the sinus is predicted to increase into the intermediate phase. Two paths are possible beyond the intermediate phase. This pattern is supported by the results 48
(Figs. 119-121), but there is also an unexpected result.
Members of the Unionoida do not participate in this path but reach a high level of quasi-streamlining with no appreciable sinus (or siphons; Figs. 122-130).
The presence of individuals of the Myidae so far back on the path suggests that the sequence is reversible along its path. This same result was found in the relationship between quasi-streamlining and exchangeable gapage.
Fami1v Accounts
Cardiidae. The cockles are a large family of shallow infaunal dwellers. As a group, they are sculptured heavily and the sculpture has been shown to be composite. Anti- scouring, anchoring, and burrowing sculptures may exist in the same species (Stanley, 1981). These sculptural devices are suited particularly to a shallow infaunal existence. Few members have colonized the deeper infaunal zone.
However, three of the five subfamilies have members that have entered the intermediate phase. None has evolved beyond. In the Protocardiinae, which contains the most primitive living cockles, members of Lophocardium have entered the intermediate phase. This is a rarely encountered deep-water group of perhaps three species. The
Laevicardiinae contains intermediate-phase members in
Fulvia. This genus is also composed of very few species
(Fischer-Piette [1977] placed this genus in the
Trachycardiinae, an allocation that is not followed here). 49
The Trachycardiinae includes the Papyridea, which contains
seven or eight species.
The premier examples of a group in the intermediate phase are members of the cardiid Papyridea. One must know
something about their ancestral stock to appreciate their
remarkable modifications. Papyridea is a genus of the trachycardi im n e cockles, which is a widespread and diverse group of tropical and sub-temperate species. Members of the subfamily are characterized by: 1) strongly radially ribbed shells, ornamented with complex composite sculptures used for burrowing and anti-scouring (Stanley, 1981); 2) short siphons, which limit them to a shallow infaunal existence;
3) umbos that are central , or nearly so; and 4) a short hinge plate with simple interlocking lateral teeth and centrally located cardinals. The pronounced ribs apparently act as strengthening devices and on the shell margin tend to interdigitate to form a "ventral hinge" (Carter, 1968).
Members of Papyridea have shell characteristics modified into features predicted for exchangeable gapage.
The dorso-ventral axis of shell rocking employs the following changes: 1) the central umbo and cardinal teeth become the static dorsal pivot; 2) the interdigitation of the ribs on the ventral margin becomes a dynamic pivot as the sculpture functions like the teeth on two intermeshed gears; and 3) the lateral teeth disengage in the resting position, but alternately mesh as the shells are rocked along the dorso-ventral axis. The shell has become more streamlined (S=0.74) than the majority of other cockle shells. The ribbed sculpture is minimized on the disc of the shell, although the composite sculpture is retained. The ligament is shortened and positioned near the umbo where it does not in ter fere with the rocking movements. The short siphons have become more elongate (Stanley, 1970). Unlike the shallow infaunal habitat of other members of the
Trachycardiinae, members of PapyriPea are known to burrow to approximately one half of their length and are moderately rapid burrowers. Stanley (1970:158) stated that an individual of P. soleniformis "has longer siphons and lives at a greater depth than other cardiids studied."
It is apparent that members of Papyridea are in the process of colonizing the deeper infaunal habitat. It is one of the few modern groups in the intermediate phase. The majority of bivalves are either bottlenecked behind this position (including 99* of the members of the Cardiidae), or have advanced into the permanent gapage phase (members of the solenids, cultellids, and solecurtines). The distribution of the families included in this study in the three phases is shown in Table 1.
Members of Papyridea stand out from the few groups in the same level of transition because of their high degree of modification of pre-existing shell characteristics. The central position of the umbo, the short centralized 51 ligament, and the simple lateral teeth all are prerequisite to enter the intermediate phase. It must be emphasized that entry into this phase depends upon the chance alignment of several shell characteristics, hence the great number of shallow infaunal species bottlenecked behind this morphologi cal barri er .
Verier i dae. The true, or Venus, clams comprise the largest family of living bivalves. Ansell (1961) categorized individuals of this family as soft substrate-dwelling with few burrowing modifications. Venerids have successfully exploited the shallow infaunal zone with little invasion of the deeper infaunal zone. None has achieved a quasi streamlining coefficient greater than 0.9 or a permanent gapage of greater than 0.15. None have entered the intermediate phase. This is because venerids have not achieved the sui te of characteri sti cs necessary to enter that part of the sequence. Ansel 1 (1961:514) remarked that
"[in members of the genus Petnco7a], well developed hinge teeth and the long ligament make rocking movements of the shell valves...impossible." Yet the members of the family have already begun to diverge along the quasi- streamlining/re1 ative position of the umbo paths (Fig. 67).
Members of the Meretricinae tend toward a more central umbonal position. Individuals of the Tapetinae and some elements of the Pitarinae (forms in Macroca11ista) and the 52
Chioninae (members of Protothaca) are on the path toward an anteriorly positioned umbo.
Mactridae. The surf clams encompass more morphological forms than any other family in this study. The group contains venerid-like shallow infaunal forms as well as deep infaunal dwelling individuals reminiscent of some members of the solenaceans. Stanley (1972, 1977a) has pointed out the convergence in morphology of mactrids with that of individuals of other families such as the Myidae, Veneridae, and Te11inidae.
A unique shell design is prevalent in this family and has been modified for the intermediate phase. The ligament has been internalized and positioned beneath the umbo in a resilifer, where it serves as a fulcrum during rocking as well as providing the opening moment of the valves (Yonge,
1982). The result is a central ligament independent of quasi-streamlining (Seilacher, 1984) that offer little resistance to exchangeable gapage.
Two paths may be taken out of the intermediate phase.
Members of four genera have entered the intermediate phase and/or exceeded it into the area of permanent gapage. As in the Cardiidae, the species within each genus are very few in number. These groups are members of the lutrariinine genera
Lutraria and Psammophila, both of European seas, and the
Indo-Pacific zenatiinine genera Zenatia and Resania (Beu
[1966] places the latter in its own subfamily, the 53
Resaniinae). Members of Resania are on the path to a centrally located umbo. Members of the other three all lie on a path toward an anterior umbo (Figs. 40, 88). For the relative depth of the sinus, members of Lutraria and
Psammophila tend toward a deep sinus, while those of Resania and Zenatia approach a very shallow sinus reminiscent of that found in the solenaceans. For exchangeable gapage, individuals of Psammophila are on the path of the myids, wh i 1 e the members of the remai n i ng three genera are on the solenacean path.
Individuals of Lutraria and Tresus have a reduced foot
(Yonge 4 Allen, 1985), indicative of diminished burrowing ability. Members of Tresus may live at substrate depths of
50 cm, where they are sedentary as adults (Yonge, 1982).
Cotton (1961:297) gave this account of an Individual of
Lutraria rhynchaena Jonas, 1844, a species in intermediate phase (note the modifications for exchangeable gapage):
[It] burrows deeply in sandy mud...siphons
reaching upwards to the surface... The short
ligament allows considerable movement at the ends
without openi ng the she 11 throughout. Wi th the
valves in their ordinary positions the shell gapes
equal 1 y at each end, but the arrangement of teeth
and ligament is such that the front of the shell
may be entirely closed. 54
That members of Lutraria lie on the solenacean path is not surprising. Beu (1966) described their life habits as tube dwelling in the manner of individuals of Solen.
Beu (1966) also noted the exchangeable gapage of members of Resania and Zenatia. He believed the former to be an active burrower in sand in the wave zone, and the latter to be a sedentary burrower offshore.
Lineages of the mactrids appear to be evolving (in the sense of the variables studied here) in diverse directions, more so than any other f ami 1 y covered in thi s study. The family has members in all possible paths and in all three morphologi cal phases.
Tellinidae. The tellins are a large group of active, quasi-streamlined bivalves that burrow to moderate depths.
Most have unsculptured shells, and the few groups with sculptured shells (some members of Scutarcopagia and
Strigilla, for example) have composite burrowing sculptures.
They are within the intermediate phase and appear to be on the path of the myids. They have extensive siphons and a pronounced sinus, as well as a central umbo, and the shell of many forms has some degree of exchangeable gapage.
Members of a few species can burrow to moderate depths
(Hughes, 1 969 ).
Yonge (1949) believed that forms of the Tellinidae,
Solecurtinae, and Donacidae were derived independently from members of the Psammobiinae resembling individuals of Gari. 55
Pohlo (1982) offered a different phylogeny, in which the
Tellinidae are at. the end of the sequence Donacidae ->
Solecurtinae -> Psammobiinae -> Tellinidae. The present study does not support this contention, and suggests a phylogeny more similar to that proposed by Yonge. Members of the donacids may be an offshoot of the tell ins specialized to the high-energy environment of the sandy intertidal zone.
The tell ins, as well as some forms of the psammobiids, have a unique "X "- shaped muscle, the cruei form muscle, that connects the ventral margins of the shells. Yonge (1949) noted that this muscle occurs at the ventral base of the si phonal attachment and suggested that it functioned to anchor the siphons at this margin during protraction and retraction. This muscle group could also serve as a ventral connection during a rocking motion which limited the ventral pivot to a specific point. This differs from the dynamic ventral pivot of most other groups in the intermediate phase.
Psammobiinas and Sanguinolari inae (Psammobi idae).
Members of these subfami 1ies are the morpholog i cal precursors of the solecurtine psammobiids, and occupy the intermediate phase for this family. They are morphologically the analog of the tell ins. But unlike them, members of the
Psammobiidae have a permanent-gapage group, the
Solecurtinae. Members of the family lie on the myid path. Solecurtinae (Psammobiidae). Individuals of this subfamily are a fairly small group that resemble the razor cl ams i n many shel1 characteristics. Members of the
Solecurtinae, with the exception of forms of Tagelus, do not construct tube-like burrows and have extensive siphons (and deep sinuses). Members of Tagelus are similar ecologically and behaviorally to the solenaceans (Stanley, 1970) and they occupy many of the same paths. The major difference is the position of the umbos, which are central in members of
Tagelus and anterior in solenaceans. Other groups of solecurti nes are on di fferent morpholog i cal paths.
So lenaceans. The razor clams have di verged from the majori ty of infaunal bivalves in behavior and habi tat. They construct tube burrows in which they move horizontally.
This habit has produced a d i sti net alternate path out of the intermediate phase. Siphons and sinus may be greatly reduced because the animal may dwell at the surface but become deep infaunal in the sense of this study only to avoid danger.
Because they can retreat i nto the deep substrate, permanent gapage is available. As tube dwellers, the highly streamlined shape is retained at maximum permanent gapage.
This combination of characteristics has led to two paths out of the post-intermediate phase morphologies. Yonge
(1951c:429) recognized the important principle that shell and soft anatomy are separate entities: "There is the fundamental, though largely unrecognized, fact that 57 throughout the Hollusca the growth of the body and the growth of the shell must be considered separately."
Myidae. The my ids are few in species number but quite variable in morphology and ecology. Members of the genus
Cryptomya live at depths of up to 50 cm, have only short siphons, and "tap" into the water filled cavities of burrowing crustaceans and echinoderms (Yonge, 1951a).
Members of Platyodon bore into soft stone (Yonge, 1951b).
These specializations aside, the members of the genus Mya illustrate the expected result of the modeled path. All exchangeable gapage has been modified into permanent gapage, quasi-streamlining is reduced, teeth are non-functional, and the sinus is shallow as the siphons become increasingly non- retractable. Like forms in the Mactridae, the myids have a central, internalized ligament carried within a resilifer
(Yonge, 1982). Analogs in the Hiatellidae (not included in this study), are individuals of Panopea, the geoduck clams.
Unionoida. Members of the four families of the freshwater unionoids participate in few of the paths discussed here. This seems to be attributable to their lack of fused mantle tissue, necessary to form siphons, without siphons, deep burrowing is not attainable unless tubes are constructed, as in the solenaceans. This behavior is unknown in members of the Unionoida. Although unionoids achieve a high level of quasi-streamlining, this type of shell form appears to function in quick reburial rather than efficient movement while buried. Individuals of the unionoids lie upon the solenacean path rather than upon the path of the other groups studied for quasi-streamlining and the relative position of the umbo. This is not to imply that unionoids are following the solenaceans in morphology. Unionoids have no siphons (with the possible exception of members of
Leila), cannot burrow far below the substrate/water level in most instances, and do not construct tubes.
Pholadacea. Although not used in this study, the shipworms and relatives are briefly discussed here because of their novel use of exchangeable gapage. The antero posterior rocking motion of the shells is used not only to protrude foot and siphons, but as a mechanical rasping device to excavate burrows in wood, shell, and stone. The shell and musculature have been reorganized to maximize this movement. These innovations have been discussed by Rbder
(1977) and Hoagland & Turner (1981). A recent study (Fuller et al., 1989) also documents the complicated ontogeny of individuals of one species of this group. CHAPTER IV
DISCUSSION
Underlying Assumptions and Paradigms
The fundamental assumption of this study is that there is a definite selective advantage to becoming deep infaunal.
The underlying question, then, is why aren’t there more deep infaunal bivalves? I conclude that the reason is related to the possible ways that a bivalve shell can be modified for this habitat. These modifications require a particular suite of characteristics. Only bivalves with this prerequisite suite can colonize the deep infaunal region. If the morphology of the 1 i neage cannot be modi f i ed , that group cannot succeed i n that habi tat. Entry i nto thi s sequence would be rare if there was little or no adaptive significance to the lineage possessing the suite, or if some other suite had high selective value. In the former case, the acquisition of the suite would depend on random fluctuations in the characteristics of the morphology. In the latter, there may be no impetus to move from one adaptive peak to another. A paucity of deep-dwelling forms would be the expected result if either of these factors occurred in the evolution of the bivalves. Convergence would
59 60 also be the expected result if only a few viable sequences of morphologies are available.
These constraints are due in part to the interactions between sediment and shell with increasing depth of burial.
For simplicity, I will consider the substrate to be homogeneous. The addition of heterogeneous and stratified sediment variables, while a much more realistic scenario, cannot adequately be accounted for in the context of this model. It is suggested that the simpler model may be extrapolated to the more complex.
The mechanics of burrowing in shallow infaunal bivalves have been documented by Trueman ( 1966), Trueman et al.
(1966a), and Stanley (1970, 1975). However, the members of all groups studied, such as Hercenaria mercenaria in Stanley
( 1975) have low S values, no exchangeable gape, and no permanent gape. The steps in burrowing in such forms may be given briefly:
1 ) The foot probes the substrate.
2) The siphons are closed.
3) Adductor muscles close the valves around the foot,
raising pressure in the haemocoel, which is transferred to the foot, forming an anchor.
4) Simultaneously, water is ejected from the mantle cavity, which momentarily loosens the immediately surroundi ng substrate. 61
5) The anterior pedal retractor contracts, pulling the
animal forward against the anchored foot.
6) The posterior pedal retractor contracts, returning
the shell to the original burrowing position.
7) The adductor muscles relax, diminishing haemocoel
pressure and redirecting fluid out of the anchored foot. The
siphons are opened.
This process continues until the animal is buried. Other
factors may also be i nvolved. Sculpture may assi st
burrowing, as may the presence of a prosogyre shape and a
lunule (Stanley, 1969, 1975, 1981). The focus of this study
is deep-dwelling bivalves. The burrowing model given above may work for only a small number of the groups considered in
this dissertation. The rocking motion around a dorso-ventral
axis becomes impossible as shells become more elongate (S
increasing; Stanley, 1970). The foot must protrude from the anterior gape and is often as large in cross-section as the
shell in quasi-streamlined shells. It appears, by its larger size, to be much stronger than the foot of shallow infaunal
burrowers of the same shell size. Eagar (1978) reported that the force of the pedal retractors may be equal to 100 times the weight of the shell in water in individuals of deep- dwelling Ensis, but equal to only one quarter the weight in members of shallow infaunal Mercenaria. These factors may be necessary in these groups to offset the lack of burrowing assistance that is found in shallow-dwelling forms afforded 62
by the rocking movement, shell sculpture, and lunule.
Expulsion of water to loosen sediment appears still to be
important. Many deep-dwelling forms have ventrally fused
mantle tissue that presumably directs water forward during a
burrowi ng cycle.
The ability to enter the substrate efficiently is a
function of shell shape. Nair & Ansel 1 (1968) found that
elongate shells offer the least resistance to burrowing. In
the context of this study, the design most suited to
burrowing is found in the entity having the highest S value,
all other factors being equal. This typically takes the form
of a laterally compressed, antero-posterior elongated blade
like shape. Sculpture is typically lost. Stanley (1970) has
shown that bivalves with coarsely sculptured shells are slow
burrowers. In a species with both infaunal and epifaunal
individuals, the infaunal morphs are more elongate (Seed,
1980a). Within.the same genus, deeply burrowing members are more quasi-streamli ned than are shal1 owly burrowi ng ones
(Alexander, 1974; Eagar, 1974), although Agrell (1949) has made a correlation between shell morphology and the trophic
level of the water body.
The sediment load pressure increases with increasing depth of burial (Nair & Ansel 1, 1968). This pressure would act to close the shells. The animal must exert a force to open the valves and keep them open (Stanley, 1970). In
bivalves this is accomplished typically by the ligament and/or haemocoel pressure. The valves must be opened to allow protrusion of the foot and siphons. Trueman et a/.
(1966a,b) have shown that the sediment pressure may exceed the opening moment of the ligament at critical depths, and that thi s effeeti vely 1i mi ts the depth of bur i al . One solution to this problem is the incorporation of permanent shell gapes in the morphology. The foot and siphons may be protruded through these openings or permanently left exposed. But the primary function of the shell is defense, and for thi s reason the vast majori ty of epi fauna1 or shallow infaunal forms have complete closure of the valves.
But a selective advantage is to be gained by penetrating the substrate further, including a concomitant loss of predators and an increase in habitat stability.
A solution to this problem requires having the shells retai n thei r functi on as protecti ve devi ces, while allowing the foot and siphons to protrude in a manner independent of the ligamental opening moment. Such a suite of characteristics does exist, and apparently represents the only compromise found in living bivalves. I have termed this unique morphology the intermediate phase, between the shallow- and deep-infaunal existence phases. It has a suite of predictable and testable characteristics that may be compared with actual forms.
The key innovation is exchangeable gapage (Fig. 4). The shells rotate along a dynamic dorso-ventral axis rather 6 4 than along th© dorsal hinge axis (Figs. 6, 6). Movement is affected by the adductor muscles rather than by the much weaker ligament or haemocoel pressure. Contraction of the anterior adductor muscle closes the anterior (pedal) gape and opens the posterior (siphonal) gape. Contraction of the posterior adductor muscle has the opposite effect. Several
important morphological requirements must be met for this mechan i sm to work.
First, the umbo must be approximate1y central. This orientation allows the maximum amount of exchangeable gapage at both ends. Second, the ligament must also be central and reduced. A long opisthodetic ligament would not allow rocking along a dorso-ventral axis. Third, cardinal teeth must be retained to act as the dorsal pivot of the axis.
Lateral teeth may or may not be present, but if present, they must be able to disengage smoothly as the rocking movement takes place. Fourth, the valve commissure must be open anterior and posterior, so as to create a gape when the shells are rocked.
Rocking along the dorso-ventral axis may have a adverse side effect. That is, simultaneous contraction of the adductor muscles may split the valves at the umbo along a line of structural weakness if the shell is sufficiently thin. This is known to happen in all members of the anomalodesmacean LaternuJa and some Pariploma (Morton,
1976). Individuals of other species, all within or past the 65
SIPHONAL GAPE
PEDAL GAPE
Figure 4. Diagrammatic representation of exchangeable gapage and rocking along a dorso-ventral axis. Top. Anterior adductor muscles contracted, creating si phonal gape posteriorly. Middle. No adductor muscles contracted. Note exchangeable gape at both ends. Bottom. Posterior adductor muscles contracted, creating pedal gape anteriorly. Each stage is illustrated by a dorsal and a lateral ^icw. Solid line marks dorso-ventral axis of rotation. X - fixed dorsal pivot at hinge line. 66
intermediate phase, may have an internal rib or buttress at
this position to counteract the stress: Nuculites
(Nuculidae); Capistrocardia (Saxicavidae); Cleidophorus
(Ledidae); Siliqua, Cultellus, and Phaxus (Solenacea);
Sanguinolaria, Nuttallia, Solecurtus, Pharus, and Tagelus
(Psammobiidae); and others (Gill & Darragh, 1964, and this
study). In other species, additional buttresses may be
present.
The presence and the position of these buttresses is
not simply the result of contracting adductor muscles during
normal closure (around the hinge axis). Factors influencing
the disposition of internal buttresses are tied to the
mechanics of exchangeable gapage. In most shells, the valves
rotate along an axis determined by the hinge line,
particularly the line through the ligament. The insertions
of the adductor muscles on the valves remain the same
distance from that axis throughout contraction and the
adductor muscles work in concert (Fig. 5). The situation is
different during exchangeable gapage. The dorsal pivot of
the axis is anchored, usually by the cardinal teeth. But the
ventral pivot moves along the ventral margin of the shell,
sweeping out an angle defined by the anterior and posterior-
most positions of the axis (Fig. 6). The distance from the adductor muscles to this dynamic axis changes in a linear
fashion during this rocking motion. The adductor muscles are
antagonistic during this motion. 67
HA
Figure 5. Rotation of the valves along the hinge axis (HA). The distance (1, 2) from the adductor muscles to the axis remains constant during closure.
Thomas (1975) estimated the amount of force generated during valve closure, the adductor moment, by:
(6 )
(cross-sectional area of adductor) x (distance to axis)
The cross-sectional area is an estimation of force. The distance to the axis represents the torque arm. In his calculations, which involved no exchangeable gapage, the adductor moments are constant during closure. The moments during exchangeable gapage are not, as illustrated in Figure
7. The 1 i nes of adductor moments may or may not cross, depending on the location of the adductor muscles and the shape of the shell. If the shell is thin, a buttress 66 generally will occur near the angle at which the moments are equal. This angle represents the point during an exchangeable gapage rocking motion that the anterior and posterior adductor forces are equal, thereby placing maximum strain on the shell between them if they are contracted simultaneously (Fig. 6). The buttress reinforces this region. Buttresses may also occur at the beginning and end of the exchangeable gapage angle. These may counteract the forces generated by the adductor muse 1es attempti ng to contract beyond the limit of the allowable angle. The central buttress may be placed at the bisection of the angle, but other evidence suggests that it appears to be dependent on the point of equal moments. For the individual in Figure 9, the lines do not cross and the central buttress is absent, although the two flanking ones limiting the angle are prominent. Figure 10 illustrates the moment lines for a form in which the lines cross only at the end of the angle.
The formation of internal buttresses appearsto be an mod i f i cati on for forces generated on the she11 by the adductor muscles during exchangeable gapage.
Past the intermediate phase, the deeply buried bivalve may take on equally predictable characteristics. Movement within the substrate is minimi zed as exchangeable gapage i s modified into less quasi-stream!ined permanent gapage. Shell shape may return to a non-quasi-streamlined form reminiscent of the shallow infaunal stage. Sculpture, lost in the 69
Figure 6. Rotation of the valves along a dynamic dorso- ventral axis. Anterior is to the right. The dorsal pivot is anchored at the hinge at point X. At the maximum anterior adductor contraction, the axis lies along line C-D, with a posterior gape. As the posterior adductor contracts, the axis sweeps an angle finally to lie at line A-B, creating an anterior gape. The posterior adductor moment, dependent upon the di stance to the axi s, is di f f erent as the axi s changes from C-D (distance 2), to A-B (distance 1). The anterior adductor moment behaves in the opposite manner. 70 Adductor moment
808 -
aaa -
0 S 10 15 as 35 40 45 50 55 Degrees
Figure 7. Anterior and posterior adductor moments for Tresus nuttali. Plot of raw data based on 2-3' measurements through ent i re ang1e of exchangeab1e gape rock i ng movement. (o ) - anterior adductor moment. (*) - posterior adductor moment.
Adductor moment
158 -
5 8 -
0 10 30 30 405 0 50 78 80 9 0 100 110 130 Degrees
Figure 8. Adductor moment lines for Tagelus divisus through entire angle of exchangeable gape rocking movement. Dotted lines indicate angles at which buttresses are positioned. AAM - anterior adductor moment. PAM - posterior adductor moment. 71
Adductor moment
I000
MS
MB
0 0 5 10 15 20 25 30 35 40 5545 Degrees
Fi gure 9. Adductor moment 1i nes for Resania lanceolata through entire angle of exchangeable gape rocking movement. Dotted lines Indicate angles at which buttresses are positioned. AAM - anterior adductor moment. PAM - posterior adductor moment.
Adductor moment 120M t ------1
>000
0 0 10 20 30 40 50 40 70 Degrees
Figure 10. Adductor moment lines for Siliqua patula through entire angle of exchangeable gape rocking movement. Dotted line indicates angles of buttresse positions. AAM - anterior adductor moment. PAM - posterior adductor moment. transition, remains absent as the substrate becomes the
primary protective device (Stanley, 1970). Shell thickness,
also originally protective, may be minimized (Stanley, 1970;
Morton, 1976). The teeth, reduced or weakly meshed in the
intermediate phase, may become rudimentary as all
shel1/shel1 movement is 1 ost (both along the hor i zontal
hinge line and along the dynamic hinge of exchangeable
gapage). The siphons may become partially or wholly non-
retractable, resulting in a decrease of the sinus depth.
Members of some species have been shown to possess an
atrophied foot as an adult, suggesting a sedentary habit.
Individuals of Panopea generosa, a hiatellid, may live
immobile in burrows 90 cm deep (Yonge, 1949).
Evolutionary Considerations
The majority of forms studied are uniform for the calculated parameters. The position of the umbo is distributed about a mode of 0.3 (Fig. 131). The depth of the sinus is generally less than 0.1 (reflecting the large numbers of members of the Unionoida in the study; Fig. 132).
Quasi-streaml ini ng is quite high, with a mode of 0.9 (Fig.
133), indicating that most bivalves, even shallow infaunal ones, are somewhat quas i-streamli ned. But high levels of exchangeable gapage and permanent gapage are rare (Figs.
134, 135). This indicates that most forms are still in the quasi-streamlining phase of the sequence. Few have made the 73
transition to the intermediate phase (Fig. 136). Why is this
the case?
To enter the intermediate phase requires a specific set
of shell characteristics. The umbo and cardinal teeth must
be central, the laterals must be able to disengage, and the
ligament must be short and centralized. Presumably, this
suite of morphological combinations is not met in the majority of bivalves. This has resulted in a bottleneck at the intermediate phase. Members of species occurring before this stage are abundant and diverse. It is hypothesized here that the acquisition of the necessary combination of characteristics needed to continue in the sequence may be determined by chance. Like billiard balls thrown at random on the table, one may drop in the pocket, but most continue rol1i ng.
Once in the intermediate phase, morphological change may be rapid. The change from intermediate phase to exchangeable gapage phase may be brief on a geological time scale. Radiation usually is rapid after a morphological or ecological innovation (Hoagland & Turner, 1981). Of the several hundred species of Mactridae, members of fewer than a dozen are in the intermediate phase, and the percentage is less for forms in the Cardiidae. Although members of the
Mactridae have been in existence since at least the late
Cretaceous, the groups now in the intermediate phase are no older than the Miocene. But within that small group 74 speciation may high. Beu (1966) has recognized three distinct lineages within the members of the genus Zenatia.
Geary (1987 ) found that slow rates of change in the
lineage of species of Pleurocardia are punctuated with quick major changes. Stanley (1977a) and Stanley & Yang (1987) al so found low 1 eve Is of phy1eti c change i n members of the
Veneridae and Tellinidae, two families whose members are still predominant1y in the quasi-streamlining phase. The bott1eneck ing of morphologies has created a steady, but 1 ow rate of evolution in these taxa. Even so, as stated by
Stanley (1979:118), "there is no evidence that a limit [to diversity] is being approached even after more than 400 Hy of radiation." But the acquisition of the intermediate phase must be seen as a major morphological step opening a new area ofthe morphospace. This type of evolution is consistent with the theory of punctuated equilibria (see
Stanley, 1979).
Within and after the intermediate phase, members of lineages would be expected to radiate to fill the new morphospace. As an example, the Anomalodesmata is a large, diverse group, with many of its members tending toward deep- dwelling, sedentary habits (Morton, 1977). The Solenacea is a large group of species, most in the permanent gapage phase. They are recognizable as solenaceans as far back as the Cretaceous, indicating that they had passed through the intermediate phase prior to that time. Most of the basic 75
adaptive radiation of the Bivalvia had occurred by the
Cretaceous (Nicol, 1986), even though 96* of the species,
and 52* of the families became extinct during the Permo-
Triassic extinction (Raup, 1979). This suggests that the
sequence of morphologies discussed here is an ongoing
process, taking place asynchronous!y in different lineages
as the necessary morphological prerequisites are obtained.
Is the evolution of these groups predictable? To a
certain extent the answer may be yes. If continued studies
show that other groups of bivalves lie upon these paths, we may assume that bivalve lineages entering a path may evolve toward the shell shapes of individuals already in the path.
The great degree of convergence in bivalves supports this hypothesis. Several groups, such as the mactrids and vener i ds , have members on both the my i d and sol enacean paths. Members of Resania look remarkably like those of its solenacean counterpart, Phaxus. They occupy the same pi ace
in the path. Will there eventually be a mactrid counterpart to So Jen? Members of Lutraria already have adopted the tube dwelling habit of that genus. SUMMARY
An hypothesis is advanced to explain: 1) the changes in
shell shape in individuals of species as a continuously
deeper infaunal habitat is colonized: and 2} the degree of
convergence in she 11 shapes among i nfaunal bi valves. A
maximum depth of burrowing for quasi-streamlined
morphologies will be reached as sediment weight becomes
significant. Up to this point, forms will adopt quasi
streamlined shapes for more efficient penetration of and movement in the substrate.
To achieve a deeper infaunal existence requires that the shell possess gapes through which the foot and siphons may extend. This would make the animal susceptible to predation and other immediate environmental dangers because
the shell functions as the main defensive mechanism. Only one morphological "solution" has been adopted by the
bivalves. This entails the antero-posterior rocking of the shell that produces alternate pedal and siphonal gape.
Because this action is brought about by the adductor muscles, rather than by the much weaker ligamental or haemocoel opening mechanisms, the problem of sediment weight has been bypassed at this depth. The
76 77
acquisition of exchangeable gapage requires several pre
existing morphological conditions. These conditions must be
modified for new functions in this stage of development,
termed here the intermediate phase.
The cardinal hinge teeth must still function as a
dorsal pivot, but on a dorso-ventral axis. These teeth must
be located centrally to maximize exchangeable gapage. The
laterals must be able to disengage (or no movement along that ax i s coul d take pi ace). The hinge must be centralized to avoid interference with the rocking motion of the shells.
This may be accomplished by a shortening the ligament or
internalizing it in a resilifer ventral to the umbo.
Movement into a deeper infaunal position may be possible once the intermediate phase is reached. This entails a further decline in predation and environmental extremes. At this point, exchangeable gapage may be modified into permanent gapage. The animal may be sedentary, with a reduced foot and externalized siphons. Shell thickness may decrease as the result of the reduced dependency on the shell for defense. Values of quasi-streamlining for these shells may decline as a consequence of a sedentary habit.
Comparisons between these models and the actual shell shapes of the individuals of the species studied show a general agreement. The morphologies are found in the predicted morphospace. The expected sui te of speci ali zed characteristics does occur in real species in the 78
intermediate phase. Members of lineages follow a specific
path, a sequence of body shapes, as they become increasingly
infaunal. This results in unrelated species shar i ng the same
general morphological pattern because they are at the same
point on this path. The constraints of sequence are such
that some paths may move in both directions, while in others
a separate course may exist for each direction.
Two paths occur out of the intermediate phase, termed
here the solenacean and the my id paths after the terminal
member of each route. The my id path contains the majority of
living species studied. The solenacean path differs as a
result of the behavior of its members, which construct tube
burrows. The shell retains its quasi-streamlining along with exchangeable gapage. The unionoids appear to lie on this path but the convergence is superficial. The members of that
group lack the fused mantle tissue necessary to form true siphons.
That so few forms exist in the intermediate phase or in the exchangeable gapage phase supports the idea that the specific suite of shell characteristics necessary to enter the intermediate phase has not been attained by most groups.
Shallow infaunal species, though high in diversity, are bottlenecked at this point. The entry into the intermediate phase may allow a new morphological radiation. This passage may be quick in geological time and be largely the product 79 of chance. This type of evolution best fits the punctuati onali st theory. 80
0.1'
I < I ’— i— i— i— i— r 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 IX permanent gapage
Figure 11. Plot of relative permanent gapage (P) and quasi streamlining (S) for all species. iue 2 Po o mrhsaeocpe b suidtx for taxa studied by occupied morphospace of Plot 12. Figure eaie emnn gpg () n qaisra!nn (S). (P) quasi-stream!ining and gapage permanent relative
quasi-streamli ni ng 0.1-j O 0.4 0.2 0.7 0.9 1.1 j O 0.0 0.1 0 3 0.3 0.4 0 3 0.6 0.7 0 3 0.9 0.9 3 0 0.7 0.6 3 0 0.4 0.3 3 0 0.1 0.0 ■f 82 0.6 o» 0.8- c c 0.7- £ o 0 0 .1- 0.6 0J 0.4 0,5 0.6 0.7 0 JB 0.9 1.0 permanent gapage Figure 13. Inferred channelization of morphospace for relative permanent gapage (P) and quasi-streamiining (S ). 83 1.1 ■ 101-i a.*. OJi 0.7 OX- ft. oo OX I OJ 05 OX- c 0 .1- 00) 1 I f " "T T T" I I 1 I «E OX 0.1 OX OX 0.4 OX OX 0.7 OX OX IX 1.1 © P ffl I to e T - r o 3 a .fo. *•. B OX- ox- OX I ox 0.1 ox -I— I — r - I I I I > I ox 0.1 ox ox 0.4 OX ox 0.7 00 O X IX 1.1 permanent gapage Figure 14. Plots of relative permanent gapage (P) and quasi- streamlining (S) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 64 l.i 1JO 03 03 -----*L. > ‘ 0.1 . 0 4 0 4 CA 0 3 o> c 0 3 0.14 E 0 3 r T 1 T-- r ■ I 1 1 I S 0 3 0.1 0 3 0 3 0 4 0 4 0 3 0.1 0 3 0 3 13 1.1 ® +J 00 I to « 3 o B 03 03 O.T 03 0 3 13 1.1 permanent gapage Figure 15. Plots of relative permanent gapage (P) and quasi streamlining (S) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. 85 l.l 1.0 OX 0 X h r 0 OX:p OX ox4 OJ u> OX c o.i4 ox 1 1 — I- ' T " " !'“ ■ "T I “ I T“ ' I E 0 JO 0.1 OJ OJ 0.4 OJ OX 0.1 ox ox IX 1.1 <0 ® +3 m i 1.1 (0 IX w » w $ <0 ♦ • ♦ 3 a 0.* ...... *• m ox * 0.7 * * B ox ...... ox ox * ox ox ► 0.1 ox 1 » 1 i "T * " T ' » 1 i 1 « 1 ' 1 > 1 » 1 1 * *" O X 0.1 ox ox ox ox ox ox ox O X IX 1.1 permanent gapage Figure 16. Plots of relative permanent gapage (P) and quasi streamlining (S) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 86 O) c - r 1-- 1 1 i I ~ i I < I ' I 1 i ■. i • i e O jO 0.1 0 3 O J 0.4 0 3 0 3 0.1 0 3 0.9 1 3 1.1 « © L. © 1.1 -P— tt 1 3 4 © Kik D 0.9 f 7 **** * ** * * "K a 0 3 ____ 0.7 B 0 3 * 0 3 0 3 * OJ 0 3 ’ 0.1 0 3 0 3 0.1 0 3 0.4 0 3 0 3 O.T 0 3 0 3 13 1.1 permanent gapage Figure 17. Plots of relative permanent gapage (P) and quasi- streamlining (S) for Tell inidae and Donacidae. a. Tellinldae and Donacidae species. b. Tell inidae and Donacidae morphospace (stippled) superimposed on plot for all species. 87 1.1- IjO. O-1-l* 0 J 0.1 0 J OJ 0<4 OJ' O) c OJ o.l-l £ OjO F~" 1 ' 1 I 1 T ' I 1 I 1 I * I - * " . " 1 T ' 1 I a OJO 0.1 O JOJ 0.4 O J OJ 0.1 O J 0.1 IJO 1.1 0 L- -P I a •" 1------m---- • ~ — *- a 3 .1 k ------CT -•— r- B I i — 1 ' T 0.1 O J O J permanent gapage Figure 18. Plots of relative permanent gapage (P) and quasi- streamlining (S) for Psammoblinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 88 1.1 IJO <► . * ■*;v o.o 0 4 0.1 04 0 4 04-| 0 4 o> c 0 4 0.1-1 E 0 4 i * I r — f— " I- ■ — i— I i I * I * I 1 •1 «0 0 4 0.1 0 4 0 4 0 4 0 4 0 4 0.1 04 04 14 1.1 9 L. +J (0 I (0 a 3 O' >r»ln* ■ ■ ■■ ....0 I 1^ 1 * * B 0 4 I T — I— ■ I T “ ■ —1 — — r~ " i * 0 4 0 4 0 4 0 4 0 4 0 4 0.1 0 4 0 4 14 1.1 permanent gapage Figure 19. Plots of relative permanent gapage (P) and quasi- streamlining (S) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for al1 species. 89 l.l ♦♦ 0.9 0.7- cO ’ 0 J . c 0.1- O jO £ O J 0.1 0 J O J 0.4 QJ O J 0.7 0 J 0.9 1J ® +J (0 I •r— to 0 3 a £-(. — I— B “ I— ~T ~ i i — r— OJ OJ O J OJ O J OJ 0.7 OJ 0.9 U l.l permanent gapage Figure 20. Plots of relative permanent gapage (P) and quasi- B t r e a m l ining (S) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 90 l.l IX- 0.9- OJ 0.1 ■ i ■■■♦- 0 j. OJ 0 A OJ CT> c OJ. 0.1 ox E ““I— ■ I ■■ ~r~ - T“ ■ r- ■ ~r '■ « ox 0.1 0 J OJ 0 A OJOJ 0.1 OJ 0.9 IX l.i 0 L. 4J 00 I » 0 3 O /V'-lWiT'■ rifll-iiTMM*.-- B 0.4 O J O J 0.1 OJ permanent gapage Figure 21. Plots of relative permanent gapage (P) and quasi- streamlining (S) for Myidae. a. Myidae species, b. Myidae morphospace (st1ppled) superimposed on plot for a 11 species. 91 l.l o.i C 0.1 OX 0.1 B i < i ■ i ■ i ■ i OX 0.1 OX OX IX permanent gapage Figure 22. Plots of relative permanent gapage (P) and quasi* streamlining (S) for Unionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species, c. Hypothesized interpretation of plot as a channelized morphospace. 92 ft ' 9 CT> 9 a * * 9 0> O » * n 9 0.2S< 9 a» c OJO 0.3 P9rmanent gapage Figure 23. Plot of relative permanent gapage (P) and relative exchangeable gapage (E) for all species. iue 4 Po o mrhsaeocpe b suid aa for taxa studied by occupied morphospace of Plot 24. Figure eaie emnn gpg () n xhnebe aae (E). gapage exchangeable and (P) gapage permanent relative exchangeable gapage 0J5- Q.4G- 0.45- 0.S0- 0.55- . m s m mm ^ e* [ij aj emnn gapage permanent MaMpMwrnf •V*/V*. t ■*» Wffip y v ^yijfwy* y yy>v\^ 93 94 0.55- 0.50- O o> 0 a « a> n 0 0 o> c 0 o X 0 permanent gapage Figure 25. Inferred channelization of morphospace for relative permanent gapage (P) and exchangeable gapage (E). 95 Oil OJO OAf OAO OJS OJO OJS OJO o.u o 0.10 O) . _ 0 0J» a a o j o I I — 7— I — ■r~ “ T" “T“ — T— °> OIJ J 0.1 OJ OJ 0.4 OJ OJ o.i OJ OJ 1J 1.1 B 0.1S- t - T* ■ I —I— i— t ' OJ OJ OA O J O J 0.1 OJ OJ IJ 1.1 permanent gapage Figure 26. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Cardi idae. a. Cardiidae epeciee. b. Cardiidae morphospace (stippled) superimposed on plot for all species. • 96 OA ojo OJS4 0 .40 OJS OJO OJS o j o 0.1E 9 0.10 O) 0 0-00 -r a * 0 JO *— I ' I ' I 1“ -I— — r~ oi OJ 0.1 OJ OJ 0.4 O J O J 0.7 OJ 0.4 1 J 1.1 n 0 ® o> c OA • 4 1 0 * £ OA O X OJS 9 • ♦ OJO 4 4 OJS B 4 OA - f. ■ ——..1 • • 4 OJS • 4 4 OA 4 0.1S J « 4 • 0.10 4 i 4 A. OJS w * * p . —-fc- . . OA ■ 1 * T J 0.1 O J 0-3 (M OS 0-& 0.7 O J 0.4 IJ 1. permanent gapage Figure 27. Plote of relative permanent gapage (P) and relative exchangeable gapage (E) for Veneridae. a. Veneridae species. b. Veneridae morphospace (stippled) superimposed on plot for all species. 97 OJS OJO' 0<4E‘ 0,40' OJS OJO OJS OJO o.is- © 0.10 C7> e OJE a a ' ' T ■ i r i O) DJ 0.1 OJ 0 J 0.4 OJ OJ 0.1 O J OJ 1J 1. A a © o> c a " ■ • B A U X ...... ^ . 0 :...... © 0 m * * jfH ♦ B " " J P F "" • OJO ♦ ♦ OJS + M * ♦ OJO 0.1S • ■ 2 * » j- '■y&M 0.10 *■_ V ...... ••••„. lV* * OJOS • * OJO t ■ 0.1 0 J O J 0.4 O J O J 0.1 O J O J IJO 1.1 permanent gapage Figure 28. Plots of relative permanent gapage (P) and relati ve exchangeable gapage (E) for Mactridae. a. Mactridae species. b. Mactridae morphospace (stippled) superimposed on plot for all species. 98 0 J5 oio OJE OJO OJS OJO OJS ojd V O.IS 0.10 I oj* ¥ & - fj o JO IT— , , I 111 I —T“ — 1— O) O J 0.1 O J OJ OJ 0 J OJ 0.1 OJ 0.9 I J 1.1 ® OJS OJO- B OJO ■ t i I i I T“ I t » OJ 0 J OJ OJ 0.1 OJ 0.9 I J 1.1 permanent gapage Figure 29. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Tel Unidae and Donacidae. a. Tellinidae and Donacidae species. b. Tellinidae and Donacidae morphospace (stippled) superimposed on plot for all species. 99 OA OJO OXS 0X0 OJO OJO OJS OiOr 0.1S « 0.10 o> 0 a 0J* t e 0 0X0 I - ■ I ' I ' ' I I I ' I < I 1 1 1 I o> OX 0.1 0 J 0 J OX OJ OJ 0.1 « J 0.9 IX 1.1 XI 0 0 CT> OA c 0 -C 0X0 o X ox« 0 0X0 0X6 B OJO OJE OJO 0.16 ;|P v 0.10. ----- p : 0X0 ^ “1 I, I i I 1 T" ' * I * " I * I 1' I 1 t 1 O X 0.1 OJ OJ OX OJ OJ 0.1 O X 0.9 IX 1.1 permanent gapage Figure 30. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 100 OJO 0.40 - 0.10- CL B OJO- O) OJ) 0.1 0 J OJ 0.4 OJ OJ 0.1 OJ OJ 1J> 1.1 n m ® X'' . u> OJS c « 7 7 ?’ ~ £ OJO o X OJE ... 'J- “- "*t" ! 1 ‘'''I1.'"! I'1'" I1.11 1 'ijrJ - . ® OJO B OJE jiftM\? ij.ll 11 l.l *1111\ vTi^l OJO > » ; ; a ____ OJS 0 JO-- -y* '■ y^y* j - y :.. t* 0.16 *»***,»»*» k J-* 0.10 IT mflii iiVwim OJE ■ pif------OJO —T- t1 OJ) J 0.1 OJ OJ OJ OJ OJ o.i 0.1 OJ 0 . 1 u 1.1 permanent gapage Figure 31. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Solenacea. a. Solenacea species. b. Solenacea morphospace (stippled) superimposed on plot for al1 species. 101 o j s o j o OJS- 0 AO OJS OJO OJS- 0 JO O.IS. e 0.10 o> 0 OJS a 0 OJO ’-I — 1 " — T " r~ u> O J 0.1 OJ OJ 0 A OJ 0 J 0.7 OJ OJ 1J 1.1 .O 0 0 o> c • 0 • £. o X « * * * * 0 B 0 ...... ♦ * 0 • OJO - O.IS 0.10 OJS h r ^ _ OJO ST...... I ' I —1—* 1 « f ■----- 11 1 * 1 f — — 0.1 O J OJ OJ O J OJ OJ OJ ■■ 1Jt 1.1 permanent gapage Figure 32. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 102 OJS o j o OAt 0A0- 0J5- OJO OJS OJO O.IS O 0.104 O * OJS a m OJO I “I — r— O) OJ 0.1 QJ OJ 0.4 OJ OJ 0.1 OJ OJ 1J 1.1 J) ffl 01 o> c ojs 4 fl £ OJO o X OJE- ® 0 JO- B OJS OJO OJS o j o ■ O.IS- m;. ““I - —r“* — t- — 7— OJ OJ QJ OJ OJ 0.1 OJ permanent gapage Figure 33. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. 103 -Q OJOO 0J> 0.1 0.2 O J 0.4 OJ O J 0.1 O J 0.9 iJS 1.1 permanent gapage Figure 34. Plots of relative permanent gapage (P) and relative exchangeable gapage (E) for Unionoida. a. Unlonoida species. b. Unionoida morphospace (stippled) superimposed on plot for all species. 104 O O.tO- o E 3 C O (0 ao 9 > oxoJV-&-ft-B 4-> L * « 0X5' 0X0 OX OX permanent gapaga Figure 35. Plot of relative permanent gapage (P ) and relative position of umbo (LI) for all species. iue3. lt f opopc cuid y tde tx for taxa studied by occupied morphoepace of Plot 30. Figure eaie emnn gpg () n rltv psto o umbo of position relative and (P) gapage permanent relative (U). relative position of umbo □ — aOO 0 ■ *£E - o/rs.£; O.SO-I 0.0 ------irtliww^y.i'V" r*r i u!rl ...... •■ i ! i '/ i V yV'iY . * - - ’ - > ^ - L , ‘ * J l ^ , i V l n > V f ' ~ i ‘ i > r ' ' i l r f * i * i * i n ' l V f ^ ' i i a r r A i ' i ' i 1 i V i V ' i j i i i X l ^ * ^ V i T ^ r i i f c 4 « V « i i M X i ! ^ * * ' l l i * i V i - f i Y r l|{ji — ^>H ■ > ifMI * *<*>> *« W t 5 ...... * k s & S ( ...... yr«.^ .^V.*W*W >.H*^ W iw *rt*»y ; . J . 0.5 0.4 OJ emnn gapage permanent : iUi||!|!|J^^^Ui[b^2Llltltl£ii&Uht!iAllLf>!^U^bfli> S e i frH < Hi' ■ W ffrWj>‘ir "Sfe i >'i*t 5 : : : : : : :■ v x* ;5x -x :•:> ! ■:•:*: - ...... — jwBWWfew»- * ■ * •"rtjy.'H . fc* - > »«■>»*»*- ...... *■• 105 iue 7 Ifre canlzto o mrheae for morphoepace of channelization umbo of poeition relative and (P) Inferred gapage permanent relative 37. Figure CU). relative position of umbo . 01 . 03 . 05 . 07 . 09 1J0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.S 0.10.0 emnn gapage permanent 106 1.1 1 0 7 040 o.n-i o.to 040 0 ■*— i— ' i ' i i t » “ r 1 i— i y 1,11 I I 04 0.1 04 OJ 04 04 04 0.7 0 4 0 4 14 1.1 permanent gapage Figure 38. Plots of relative permanent gapage (P) and relative position of umbo (U) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 1 0 8 tJO O.IS 0 .10-1 Oit 0 JO-1 OJS 0J0+ OJS OJO- OJS- o j o OJS# OJO- O.IS o.to OJS C O OJO - r I I 1 ■ I - r ! ■ — T“ T" I OJ 0.1 OJ OJ OJ OJ OJ 0.1 OJ OJ 1J 1.1 <0 o a OJO e > O.TO- •p 0 B 0.10- ■*T I ■ I " I ...... —T” O J 0.1 OJ OJ OJ OJ OJ 0.1 OJ OJ 1J 1.1 permanent gapage Figure 39. Plots of relative permanent gapage (P) and relative position of umbo (U) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for al1 species. 109 OJO O.IS O.TO- OJS OJO OJS OJO OJS OJO OJE-t f OJO OJE OJD O.IS 4 0.10 C OJE 4 o OJO I I” - r- -I— — r— 1 "T 1~ T " I 0 J 0.1 OJ OJ OJ OJ OJ O.T OJ OJ 1J 1.1 <0 o a OJO ® > O.TO- +J « ® L. B % * * OJS — OJO- w OJO o.is 4 •• 0.10 OJE ** OJO ■ I I ■ T 1 T— "■ T '■ OJ 0.1 OJ OJ OJ OJ OJ O.T OJ 0.9 1J 1.1 permanent gapage Figure 40. Plots of relative permanent gapage (P) and relative position of umbo (U) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 1 10 0<40 0.76 0.70+ OJS OJO OJS ~r o j o 4 "W OJE 0.40 OJS OJO o n OJS £ OJO 3 O.IS o.to c OJE o OJO — I— 1—T—r—r— — P “ I" ■ r ■ I — r- — t— OJ 0.1 OJ 0 J 0 A OJ OJ 0.1 0 J OJ 1J 1.1 QO o a ® > ■p « e 0 J o fcS&!. L. B * * + • -+ p r . • ------*— ...... 11 • T . t ...... v ---- ** • JO OJ 0.1 OJ OJ 0.4 OJ OJ 0.1 OJ OJ 1J 1.1 permanent gapage Figure 41. Plots of relative permanent gapage (P) and relative position of umbo (U) for Tell inidae and Donacidae. a. Tell inidae and Donacidae species, b. Tellinidae and Donacidae morphospace (stippled) superimposed on plot for all species. 1 1 1 OJO 0.1® 0.70 OJO OJO OJE o jo 4* OJE • » OJO OJE OJO o o OJE e OJO 3 O.IS 0.10 OJE 4 C O OJO — r— T 11 — I— — r~ I ■ 1 '■ ■ I I OJ 0.1 OJ 0 J 0 J o!s OJ 0.1 OJ 0.9 1 J 1.1 co o a 9 > •r~ 4-> «s i. B \*i * • f 1 * » • — v ... ¥ * ♦ i * .... - ... * * - i OJO OJ 0.1 O J O J O J i.i permanent gapage Figure 42. Plots of relative permanent gapage (P) and relative position of umbo (U) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 1 1 2 040 0.16 0.10 040 040 040 046 040 046 040 O n 046 E 3 040 0.16 0-10- * 046 V4 X 040 — r~ — i1 T" — r— I " i — r~ “ T— 1 ’ I 04 o.i 04 04 0.4 04 04 0. 1 4 4 04 14 1.1 (D O a 040 9 > rr~ 0 .10'1 -P c 046 040 L. 046 040 046 B 040 040 040 9 0.10-> E5 E£SEZ2 3 S^SSSZ 046-i 040 -i— • 1 * 1 T 1 > 1 ' 1 ' 1 ' 04 0.1 04 04 04 04 04 0.1 04 04 14 1.1 permanent gapage Figure 43. Plots of relative permanent gapage (P) and relative position of umbo (U) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. 1 13 OJO 0.7* O.TO OJS OJO a Si o j o - OJE' OJO 0 JS- OJO- £ OJE E OJO 3 0.1*4 0.10 0 J6-| C O OJO — r— — r~ I I I ' I “ 1“ ' 1“ I t OJ 0.1 OJ OJ OJ OJ OJ 0.7 "OJ OJ 1J 1.1 to o a. 9 > 9 mr&ft ® L. aUlii .1 |I WI .i»i>»ii.iiiiii i! ii.;'.,!.1 r..T. i^iji tf iM j W r . _ ...... B T1*®-"... • ■“'■■' ■ M i . • I— .«------t * • * • A...... , ...... ^ • OJO 0 J 0.1 0 J O J 0.4 OJ OJ 0.7 OJ O J 1J i .i permanent gapage Figure 44. Plots of relative permanent gapage (P) and relative position of umbo (U) for Solecurtinae. a, Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 1 1 4 OJO 0.75 0.70 OJS OJO OJO 0 JC OJO OJO O o OJS E OJO 3 0.15- 0.10- C OJOS O OJO T" T” -I— '! T I — r~ — r- I — r - OJ 0.1 OJ OJ OJ OJ 0 J 0.1 OJ OJ 1J l.l a> o a OJO a > -r- 4* c B 0.10- 111 — |------1— I— f— I— l——I— I 1 I - ' | - ' T - o j o.l O J O J OJ OJ OJ 0.1 OJ OJ 1J i.i permanent gapage Figure 45. Plote of relative permanent gapage (P) and relative position of umbo (U) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for al1 species. 1 1 5 040 0.15 0.104 045 040 0 4 5 0 4 0 4 046 040- 045 040 O -O OJS E OJO 3 0.15 0.10 C OJS -v o OJO — I— I I I I ' I ■l I OJ 0.1 OJ 04 0 4 0 4 04 0.1 0 4 04 1J 1.1 (0 o a 0 > ■P a 0 u B . j . OJS- u p 04 04 04 04 permanent gapage Figure 46. Plots of relative permanent gapage (P) and relative position of umbo ((J) for Unionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. 116 to 3 C ■r~ <0 £. a 0 TJ 0 > *r” +j « 0 U OJ) 0.1 0.2 0.3 0.4 Q.S 0.6 0.7 permanent gapage Figure 47. Plot of relative permanent gapage (P) and relative depth of sinus (N) for all species. 1 1 7 0.9 0 «8 * mvmYhylyMMVhvWw7www.11 ^* 0 jaMRp^'. * *^“,1 m/, >'/, ■ MwAVA:! V\WvAV*V,.V>,,i'v* ’* * permanent gapage Figure 48. Plot of morphospace occupied by studied taxa for relative permanent gapage (P) and relative position of sinus (N). 1 18 » 3 C <0 £ 4-> a « T3 0 0-3' a OX- 0 u OX 0.1 OX OX 0.4 OX OX 0.7 OX OX IX 1.1 permanent gapage Figure 49. Inferred channelization of morphoepace for relative permanent gapage (P) and relative position of sinus C N ) . 1 1 9 OJ -- (0 C a ® ^ o j a OJ 4-> 0 ® L. O.J *__ u 1.1 permanent gapage Figure 50. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. T3 01 *i *n -*■0 • -• O 0 —* 0.1 0.1 0.4 o ox T> 0.* O > L *--- o.i- cr . 0.4 O.i OX O.i OX O X 0.4 permanent gapage Figure 52. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 122 0.9 OJ O.T- \ 0 J * ♦ « OJ 0.4-; OJ' (0 3 C OJ •r~ <0 0.1 + OJ — 1— 1 1 ■ I ' ! - '■ 1 ■ 1 I I - “I £. 0.1 O J OJ 0 A OJ OJ 0.1 OJ 0.9 U 1.1 +>a 0 J 9 TJ 9 > -*-> . « A; :> , vv-,.. 9 L. or- B I.V.V.AV. . W-V f t ” . •• • i ~i - - r - I O J 0.1 O J O J o!T OJ OJ O J 0.1 0 J 0.9 1J l.l permanent gapage Figure 53. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Tellinidae and Donacidae. a. Tell inidae and Donacidae species. b. Tellinidae and Donacidae morphospace (stippled) superimposed on plot for all species. 123 0.9 OJ (0 3 C OJ m *•- 0.1- o ® T> > e r— 0 L. ■S£W. B £ *» * .! » © ♦ • * *------ j f ■"**) " ■—*1 1 ' 1 - oj) 0.1 OJ OJ Cj OJ OJ ' OJ 0 j 0 j 1 j 1.1 permanent gapage Figure 54. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 124 o.* 04 0.1 04 OJt-i 04 04 CO 3 c 0 4 •r ♦ * ♦ CO 0.1 -C 04 T" -r- +J 04) 0.1 04 04 04 04 04 0.1 04 04 14 1.1 a a n « > ■p a ® B h m m m permanent gapage Figure 55. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. 125 o.« 04 0.11 OJ CO 3 c 04- at o.i 04 i.i e o.« > 4J 04 0 0.1 ... ______■ ♦ 04 04 B 04 '*** . .-*«■ OJ 04 ** ♦ 0.1 ►V~~ OJJ i 1 — I— — r— “" ( ' — r 04 0.1 04 OJ 0.4 Q4 0 4 0 . 1 0 4 0 4 14 i.i permanent gapage Figure 56. Plots of relative permanent gapage (P) and relative depth of sinus (N) for solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 126 0.7 OJ O •O 0*71 > 4 • £7 .. . " e ♦ « 0*7- '■'•*4 ' •"...... ' .. L. ' * 0 J- OJ 0.4.0 4. » * * 0J- * * * ♦ * * J 4 i A J .» hf 4 4» * 4 4 D.lJE4 .0 * ... 4 ... ojo\ 0 JD O.J O J O J OJ OJ O J 0.7 0 J 0.4 1.0 1.1 permanent gapage Figure 57. Plots of relative permanent gapage (P) and relative depth of sinus (N) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. 127 o . t 0-7 0 -S 0-4 <4- o ® X) 9 L. 0.1 Oil OJ) 0.1 OJ OJ 0 -4 OJ OJ 0.7 OJ OJ 1J> 1.1 permanent gapage Figure 58. Plots of ralativs parmanant gapaga (P) and ralativa depth of sinus (N) for Unionolda. a. Unionoida speclas. b. Unionoida morphospace (stippled) superimposed on plot for all species. 1 2 0 1.0' d'O' * * 4 * * * 7 0.9- ■cA— *- _ _ o j O) C 0.7 * * 0 >6' 6 -•«- e 0 0 aS ‘ "I 0 L. -P 0 0 A I V 0 0X4 0 a OX- 0.1- • OX 1----- 1----- > I 1 1 1 III ----- 1---- OJOO 0 X6 0.10 0.15 0 X0 0 X5 0 X0 0 X5 0.40 0.45 0 X 0 OXS exchangeable gapage Figure 59. Plot of relative exchangeable gapage (E) and quasi-stream1Ining (S) for all species. 1 29 * hy11 ^3 H11 BMlMllfWWjCT ?* » .ft t* ■ ftT-T o> c ■h>h;.i E 8 vw.v.v.lfW' 9 :-x?:<::-:- L. +J (0 ) ■T- (0 8 3 a exchangeable gapage Figure 60. Plot of morphospace occupied by studied taxa for relative exchangeable gapage (E) and quasi-streamlining (S). 1 30 1.1 1.0< o> 0.0- c c 0.7- E « ^L. 0.5- to i - 0.4- to 5 0.3' o 0.1* 0.1 0.4 exchangeable gapage Figure 61. Inferred channelization of morphospace for relative exchangeable gapage (E) and quasi-streamlining (S). 131 l.l 1J0 o.i o jb 0.7 OjS ♦ • * OJ 0 A OJ c 0-* c o.l 0.0-- B 0.00 o j s o.'io o.'is o jo 'o J e s o jo o j c oJ«o oJ»* o.ko s j exchangeable gapage Figure 62. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 1 32 i.i 1 J o.»4 OJ 0.1 d j 4 OJ 0 j* 0J4 05 c OJ 0.1 E OJ " i i r i r 'i'~ i i i 1~ 0JO 0JC 0.10 0.1S OJO 0J6 0JO 0 J5 OJO 0.46 OJO OJE 9 L. 4-5 0) I 1.1 0) « ♦ * • j * * # t • * ...... *4 3 * * ** » » • a o.« • t — * -* ~ M------* ------* ------— OJ 0.1 OJ B 0 J 1 r ? r OJ OJ OJ 0.1 OJ* 1 iiii r"i i i i ■ i i i_ OJO 0J6 0.10 O.U 0JO OJS QJO OJE OJO OJE OJO OJE exchangeable gapage Figure 63. Plots of relative exchangeable gapage (E) and quasi~stream11ning (S) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. exchangeable gapage Figure 64. Plots of relative exchangeable gapage (E) and quasi-atreaml1ning (S) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 1 34 i.i 14)-) 0.1 >«*>■ A*** . OJ • * 0.1 I f o j 4X------OJ 0 J OJ CD 0J4 c o.i OJ 1 '" T "I I" " I I ■■■■ ' E O jOO OJS 0.10 0.1S OJO 0J5 OJO 0. ojo ojs o^o ois e ® L. 4-> CO 1.1 I (0 i>04 (0 •• 3 0.1 * 4 * a OJ 0.1 K t L u l J . . .. Sir♦ * OJ B * ? r OJ OJ OJ OJ o.l' OJ. — i----i i-----r— :— i i — t" ■ "1 I I I OJO OJS 0.10 0.1S OJO 0J5 OJO OJI OJO OJS OJO OJS exchangeable gapage Figure 65. Plote of relative exchangeable gapage (E) and quasi-streamlining (S) for Tellinidae and Donacidae. a. Tell inidae and Donacidae species. b. Tellinidae and Donacidae morphospace (stippled) superimposed on plot for al1 species. 135 1.1 1 JO 0.9 OJ 0.7 OJ 0 J OJ OJ o> OJ c C 0.1 I- 0 J E OJO OJS 0.10 O.iS OJO OJS OJO 0J5 0.40 0.45 OJO OJS (0 ® ■p '.'.■li'VK'J.iW1'1'1''"' exchangeable gapage Figure 66. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 136 1.1 IX T'*~ # ♦ ♦ 0.* * ox 0.7. OX ox ox ox CD ox c 0.1 ox ■~i '■ ■ i i i i i i ■ ■ ■--- r ~ E 0X0 0X5 0.10 O.U 0X0 0X5 0X0 0X5 0X0 0X5 0X0 0X5 0 0 +J 0 1.1 1 0 IX 0 ♦ r--^*: * i). ;ir ^ 3 ■ ** * ♦ X I .■«.... — ...yfi ■•..- ...... m---- C7 0 J lii *^~r * *.-„ ^ - 7 - 1 B I I I I . I I ' I T '■" i — i {_ 0X0 0X5 0.10 0.15 0X0 0X5 0X0 OX 0X0 0X5 0X0 0X5 exchangeable gapage Figure 67. Plots of relative exchangeable gapage (E) and quasi-streamlining (S) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. 137 1.1 1.0 OJ. * * *♦ OJ o.l. Oi' OJ 0J- OJ CT> C OJ 0.1 E OJ I I I I I I ""I I . . « OJO OJS 0.10 0.1S OJO OJS OJO OJS OJO OJS OJO OJ a L. +J CD 1 1.1 <0 « 1J 3 ♦ ♦♦ • Or OJ. *£ * OJ 0.1 e ~ OJ B ♦ ♦ OJ OJ 0 J OJ 0.14 OJ I I I I I I I 11 I '1 I I OJO OJS 0.10 0.1S OJO OJS OJO OJ OJO OJS OJO OJS exchangeable gapage Figure 66. Plots of relative exchangeable gap&ge (E) and quasi-streamlining (8) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 1 3 8 i.i 1 JO- 0.9. OJ O J- 0.1- - U J I " T I ■1 i l ~ .— I I " I ~ *T~ I I ™- l_ l,-‘ Qja a OJS 0.10 O.IS 0X0 0X9 0X0 OJE 0.40 0.4E OJO OJE exchangeable gapage Figure 69. Plots of relative exchangeable gapage (E) and quasi-stream1ining (S) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. exchangeable gapage Figure 70. Plots of relative exchangeable gapage (E) and quasi-stream!ining (S) for Unionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. 140 0.9 6° *0 *©*0® « 0.7- -xy*'... j-.... -...... — - . 3 ♦ 4 ♦ -r~C to OX* A-H- 1-... -— ...... -—- a, A6 ^ 0 * £ + 46 * 6 v 4w * O _£ 4 ••*--. ■ ■ -* T ---T TTT Iinr- ~ AJL ▲ -C P 4 ° * * > a • jk 4 ..... 4______© TJ °*4 V 64 4 " ----- ♦ 4 4 tt 0 ^ 4 « S » 4 ...... -4... > 4 4 4 4 4 4 P fi ii•<^ ^ 4 14, 4 0.1- 5*4 »___ 4____ 4....4__ ...... ■ ...... ■ . ^ UM r i i 1---- 1----- 1---- 1---- 1---- 1----- 1---- 1----- 1--- 0X0 0 X5 0.10 0.15 0 X0 0 X5 0.30 0 X5 0.40 C.«S 0X0 0X5 0X0 exchangeable gapage Figure 71. Plot of relative exchangeable gapage (E) and relative depth of sinus (N) for all species. eaie xhnebe aae E ad eaiedpho sinus of depth for relative (E) taxa and studied gapage by exchangeable occupied relative morphospace of Plot 72. Figure (N). relative depth of sinus ' . V . W . V - V i V A V xhnebe gapage exchangeable •Wv V A ' * W . ’ . W 141 PLEASE NOTE: Page(s) not included with original material and unavailable from author or university. Filmed as received. UMI 143 0.4 0.1- « 3 C 4- O 0.1 0.4 a ® •a 9 0.9 > 0 J A A * ♦. * ...... * ^ 0.1 A 4**: i. i * r . * OJ A* OJ ^ ^ " -- B A A OJ ; ..: • A A* • A OJ A 4 * 0 J 4 4 0.1 * 4 OJ i i y OJO OJS 0.10 0.1S OJO OJS OJO OJS OJO OJS OJO 0. OJO exchangeable gapage F1gure 74. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 144 04 0.1 04 0.4 W 0.1- <*- o OJO 0.1 a a> ® 04 > +j> 04 * — * L ♦ * .. - m A. ***** 0.T r 44'"*- • — ...... — ... 04 ♦ * 04 B • 4 S S H O F ' ♦ » 04 * * • 0 4 I .turn ^ ■* ♦ ♦ #:)k . • ■ ♦ * 04 ‘ ‘ . ‘ * 0 .1 jjtijfc * * * * * 0 4 [ 1 ■’ 1 1 -T ---I---" I ™ T -- “ I----1-- T. -- V—- exchangeable gapage Figure 75. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. 145 0 J S :* C OJ..— *• « 0 . 1 ----- o ox 0.1 a « TJ ® 0.4 > ‘r— OX * * • ...... a * \ « O.T AwpiTwaiiv.t - t * * : • .....- ...... 0 4 ♦ * 04 W-ji - B • 04 ^ , r r ^ . * * . OX >.,■ ♦ *4 -4 ^ 0 J 4...... ■ • 0.1 f * * » -I**:.;, ox T1 1 T 1 — exchangeable gapage Figure 76. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 1 46 CD* °*3' 3 C OJ- CO 0.1- o 0.1 0.4 a 9 ■o 9 0.9 > ■S:" V -P 0 J 4 m. 1'tbjt ijcr$h 0 ‘X y l v i w . v ! 1.' 9 0.1 L. V ' ^ - ^ 4 - ' - / OJ vfoi; i.vi I..-..».v------♦ * OJ ______B OJ j *** -- OJ * * **. • OJ 4U»~ 0.1 OJ 0jo 0js 0.10 O.'l* OJO OJS OJO 0js OAO OJS OJO OJS OJO exchangeable gapage Figure 77. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Tellinidae and Donacidae. a. Tellinidae and Donacidae species. b. Tellinidae and Donacidae morphospace (stippled) superimposed on plot for all species. 1 47 0.9 — 4 0.4- OJ- (0 3 C OJ CD O.J 4- O OJ) ■C 4J o.i 0.4 a a> a> OJ > +J o j -l*— *♦-«-*- a % ***♦** A 0 . 1 $ 5 T f?:: -■■■' 04 ¥>l* >jW n ■ y i . l WI.D>««« IWIMI IIIH ll'iMiI OJ B — •— — ♦ .* -4>- * * 0.4 m 5 5 ? " “ i. ft--- O J * ♦ •• 4 4 • ... OJ ft ft * «» * • 0.1 ♦ 5 f . -•— * * ------•---- 0 J OJO OJS 0.10 0.1S OJO OJS OJO OJS 0.40 Gd4S OJO OJS OJO exchangeable gapage Figure 78. Plots of relative exchangeable gapage (E) and relative depth of einus (N) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 1 4 8 OX OX 0.7 ox4 OX 0 A- © OS 3 C OS 0.1 -C ox T" ■"I — i — r— P o x 0.1 OS a x 0.4 os a o T) © > • r * P © © 0.7- ♦ ---•* L. i* • • B w1 iMiittfWii©***! 0X0 OXS 0.10 0.15 0X0 0X5 0X0 0X5 0.40 0.45 0X0 OJS 0X0 exchangeable gapage Figure 79. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. 149 0.41 04 0.1- 0 4 1 04- 04- to OX- - 3 C 04 0.1. x: OX- —T“ — I— 1 ■T +> OX 0.1 04 OX 04 04 a © T3 © > 4-> a a L. B ' - w m m m ♦ ♦ ♦ 04 . * _ _ ♦ ______ 0.1 OxJ- t 1 t i " r i i t i i —r OXO OXE O.X 0.1* 040 046 0X0 OX* 0.40 041 040 OX 040 exchangeable gapage Figure 60. Plots of relative exchangeable gapage (E) and relative depth of sinue (N) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 1 50 o.« O.T- 0.1 0 . 4 OJS 0.9 > -P OJ ft * 6 % w % O.T .... — .. — ---- i * # . * 0.* •» ' ♦ i " % ** * * B • * * * * ; *— * V' £ » * --- \ *. • * « « * ... . * « * . . . * ...... * . « 0-0+. 0.00 0.06 0.10 0.1S 0.20 0J1 0JO 0J6 0.40 O j4B 0. OiS OJO exchangeable gapage Figure 61. Plots of relative exchangeable gapage (E) and relative depth of sinus (N) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. 151 H- 0.1 O 0*4 0J 04 B ♦ • ♦ 0.4 ~e; o j - * « * • 0 4- 0.1 ..♦-.A . 04 f*1 I I I I I ~ T— " I I I ' I 040 04S 0.10 O.lS 040 045 040 0 45 0.40 0.45 0 40 0 45 0 40 exchangeable gapage Figure 62. Plots of relative exchangeable gapage (E) and relative depth of alnus (N) for Unlonoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. oiin f mo U fr l species. all for (U) umbo of position iue 3 Po o qaisra!nn () n relative and (S) quasi-stream!ining of Plot 63. Figure relative position of umbo 0.20. 0.30- 0.35- - 0 ^ 0 0«46' - 0 ^ 0 0.55- 0.76- 0.80- 0JJ0- 0.05- 0.10. 0.15- 0.2S. 0-60- 0-65- 0.70- 0.0 0.1 J— — 0.2 r~ — quasi-stream!ining J O ““I— 0.4 I— “ 0.5 T— — 0.6 I • I‘ 0.7 .•* *6 * • A. r 1 “ 0 0 Jt I I— — o.e T— — IJO 152 1.1 us-temiig S ad eaiepsto fub (U).umbo of position relative (S) and quasi-stream!ining iue6. lt f opopc cuid y tde aa for taxa studied by occupied morphospace of Plot 64. Figure relative position of umbo 0-00. 0.90 x o " T 0.1 0.2 quasi-stream quasi-stream 1ining 0.3 (,4, t*‘t * *’, 0.4 0.4 ([,. t 0.5 • i ' , * * ' * V , ' * ’ • ;;;V< ’ , * / * ■ ■ ? ; ♦ *A* * / t f f l f i Sffj . ; j » : • + . : », * ■ ■ : i 0.6 - • . * - ■ • ■ 0.7 • : ' ■ :•.:• *• i ,* ■* i*,*1 * * 0 i" 3 *.1 ' *. f;**??#,**»i',‘ 0.6 if**!** T" X;t>' ' .1' J;«:.il i . : « ; .J t. 1,'; U I* ’'fI*'4ft »t t » r . M B j t > t 4 ' I.*' .’,'f * f I ■ .‘,v«i; **i.* ’VaHwC- '* fury I " T 0.9 ,’ ■ ; 4 - P - IX 153 1.1 temiig S ad eaie oiino ub (U). umbo of position relative and (S) streamlining Figure 85. Inferred channelization of morphospace for quasi for - morphospace of channelization Inferred 85. Figure relative position of umbo 0.00 0435 0.10 0.25 0.15 0.30 0.35 0.20 0.40 0.45 0.SE 0.60 0.50 0.60 0.65 0.70 0.75 041 0.1 0.2 quasi-etreamlining 043 0.4 0.5 0.6 0.7 0.6 0.6 14) 1 54 1.1 1 55 040 O.TK O.TO- 04C 040 04C - * 4 - - 040 04E *• 0.40 046 * : z 040 O -4«4. A 046- E 040 3 0.16^ 0.10 046-1 C O 040 -I— I ■—T" '“T 11 --r— r- “ T" "T“ "T" —T” 04 0.1 04 04 0.4 04 04 0.7 04 04 14 1.1 00 o a. 040 « > a o B •i/v>j u>m ^** * hm mylffbytiJklMW&iiMl fii.l.lj\\mm' ■ ■v y .* .^ r .y>:sv-^.'-xyV&yy.' > ■: : ► - w , n H ii'r'riri^irthi^Vr'fi .; &>XiV M m MMM i;i ij iiiii i ii n j,i ji#i. rjjt *V. ’■ ' . **' ;-i — ^£7-' ‘1 r ■ HW mii 04E quasi-stream1ining Figure 86. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Cardiidae. a. Cardiidae species. b. Cardiidae morphospace (stippled) superimposed on plot for all species. 1 56 0X0 O.T* o .t o O i S 0 x 04 0 AC 0X0 IMS 0 X 0 OX* 0X0 & 0XS E 0X0 3 a.is 0.104 C OA O 0 X 0 — I— — i i ~nj' i i ( ' t~*'~ i i r 1'" i ■ i" < ox 0.1 OX OX 0.4 OX OX O.T OX OX IX 1.1 to o a 0 X 0 9 > P 0 9 L. A grafe B quos1-stream1i n i ng Figure 87. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Veneridae. a. Veneridae species. b. Veneridae morphospace (stippled) superimposed on plot for all species. 157 040 O.TE- O.TO. 04S 040 04S 040 V* • * 04S 040 —— 04E- »♦ 040 O 04S JD E 040 3 0.1*4 o.to 04S C o 040 i T 1 "" l ” — T“ T~ I t 1 T“ ““I— — r“ 04 0.1 04 04 04 04 04 O.T 04 04 14 1.1 (0 o a 040 9 > +> a « Iw B 040 0.10 quasi-stream!ining Figure 68. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Mactridae. a. Mactridae species. b. Mactridae morphospace (stippled) superimposed on piot for all species. 158 ojbo 0.79 ■ O.TO- OJS K OjU> OJBt "»--- *♦ '/ * *r- * / • 0 J0<| DM 1 ♦ . • QAO *♦ ** 0J0 O O 0J5 e 3 0 JO 0.19- 0.10 0 J* — I— — I '■ 1 T" —r— 11,1 —"1 ■ I ' 0 JO 0.1 O J OJ 0.4 0.5 0.7 fhJ 0.9 1 J 1.1 CO O a 0 JO- 9 > +3 m ® t. B 0.10- - 0J5- ojjo- I '■ " ( ' I * -1"~ i * i 1 ox 0.1 OJ ©J O X c x 0.70.4 O J 0.9 1 . 0 1 . 1 quasi-stream!ining Figure 89. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Tellinldae and Donacidae. a. Tell inidae and Donacidae species. b. Tellinldae and Donacidae morphospace (stippled) superimposed on plot for all species. 159 040 0.75 0.10 046 040 0.55 040 0.46 040 040' o n 045 £ 040 3 0.16- 0.10 046 ^ 040 -i— ™ 'i1 I — 1— I ~t— I — I— T“ 04 o.i 04 04 0.4 04 04 0.7 04 0.1 14 1.1 a o a ® > a B 040. 04 0.4 04 04 0.1 04 quasi-streamlining Figure 90. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Psammobiinae and Sanguinolari inae. a. Psammobi inae and Sanguinolari inae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 1 60 0J0 O.TS O.TO OXS 0X0 OXE OiO oxc OAO 0X6 0 JO o OXS E OXO- 3 0.1S O 0.10 -I- c 0X6 o 0 X 0 ! 1 1 — I— I — r“ T — 1— ox 0.1 ox ox 0 . 4 ox ox O.T ox 0.1 I X 1.1 V) o Q 0 X 0 B 0 X 0 0X0. o.x. O X 0.4 O X O X O.T o x quasi-streamlining Figure 91. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Solenacea. a. Solenacea species. b. Solenacea morphospace (stippled) superimposed on plot for all species. 161 0 JO O.TR O.TO OM 0JB0- OJS OM OM OM 2 OM E 3 OM 0.1E 0.10 C OM O 0 X 0 I ' I “"I"1 — ,T.. T.i.nr... - r- T" 1 r — T“ OX 0.1 OX 0 X 0.4 OJ 0J O.T 0J 0.0 143 1.1 (0 o a © > -u « ■... i i |»i f C C i i B <<♦ ... -MM— ^l.l - A quasi-streamlining Figure 92. Plot* of relative position quasi-streamlining (S) and relative position of umbo (U) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for al1 species. 162 oxo- O.TOi O.TO n n 0X0- 0XS- • 0 X 0 * OXS • • 0X0- OXE- ...... • 0 X 0 £ o x s E3 0 X 0 0.1*- *Q 0.10- n j* . o 0 4 0 09 O Q * > 4-> « L. B OX 0.1 OX ox quasi-streamlining Figure 93. Plots of relative position quasi-streamlining (S) and relative position of umbo (U) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. 163 OJO---- iE 3 C O 04) 1.1 <0 o a OJO • > +-> * B OJ OA 04 04 quasi-streamlIning Figure 94. Plots of relative position quasi-etreamlining (S) and relative position of umbo (U) for Unionoida. a. Unionoida species. b. Unionoida morphospace (stippled) superimposed on plot for all species. 164 0.704 O n OifiS' . . E 3 0 *60- k C O 0.40- CO o OXS- a O GXO- > •f— +J C 0X0- 0.15----- o.io- ^ i i i i i i I I r r 0.00 0X5 0.10 0.15 0X0 0X5 0X0 0X5 0.40 0.45 0X0 0X5 exchangeable gapage Figure 95. Plot of relative exchangeable gapage (E) and relative position of the umbo (U) for all species. xhnebe aae E ad eaiepsto f mo (U). umbo of position relative and (E) gapage exchangeable iue 6 Po o mrhsaeocpe b suid aa for taxa studied by occupied morphospace of Plot 96. Figure relative position of umbo 0.00 Qjas*$ 0.104$ 0.60 0.0 exchangeable gapage exchangeable m m m J t * * . : ; a i ► ♦ • i t : ? ? • < * ■ * |t ; s ■ ! • • t i r s . * * * * t t . j • » * * ? * : : : » * * • ? * * v ,* ! ■ * '! ‘ X v » ‘ • * . * . ■ .'■ 'I 1 , ■ . ■ , v » ■ ■ v .* ■ * ■ > 123 *•* ***; i* *•• k w*:*wv 165 xhnebe aae E ad eaiepsto fub (U).umbo of relativeposition (E) and gapage exchangeable iue 7 Ifre canlzto o mrhsae for morphospace of channelization Inferred 97. Figure relative position of umbo S X O 0.15 0 X 0 0 X 0 0 X 0 0.10 0.25 0.40 0.35 CAS O X O 0.70 0JB0 0 .55 0.65 0.80 0.75 X . O O 04 OX 0.4 OX OX 0.1 OX xhnebe gapage exchangeable 166 167 0 3 0 O.IS O.ID OM OM 0M\m OJBO OAB 0A0- O-JS- 0J0 o £1 OM E OM 3 O.IS <*- O o.to c O jOS o 0 3 0 — r— '“T ■■ — I— T“ 0 3 0.1 0 3 0 3 OA OS GO O a 0 3 0 O > ■i* O.TO ■P «S L. B «*- 030 !**» 0 3 S 030- O.IS. 0.10-> 03S-1 TT«T 0 3 0 0 3 0 0 3 S 0.10 O.IS 0 3 0 0 3 S 0 3 0 O J 0.40 0.45 0 3 0 0 31 exchangeable gapage Figure 98. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 1 6 8 0 4 0 o.n O.TO 0 4 S 0 4 0 04S- 040-> 0 4 0 040- OM- -*> O a 0 E 3 040- O.lS-t 0.10 C 0 4 0 O OM I I i . i —T OjOO OM 0.10 O.IS 0.20 041 0 4 0 0 4 0 0 4 * 0 Jto ois <0 o a 040 a> O.TO O.TO- ^ P » * « 0 4 E 040-1 0 4 E 0 4 0 0 4 * B 0 4 0 OM OM 0 4 0 i£*_ O.IS 4 o.io •■- 04*1---- T"* 0 4 0 ■ t r r T* I r i - t ~T— 040 04S 0.10 O.U 040 04* 040 04S 040 04S olo" exchangeable gapage Figure 99. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. 169 o j o 0.7* 0.70. OJ* OJO Oil. 0J0- 0 <4* OJO 0 JO O -O OJ* E 0 JO 3 0.1* 0.10 OJ* C O 0 JO ■ r - i — r- T" OJO 0.1 OJ OJ 0.4 OJ (0 O Q. 9 > e B ss8s®». !! 001 i i i i"1 i i i i i I I ■ O J O O J S 0.10 0.1* O J O O J * O J O O J * O J O 0.4* O J O O J * exchangeable gapage Figure 100. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 170 OJO O.IS 0.70 OJS *• OM OM OM OJS OJO OJS OJO Z OJS e OJO- 3 O.IS 0 .1 0 OJS- C o OJO — I I — 1 I I I 0J o O J S 0.10 O.IS O J O O J S OJO OJS OJO OJS OJO OJS to o a OJO e > +j « u g n M iiifV B r r 0 j o O J S O.'lO O.'u O J O O J S O J O O J S O J O 0 j s q j o o ^ s exchangeable gapaga Figure 101 . Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Tellinldae and Donacidae. a. Tell inidae and Donacidae species, b. Tell inidae and Donacidae morphospace (stippled) superimposed on plot for all species. 171 040 o.n- 0.10 04S 040 040. > Q4S 040- 04E 040- 2 045 E 040 3 0.1E <*- O 0.10- c 045. o~ °-°°1--- 1 I I I i T I I I I I- 71 OjOO 046 0.10 O.IS 040 04S 040 04S 040 04S 040 04S CO O a OJO « > ■t ~ +> o ■L ■: ■. ■: :■: r iyi ft : B T l k .> >:';v:W: w :w S v a ' , ' ^ m exchangeable gapage Figure 102. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Peammobilnae and Sangulnolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. i i si b b b fe 3 3 b fe b b b bfestsbbbfefe! o o p e o o o o o c _ kr b* o K • • b relative position of umho of position relative OD o o o o o o o -ji f.J -ji o o o o o o & ifesfcbfebfebfebbbfebdb Figure 103. Plots of relative exchangeable gapage (E) relative position of umbo (U) for Solenacea. a. Solena oa a a a o e a e o species, b. Solenacea morphospace (stippled) superimposed 3 plot for all species. 1 73 OJO O.IS O.TO OJS OJO 0 OJO OJS OJO OJE OJO- O J3 0 E OJO. 3 o.is- M- O o.to OJS c o OJO i — r i ■ i " 1 r i r i I OJO 0J6 0.10 O.IS OJO OJS OJO OJS OJO OJS OJO OJS CD o a OJO 9 O.IS > •r— 0.104 OJS 11 .i 0 OJO OJS OJO B OJS OJO OJS • ♦ • OJO 9• I* • • * OJS *9 0, OJO * a . o.is 4 * o.to OJS XT OJO OJO 0JOS O.'lO O.’lS OJO Ojs OJO OJS OJO OJS OJO OJS exchangeable gapage Figure 104. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 1 74 0 4 0 0.1* 0.70 046 040 046-1 040 046 -r 040 040 O A 046 E 040 3 0.15 0.10 C 046 o 040 ■ I — i “I — r— ■I 04 0.1 04 04 04 04 00 o Q. 0 > *-> 0.70- « L. B 0.10 040 045 0.10 0.15 040 045 040 045 040 045 040 0. exchangeable gapage Figure 105. Plots of relative exchangeable gapage (E) and relative position of umbo (U) for Myidae. a. Myidae species, b. Myidae morphoapace (stippled) superimposed on plot for all species. 1 75 0 3 0 0.71 0.70- 0 3 6 0 3 0 0.S6 ■ 03G- o.*e; 0.40. o 36- 030 O n 036- £ 3 030- 0.1S 0 .1 0 - C 036i o 030-- 1 "t— -I— i — I— I 03 0.1 0 3 0 3 0.4 0 3 QD O a 0 3 0 a 0.75 > 0.70 p Oil « 0 3 0 0 3 6 0 3 0 * 2 r 0 3 6 B 0.40 0 3 6 • 4 0 3 0 0*-»- >»_ 0 3 0 0.16 0.10 0 3 6 TT 0 3 0 0 3 0 0 3 6 0.10 0.1S 0 3 0 0 3 5 0 3 0 0 3 6 0 3 0 0.46 0 3 0 0. exchangeable gapage F1gure 106. Plots of relat1ve exchangeable gapage (E ) and relative position of umbo (U) for Unionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. iue 0. lt f eaie oiino ub () and (U) umbo position of relative of Plot 107. Figure eaie et f iu () o al species. all for (N) sinus of depth relative relative depth of sinus 0.1 O 0 0 _? ft V ? » 0 ^ 4 . 0 ” ' - S O “ 0 0.7 . ■ ■■ ■ ■ 0.9 j JB } O 0 ------...... JO « f 1 f t »« ------ -- _ 4 f* o * . ft* ♦ 4 * tf A. ft..^ * ftf* ) t t* ------.^ 0.1 4 . ...... ---- _____ - ---- eaie oiino umbo of position relative ------♦ ♦ ft ♦ ft ♦ ** ♦ t f , _ — . t f . — . 0.2 t t f f ^ ♦ ft _ ♦ ^ ft f ft A ft ...... • ------ft._A -•------.ft— ° .«IUQiL„4-ftv * — t t Tf |tt • |ftft 6 ftft^ ftft^ *T%ft _^„^^i^^i«tj --o- t_.^.„5^_^Sir^-^>i»«ft-jv f t ^ f f * ft ft ^ * ft V* »* tt A ° .* * 1 . * **• * . 1 * .* ° A * * * * * ; .* ... _ * —,44 4 , .— 0*3 1 * . V * * J v [ • ° ^ 0—ip *0-— — — - - - » * . « * ♦ » » ■ ■■ ■ a t f 4 » — -»— 1 iif .w*n» n * w . f i i m . » . | a — \ t * • ft . .w ..aft— ...w _. * * 0.4 * £-*++ + * - £ •** 4 t t t * ft ♦ ftft ft ftft A . A ft * ® a ♦ . ft ^ K | a O.s ------* * s jVV --- * * — 0 v ■ ...... ------.. a a . . . . *** p ... --- P ...a&. --- • • ♦ . ------4 ...... ft 0.6 ~ V .. 1 . t f ---- p _. ------ ” V r 1 --- .. x .... 0.7 .. 1 ------...... ft ------...... X O i 76 1 - - 177 0.9 0 . 6 - — ■ ';;'w ’?w ' »iYiT;‘i iiiiitiinm r^ji' i' i' i' iY r i i Y i i | 0.1 0.2 0.3 0.4 0.5 o.e relative position of umbo Figure 108. Plot of morphospace occupied by studied taxa for relative position of umbo (U) and relative depth of sinus (N). 178 0.9 0X< (0 0.7- 3 C OX- O 0.6* x: +J a 0.4- ® ® QJ3- > e 0 .2* ® L. 0 .1* o x — I— ” 1— — r— —T“ ox 0.1 ox 0.3 0.4 7!i" ox 0.7 OX relative position of umbo Figure 109. Inferred channelization of morphospace for relative position of umbo (U) and relative depth of sinus (N). 179 o.o. 0 3 0.7- •• 03 . 0 Jt‘ OA- OJ £. 0.0- +-> 0 JO 0.1 0 3 0 3 0.4 0 3 0 3 0.7 0 3 a 0) T3 ® 0.0 > OJ <0 0.7 *— * « V■»> * ■ ■■* * A*~— r ; \ *. 0 3 — — — 3 «— r-»— --- | S •« * * a s ., , * «-£—*—* ------B ... 4.v \ • / . OA t » r ---- ♦— 03 03 r * r a p B K V n" ‘ M . , - 0313 03 0.403 03 03 0.7 0 3 relative position of umbo F i gure 110. PI ots of re 1 at i ve pos i 11 on of umbo (U ) and relative depth of sinus (N) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 180 o.« CO 0.1 ox s: 0 .1 ox 0.1 a CD TD CD > +J « ♦ A- v'1' — — T t- B ox. 1 -t— *v T t* ox 0.1 OX OX 0 A O X O X 0.1 ox relative position of umbo Figure 111. Plots of relative position of umbo (U) and relative depth of sinus (N) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. 1 ©1 0.7- OJ <0 3 C OJ 0) 0 .1 <*- o O J 0.1 O J O J 0.4 O J O J 0.7 O J O J 1 J Q ® TJ 0 J- « ^ 0. * « 0. * ® T i. * / V ---- — a » i i------B 0 JO 0 J 0.1 OJ OJ OJ OJ relative poaition of umbo Figure 112. Plots of relative poeition of umbo (U) and relative depth of sinus (N) for Mactrldae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 182 o.« 04 0.7 B OJO 0.1 04 04 04 04 04 0.7 04 relative position of umbo Figure 113. Plots of relative position of umbo (u) and relative depth of sinus (N) for TelHnidae and Donacidae. a. Tellinidae and Donacidae species. b. Tell inidae and Donacidae morphospace (stippled) superimposed on plot for all species. 1 6 3 0.9 ■ 0 4 CD« 0J' D •r—<= 0 Jt- 00 0 .1. 0.1 0.4 O.T 0.9 a> > 0.0 ■U (0 0.7 £ 04 04 — i » _...... B 044 OJ OJ « AL.* . ‘ “ • —.»». >♦ i # . .‘ o ! A l . A 0.1 OJ) OJ) 0.1 O J O J 0.4 0 4 0 4 I 04 relative position of umbo Figure 114. Plots of relative position of umbo (U ) and relative depth of sinus (N) for Paammobiinae and Sanguinolariinae. a. Psammobilnae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 164 0.4- ao 3 C •r— CO t- o 04) £. 0.1 0.4 0.7 P Q. ® "D > • r P « B — - » — *- . — - v — J frrtft — . t w * «.— ft— — -— - • -f:.T" n ' , ♦ * . J * i * - < V . :.----- * * • • 0J9 OJ) 0 J 0 J 0.4 O J 0 J 0.7 OJ relative position of umbo Figure 115. Plots of relative position of umbo (U) and relative depth of sinus (N) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. 185 OJ) 0.7 0.4 co 3 C ■r <0 0.1 **- o £. 0.1 0.4 OX +J a ® -o ® > * r - ■P a ® B t ■£■»*.«.» . » • T y j r * ? # * 4 * * • * oxJl1 -»* t ,----- 1----- 1----- 1----- r— OX 0.1 OX OX 0.4 OX OX 0.7 ox relative position of umbo Figure 116. Plots of relative position of umbo (U) and relative depth of sinus (N) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 186 o.t 0 J- G.7 ■ OA- 0 .1- a 0 J 0.1 0.7 ® TJ 0.9 ® > OJ *v~ •U 7 T - - 0 0.7 0 ♦ L. ♦ * 0 J “♦— r-r* B OJ - r s " - •••• ------0.4. ...j T -J— . otfgiigr , -----*_ II* ml: * OJ OJ * ------r*7^Aj^ •------0.1 _*_5i------ O jO t* OJ 0.1 OJ OJ 0.4 OJ OJ 0.7 OJ relative position of umbo Figure 117. Plots of relative position of umbo (U) and relative depth of sinus (N) for Myidae. a. Myidae species, b . Myidae morphospace (stippled) superimposed on piot for all species. 187 o.i 0 . 4 (0 3 C (0 0.1 o ox £ 0.1 0.1 a at XJ ® 0 . 9 > 0 J •p “4T --*---- ■■ » a * 0.1 .... T a> 4 0.0 " • — »"'4~ T f ox _*.T. ___ 4 ...* __ B 4 ( • . “ •* 4 0 . 4 4 .»*♦ • ox ox 4 0.1 « N , * v£ . -..A V A ▼ ■.-,::-:-'-;^^,:>:::-v-j4 ; •■■*?*; ‘ ' "s.. o xjOj-'it^>*'••'1 v.-.^ . ■ ,-- ---, 1— O X 0 . 1 O X O X 0 .4 O X O X 0 . 1 ox relative position of umbo Figure 118. Plots of relative position of umbo (U) and relative depth of sinus (N) for Unionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. iee o.s. <0 3 C CO I*- o p a o a t o r * — TJ « > P e 0.6 0.7 quasi-stream1ining Figure 119. Plot of quasi-streamlining (5) and relative depth of sinus (N) for all species. relative depth of einus us-temiig S ad eaie et o sns (N). sinus of depth relative and (S) quasi-stream!ining Figure 120. Plot of morphospace occupied by studied taxa for taxa studied by occupied morphospace of Plot 120. Figure 0 . 0 0.2 0.1 3 0. 0.4 .5 0. 0.6 0 0.7 9 . 0 JB OJO 9 . 0 8 . 0 7 . 0 6 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 quasi-streamlining X I 1.1 169 relative depth of sinus us-temiig S ad eaiedpho sne (N). sinue ofdepth (S) relative and quasi-streamlining iue 2. nerd hneiain f opopc for morphospace of channelization Inferred 121. Figure 0.3- 0.4- OX) 0.9 0.7- X 01 . 03 . CS . 07 . IX) 0.9 X O 0.7 0.6 C.S 0.4 0.3 0.2 0.1 CXI quasl-streamlining 190 1 9 1 OJC <0 0.1 o O jO 0.0 0.1 0.2 0 S 0.4 0.S 0.6 0.1 D J 0.9 14) e > +j « B i ■ T ' ^ 1 i OS O S 0.1 0 J 0.9 14) 1.1 quasi-stream1ining Figure 122. Plots of quasi-strsamlining (S) and ralativs depth of sinus (N) for Cardiidae. a. Cardiidae species, b. Cardiidae morphospace (stippled) superimposed on plot for all species. 192 0.7 OJ- (0 3 C o J 09 <*- 0 .1- o £ ox *-> O X 0.1 O J O J 0.4 O J O J 0.7 O J O J I X 1.1 Q. ® ® 0 J > O J e ® 0.7 L. /* O J B 0J4 O J 0 J o j 4 ^ ---- 0.1 — * * * * ox ■ 1 ■ I i * 1 T — 1— ox 0.1 0 J OJ 0 j OJ O OJ J 0.7 0 J OJ IX i.i quasi-stream1ining Figure 123. Plots of quasi-stream1ining (S) and relative depth of sinus (N) for Veneridae. a. Veneridae species, b. Veneridae morphospace (stippled) superimposed on plot for all species. 193 0.1 OJ. — .. OA- •4___ D.l 4- O O X 0.1 O X O X 0.4 O J O J 0.1 O X 0.1 I X 1.1 ■O 0.9 > +J OX > a O.T • OJ !S$ B OJ 0.4 ox ■ - * - ■ - . j— • - * «-_ ox- « o wy-**4-1111 i w « 2 y * * * 0.1' -tt* i w ox j " !■■ ■ .. i , 1 , 1 1 1 1 OX O.i ox ox O J O J 0.1 O X 0.9 I X i.i quas i-stream!ining Figure 124. Plots of quasi-streamlining (S) and relative depth of sinus (N) for Mactridae. a. Mactridae species, b. Mactridae morphospace (stippled) superimposed on plot for all species. 194 0.7 OJ to £ OJ «0 0.1 *K o -C +* 0 J 0.1 O J O J 0.4 0 J 0 J 0.7 0 J O J I X 1.1 Cl O T3 ® OJ > •r- ■U 0 J « ® 0.7 k. OJ m m m OJ B OJ. OJ- 0 J ------St*- 0.14 . — li o x i— r— *— i • " i • i ■ "T"^— i— -— :— ■— r OX 0.1 OJ OJ 0 J 0 J OJ 0.7 OJ OJ IX 1.1 quasi-streamlining Figur® 125. Plots of quasi-streaml1n1ng (S) and relative depth of sinus (N) for Tellinidae and Donacidae. a. Tell inidae and Donacidae species. b. Tell inidae and Donacidae morphospace (stippled) superimposed on plot for all species. 195 o.i 0.7 « o.i *+- o OJ) 0.1 0 J 0 J 0.4 0.S 0 Jt 0.1 0 J 0.1 1J) 1.1 a> > +j 0 a l. B OJ) x.i quasi-streamli ni ng Figure 126. Plots of quasi-streamlining (S) and relative depth of sinus (N) for Psammobiinae and Sanguinolariinae. a. Psammobiinae and Sanguinolariinae species, b. Psammobiinae and Sanguinolariinae morphospace (stippled) superimposed on plot for all species. 196 0.* OD 0 > 4J "t— r*r 0 ^ V*A. .♦ . » * - s * -*—»---- V '"' * t > s V % * B 0 .1- quasi-stream1ining Figurs 127. Plots of quasi-strsaml1n1ng (S) and ralativs depth of sinus (N) for Solenacea. a. Solenacea species, b. Solenacea morphospace (stippled) superimposed on plot for all species. * 197 0.9 0.7 OJ- ® J c OJ- (0 <4- 0.1 o JC OJ +J O J 0.1 O J O J 0.4 O J O J 0.7 O J 0.9 1 J 1.1 a 9 ■O 0.9 9 > * -f— OJ ♦ « — 1 0.7 -'A—.** a* L. OJ ♦* B OJ 0 J OJ OJ * % * ♦ * * * 0.1 , _ r OJ I ’ r 1 i I ’ > ■» *T* “ 1 1 "F1 I » OJ 0.1 O J O J 0.4 O J OJ 0.7 O J 0.9 1 J 1.1 quasi-stream!ining Figure 126. Plots of quasi-stream1ining (S) and relative depth of sinus (N) for Solecurtinae. a. Solecurtinae species, b. Solecurtinae morphospace (stippled) superimposed on plot for all species. 198 o.« > c B OJ OJ OJ O.T OJ quasi-streamlining Figure 129. Plots of quasi-stream!ining (S) and relative depth of sinus (N) for Myidae. a. Myidae species, b. Myidae morphospace (stippled) superimposed on plot for all species. 1 99 0.* 0.1 « 3 C 0 J- « 4- 0.1 o +J 0.0 0.1 O J O J 0.4 O J O J 0.1 O J 0.9 I JO 1.1 a "O 0.9 9 > OJ P ■4— i*r4 « * vi 0 . 1 -9 0 4 0* OJ 4 --- 3 - r * oi' B 0.4 OJ zzzzzzSSO^^ 0-2 0.1 0.0 r * ■■p — f111! in IT 11#' » % ■ 0.0 o!T ^ o!z 0 j 0 U O J O J 0.1 O J 0 A IJ> 1.1 quasi-stream1ining Figure 130. Plots of quasi-streamlining (S) and relative depth of sinus (N) for (Jnionoida. a. Unionoida species, b. Unionoida morphospace (stippled) superimposed on plot for all species. 200 % taxa 59 49 39 29 19 9 8.1 9.2 9.3 9.4 9.5 9.6 9.7 Relative position of umbo Figure 131. Frequency of the relative position of the umbo i n the taxa studied. % Taxa 69 i------ 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 1.9 Relative depth of the sinus Figure 132. Frequency of the relative depth of the sinus in the taxa studied. 201 x taxa 35 -|--- 0.1 0.2 0.3 0.4 0.5 0.4 0.7 0.0 0.9 1.0 Quasi-stream!i ni ng Figure 133. Frequency of quasi-streamlining in the taxa studied. X taxa 100 M 40 - - 20 - ‘ 0.1 exchangeable gapage Figure 134. Frequency of exchangeable gapage in the taxa studi ed . 202 % taxa i n 20 - 0.1 0.2 0.4 0.5 0.7 0.8 1.0 permanent gapage Figure 135. Frequency of permanent gapage in the taxa studi ed. X taxa Streanliainff f n e M M t Captf* Figure 136. Frequency of the three phases predicted by the paradigm. 203 Table 1. Distribution of representatives of the bivalve families used in study in each of the three morphological phases. A family may have representatives in more than one phase or path. Shallow infaunal burrowers and quasi-streamlined forms Cardi i dae Donac i dae Hyri idae Mactridae Muteli dae Mycetopod i dae Myi dae Solecurti dae Tel 1i ni dae Unioni dae Veneri dae Intermediate phase Cardi idae Cultel1idae Mactri dae Myidae Tel 1i ni dae Solecurtidae Solenidae Permanent gape phase Myiid path Solenid path Mactridae Mactri dae Psammobi idae Psammobi idae Myidae Solenidae Cultel1idae APPENDIX A Taxa Used In Study 204 205 Table 2. Taxa Used in Study. Phylum Mollusca Class Bivalvia Subclass Paleoheterodonta Order Unionoida Superfamily Unionoidea Family Margaritiferidae Subfamily Cumber1andinae Cumber landia monodonta (Say, 1029) Subfamily Margaritiferinae Margaritifera hembeli (Conrad, 1838) margaritifera falcata (Gould, 1850) margaritifera margaritifera (L.1758) marrianae Johnson, 1983 sinuata (Lamarck, 1819) Family Unionidae Subfamily Anodontinae Alasmidonta arcula (Lea, 1838) marginata Say, 1818 undulata (Say, 1817) viridis (Rafinesque, 1820) Anodonta anatina (Linnaeus, 1758) beringiana Middendorff, 1851 californiensis Lea, 1852 cataracts cataracta Say, 1817 couperiana Lea, 1840 cygnea (Linnaeus, 1758) dariensis Lea, 1658 doliaris Lea, 1863 gibbosa Say, 1824 grandis grandis Say, 1829 i m b e d 7 7 is Say, 1829 implicate Say, 1629 Japonica Von Martens, 1874 kennerlyi Lea, 1860 lauta Von Martens, 1877 oregonensis Lea, 1838 peggyae Johnson, 1965 suborbiculata Say, 1831 teres Conrad, 1834 Arcidens confragosus (Say, 1829) Arkansia wheeleri Ortmann & Walker, 1912 Pseudanodonta comp 1 anata (Rossmassler, 1835) elongate (Holandre, 1836) Pseudodontoideus radiatus (Conrad, 1834) Simpsonaias ambigua (Say, 1825) Strophitus connasaugaensis (Lea, 1857) subvexus (Conrad, 1834) undulatus undulatus (Say, 1817) 206 Table 2. (conti nued). tennesseensis Frierson, 1927 Lasmigona complanata (Barnes, 1823) compressa (Lea, 1829) holstonia (Lea, 1838) subviridis (Conrad, 1835) Pegias fabula (Lea, 1838) Subfamily Unioninae Irtversidens Japanensis (Lea, 1859) Lanceolaria grayana grayana (Lea, 1834) Liguminaia mardinensis (Lea, 1864) Nodularia douglasiae douglasiae (Gray, 1833) Psilunio durieui (Deshayes, 1847) Unio caffer Krauss, 1848 crassus batavus Lamarck, 1819 crassus Philipsson, 17 88 pictorum (Linnaeus, 1758) terminal is Bourguignat, 1852 tigridis Bourguignat, 1852 tumidus Philipsson, 1788 turtoni (Payraudeau, 1826) Subfamily Ambleminae Canthyria spinosa (Lea, 1836) Cyclonaias tuberculata (Rafinesgue, 1820) Elliptio ahenea (Lea, 1843) area (Conrad, 1834) buck leyi (Lea, 1843) chipolaensis Walker, 1905 complanata (Lightfoot, 1786) congarea (Lea, 1831) crassidens crassidens (Lama rck, 181 ) incrassata (Lea, 1840) dariensis (Lea, 1842) dilatata (Rafinesque, 1820) dispa Ians (Wright, 1899) downiei (Lea, 1858) fisheriana (Lea, 1838) foiliculata (Lea, 1838) fuscata (Lea, 1843) hartwrighti (Wright, 1896) hopetonensis (Lea, 1838) icterina (Conrad, 1834) Jayana (Lea, 1838) lanceolate (Lea, 1827) lugubris (Lea, 1833) macmichaeli Clench & Turner, 1956 monroansis (Lea, 1643) moussoniana (Lea, 1852) occulta (Lea, 1843) pinei (Wright, 1897) purpurella (Lea, 1857) roanokensis (Lea, 1836) 207 Table 2. (conti nued) shepardiana (Lea, 1834) tetrica (Lea, 1857) tuomeyi (Lea, 1852) tryoni (Wright, 1888) waccamawensis (Lea, 1863) waltoni (Wright, 1888) Elliptoideus si oatianus (Lea, 1840) Fusconaia askewi (Marsh, 1896) barnesiana (Lea, 1838) c e n n a (Conrad, 1838) ebena (Lea, 1831) escambia Clench & Turner, 1956 flava (Rafinesque, 1820) maculate lesueuriana (Lea, 1840) maculata (Rafinesque, 1820) masoni (Conrad, 1834) ozarkensis (Call, 1887) rotulata (Wright, 1899) Lexingtonia dolabelloides (Lea, 1840) subplana (Conrad, 1837) Megalonaias boykiniana (Lea, 1840) nervosa (Rafinesque, 1820) stoll i (Von Martens, 1900) Plectomerus dombeyana (Valenciennes, 1827) Plethobasus cicatricosus (Say, 1829) cyphyus (Rafinesque, 1820) striatus (Rafinesque, 1820) Pleurobema clava (Lamarck, 1819) cordatum (Rafinesque, 1820) decisum (Lea, 1831) georgianum (Lea, 1841) gibberum (Laa, 1838) marshall i Frierson, 192 7 modicum (Lea, 1857) perovatum (Conrad, 1834) plenum (Lea, 1840) pyriforme (Lea, 1857) reclusum (Wright, 1898) rubrum (Rafinesque, 1820) sp. troschellanum (Lea, 1852) Potamida littoral is (Cuvier, 1797) Psorula psoricus (Morelet, 1851) Ouadrula apiculata apiculata (Say, 1829) aspera (Lea, 1831) speciosa (Lea, 1862) asperate (Lea, 1861) cylindrica c y 1indrica (Say, 1817) fragosa (Conrad, 1835) houstonensis (Lea, 1859) intermedia (Conrad, 1836) 208 Table 2. (continued) metanevra (Rafinesque, 1820) nodulata (Rafinesque, 1820) petrina (Gould, 1855) pustulosa mortom (Conrad, 1835) pustulosa (Lea, 1831) quadrula (Rafinesque, 1820) refulqans (Lea, 1868) rumphiana (Lea, 1852) sparsa (Lea, 1841) stapes (Lea, 1831) tuberosa (Lea, 1834) Quincuncina irtfucata (Conrad, 1834) Tritogonia verrucosa (Rafinesque, 1820) Uniomerus caroliniana (Bose, 1801) tetralasmus (Say, 1831) Subfamily Lampsilinae Actinonaias ligamentina carinata (Barnes, 1823) 7igamentina ligamentina (Lam., 1819) pectorosa (Conrad, 1834) Cyprogenia aberti (Conrad, 1850) stegaria (Rafinesque, 1820) Cyrtonaias tampicoons is (Lea, 18 38) Dromus dromas (Le a , 1834) Ellipsaria 7Tneo7ata (Rafinesque, 1820) Epioblasma capsaeformis (Lea, 1834) penita (Conrad, 1834) personata (Say, 1829) rangiana (Lea, 1839) toru7osa torulosa (Rafinesque, 1820) triquetra (Rafinesque, 1820) GJebula rotundata (Lamarck, 1819) Gonidea anguJata (Lea, 1838) Lampsilis altilis (Conrad, 1834) australis Simpson, 1900 cariosa (Say, 1817) crocata (Lea, 1841) dolabraeformis (Lea, 1838) fasciola Rafinesque, 1820 fullerkati (Johnson & Clarke, 1984) higginsi (Lea, 1857) ornata (Conrad, 1835) ovata (Say, 1817) radiata 7uteo7a (Lamarck, 1819) radiata (Gmelin, 1791) rafinesgueana Frierson, 192 7 reeviana reeviana (Lea, 1852) splendida (Lea, 1838) straminea claibornensis (Lea, 1838) teres anodontoides (Lea, 1831) ventricosa (Barnes, 1823) virescens (Lea, 1858) 209 Table 2. (continued) Lemiox rimosus {Rafinesque, 1831) Leptodea ochracea (Say, 1817) Ligumia nasuta (Say, 1817) recta (Lamarck, 1819) subrostrata (Say, 1831) Medionidus acutissimus (Lea, 1831) conradicus (Lea, 1834) parvulus (Lea, 1860) s impsonianus Walker, 1905 walkeri (Wright, 1897) Obi iquaria reflexa Rafinesque, 1820 Obovaria olivaria (Rafinesque, 1820) Potami lus alatus (Say, 1817) capax (Green, 1832) coloradoensis (Lea, 1856) purpuratus (Lamarck, 1819) Ptychobranchus fasciolaris (Rafinesque, 1820) Jonesi (van der Schalie, 1934) occidentalis (Conrad, 1836) subtentum (Say, 1825) Toxolasma cromwe 1 1 i i {Lea, 1865) mearnsi (Simpson, 1900) paulus (Lea, 1840) pul lus (Conrad, 1838) texasensis (Lea, 1857) Truncilla donaciformis (Lea, 1827) macrodon (Lea, 1859) truncata Rafinesque, 1820 Venustaconcha el 1ipsiformis el 1ipsiformis (Conrad, 1834) el 1ipsiformis pleasi (Marsh, 1891) Villosa amygdala (Lea, 1843) choctawensis Athearn, 1964 constricts (Conrad, 1838) fabalis (Lea, 1631) iris iris (Lea, 1829) lienosa (Conrad, 1834) ogeecheensis (Conrad, 1849) ortmanni (Walker, 1925) perpurpurea (Lea, 1861) subangulata (Lea, 1840) taeniata punctata (Lea, 1865) taeniata (Conrad, 1834) trabalis (Conrad, 1834) umbrans (Lea, 1857) vanuxemi (Lea, 1838) vibex (Conrad, 1834) villosa (Wright, 1898) Family Mycetopodidae Anodontitee depexus (Von Martens, 1900) leotaudi Guppy, 1864 210 Table 2. (continued) moricandi (Lea, 1860) patagonicus (Lamarck, 1819) tenebricosus (Lea, 1834) trapezia! is (Lamarck, 1819) trigona (Spix, 1827) Leila blainvi 1 lei ana (Lea, 1834) escula (d’Orbigny, 1835) Monocondylaea minuana (d’Orbigny, 1835) Mycetopoda legumen (Von Martens, 1888) pitieri Marshall, 1927 siliquosa (Spix, 1827) Family Hyriidae Alathyria pertexta Iredale, 1934 Casta 7ia ambigua (Lamarck, 1819) pectinatus (Spix, 1827) Cucumerunio novaehollandae (Gray, 1834) Diplodon charruanus (d’Orbigny, 1835) chi lens is (Gray, 1828) granosus (Brugui6re, 1792) iheringi (Simpson, 1900) paranensis (Lea, 1834) patagonicus (d’Orbigny, 1835) Hyria corrugate Lamarck, 1819 Lortiella froggotti Iredale, 1934 rugata (Sowerby, 1868) Prisodon syrmatophorus (Meuschen, 1781) Velusunio angasi (Sowerby, 1867) Fami1y Mute1idae Aspatharia comp 1 anata (Jousseaume, 1886) rubens (Lamarck, 1819) sp. wahlbergi (Krauss, 1848) Iridina ovata Swainson, 1823 spekii Woodward, 1859 Mutela a lata (Lea, 1664) dubia (Gmelin, 1793) emini (Von Martens, 1897) hirundo (Von Martens, 1881) rostrata (Rang, 1835) Subclass Heterodonta Order Veneroida Superfamily Cardioidea Family Cardiidae Subfamily Cardiinae Acanthocardia aculeata (Linneaus, 1767) echinata (Linneaus, 1758) paucicostata (Sowerby, 1839) tuberculata (Linneaus, 1758) Parvicardiurn nodosum (Turton, 1822) Plagiocardium setosum (Redfield, 1646) 21 1 Table 2. (continued) Subfamily Fraginae Americardia biangulata (Broderip & Sowerby, 1829) guanacastens is (Hertlein & Strong, 1947 ) CorcuJum cardissa (Linneaus, 1758) Fragum fragum (Linneaus, 17 58) retusa (Linneaus, 1758) subretusus (Sowerby, 1841) tumorifera (Lamarck, 1819) unedo (Linneaus, 17 58) Trigoniocardia granifera (Broderip & Sowerby, 1829) obovalis (Sowerby, 1833) Subfamily Laevicardiinae Cerastoderma edule (Linneaus, 17 58) glaucum (Brugui6re, 1789) Clinocardium ciliataum (Fabricius, 1780) fucanum (Dali, 1907) nuttallii (Conrad, 1837) Dinocardium robustum vanhyningi Clench & Smith, 1944 Fulvia aperta (Bruguifcre, J789) mutica (Reeve, 1844) Laevicardiurn elatum (Sowerby, 1833) elenense (Sowerby, 1840) laevigatum (Linnaeus, 1758) mortoni (Conrad, 1830) norvegicum (Spengler, 17 99) oblongum (Gmelin, 1791) pictum (Ravenel, 1861) substriatum (Conrad, 1837) sybariticum (Dali, 1886) undatopictus (Nomura & Niino, 1940) Subfamily Protocardiinae Nemocardium beechei (Reeve, 1847) lyratum (Sowerby, 1841) peramabile (Dali, 1881) Subfamily Trachycardiinae Papyridea so Ternformis (Bruguidre, 1789) sp. Trachycardiurn belcheri (Broderip & Sowerby, 1829) compunctatum Kira, t962 consors (Sowerby, 1833) egmontianum (Shuttleworth, 1856) flavum (Linnaeus, 1758) magnum (Linnaeus, 1758) muricatum (Linnaeus, 1758) panamense (Sowerby, 1833) procerum (Sowerby, 1833) pseudolima (Lamarck, 1819) Quadragenarium (Conrad, 1837) reevianum (Dunker, 1852) 212 Table 2. (continued) senticosum (Sowerby, 1833) Vasticardium arenicolum (Reeve, 1845) asiaticum (Bruguifcre, 1792) burchardi (Dunker, 1877) enode (Sowerby, 1840) Superfamily Hactroidea Family Mactridae Subfamily Lutrariinae Lutraria lutraria (Linnaeus, 1758) magna (da Costa, 17 78) Tresus nuttalli (Conrad, 1837) Subfami 1y Mactri nae Mactra antiquaria (Spengler, 1802) australis Lamarck, 1818 californica Conrad, 1837 chinensis Phillipi, 1846 contraria Deshayes, 1854 corallina (Linnaeus, 1758) crotacea (Angas, 1867) discors Gray, 1837 dissimi 1 is Deshayes, 1854 dolabriformis (Conrad, 1867) elongate Quoy A Gaimard, 1835 eximi a Deshayes, 1853 fragilis Gmelin, 1791 glabrata Linnaeus, 1767 maculata Gmelin, 1791 nitida Gme1in, 17 91 ornata Gray, 1836 rufescens Lamarck, 1818 vanattae Pilsbry & Lowe, 1932 veneriformis Deshayes, 1853 williamsi Berry, 1960 Mulinia exoleta Gray, 1837 pallida (Broderip & Sowerby, 1829) Scissodesma spengleri (Linneaus, 1767) Spisula aequilateralis (Deshayes, 1854) falcata (Gould, 1850) hemphi 11i (Da11, 1694) nicobarica (Gmelin, 1791) planulata (Conrad, 1837) polynyma (Stimpson, 1860) sacha1inensis Schrenck, 1862 solidissima (Dillwyn, 1817) subtruncata (da Costa, 1778) Subfamily Pteropsel1inae Anatina anatina (Spengler, 1802) plicate! la (Lamarck, 1835) Subfamily Zenatiinae Resania lanceolate Gray, 1852 213 Table 2. (continued) Zanatia acinacas (Quoy & Gaimard, 1835) Superfamily Solenoidea Family Cultellidae Ensis arts is (Linnaeus, 17 58) minor Dal 1, 1900 myrae Berry, 1953 siliqua (Linnaeus, 1758) Phaxus attenuatus (Dunker, 1862) cultallus (Linnaeus, 1758) Siliqua costata Say, 1822 patula (Dixon, 1789) pulchalla (Dunker, 1852) Fami1y Solenidae Solan capansis Fischer, 1887 grandis Dunker, 1862 rosacaus Carpenter, 1864 rudis (Adams, 1852) sicarius Gould, 1850 strictus Gould, 1861 vagina Linnaeus, 1758 Superfamily Tellinacea Family Donacidae Amphichaana kindarmanni (Phi 1i ppi, 1847) Donax aspar Hanley, 1845 californicus Conrad, 183 7 carinatus Hanley, 1843 contusus Reeve, 1854 cultar Hanley, 1845 cunaatus Linnaeus, 1758 daltoidaus (Lamarck, 1818) danticulatus Linnaeus, 1758 gouIdi Dal 1, 1921 mancoransis Olsson, 1961 navicula Hanley, 1845 panamansis Philippi, 1849 punctostriatus Hanley, 1843 sarra Rbding, 1798 striatus Linnaeus, 1767 trunculus Linneaus, 1758 vittatus (da Costa, 1778) Fami1y Psammobi i dae Subfamily Psammobiinae Asaph is daflorata (Linnaeus, 1758) violescens (Fbrskal, 1775) Gari anomala (Deshayes, 1855) californica (Conrad, 1849) daprassa (Pennant, 1777) farvansis (Gmelin, 1791) halenae Olsson, 1961 214 Table 2 . (continued) hosoyai Habe, 1961 radiata (Linnaeus, 1758) stangeri (Gray, 1843) truncata (Linnaeus, 1758) Heterodonax bimaculatus (Linnaeus, 1758) Subfamily Sanguinolariinae Nuttallia nuttallii (Conrad, 1837) so 1 ida (Reeve, 1857 ) S a n q u m o Jar ia b i radiata (Wood, 1815) diphos (Linnaeus, 1771) nitida (Gray, 1843) Subfamily Solecurtinae Pharus legumen (Linnaeus, 1758) Solecurtus divaricatus (Lischke, 1869) scopulus (Turton, 1822) stngillatus (Linneaus, 17 58) Tagelus affinis (C.B.Adams, 1852) californianus (Conrad, 1837) divisus (Spengler, 1794) plebaius (Lightfoot, 1786) subteres (Conrad, 1837) Family Seme1idae Cumingia Tamellosa (Sowerby, 1833) Scrobicularia plana (da Costa, 1778) SemeJe crenulata (Sowerby, 1853) dacisa (Conrad, 1837) elliptica (Sowerby, 1832) pacifica Dali, 1915 proficua (Pulteney, 1799) Family Tellinidae Subfamily Macominae Macoma balth'ca (Linnaeus, 17 58) brevifrons (Say, 1834) bruguiari Hanley, 1844 constricta (Brugui6re, 1792) cumana (da Costa, 1778) indentata Carpenter, 1864 inquinata (Deshayes, 1855) nasuta (Conrad, 1837) secta (Conrad, 1837) Psammotrata obesa (Deshayes, 1855) viridotincta (Carpenter, 1856) Subfamily Tellininae Cyclotallina rami as (Linnaeus, 1758) Scrobicularia plana (da Costa, 17 78) Scutarcopagia Jinguafalis (Linnaeus, 1758) scobinata (Linnaeus, 1758) Strigi na chroma Salisbury, 1934 psaudocarnaria Boss, 1969 TeJJidora burnati (Broderip & Sowerby, 1829) cristata (R6cluz, 1842) e 2. (continued) Tellina alternate Say, 1022 crassa Pennant, 1777 cumingii Hanley, 1044 diaphana Deshayes, 1655 dispar Conrad, 1037 donacina Linnaeus, 175S idae Dal 1, 1091 incarnata Linnaeus, 17 50 inflate Gmelin, 1791 7 t 7 7ana Ireda1e , 1915 lineata Turton, 1819 listeri Rbding, 1790 7utea Wood, 1020 madagascarensis Gmelin, 1791 magna Spengler, 17 98 oval is (Sowerby, 1829) perrieri Bertin, 1841 planata Linnaeus, 1750 radiata Linnaeus, 1758 tenuis da Costa, 1778 versicolor DeKay, 1843 virgata Linnaeus, 17 58 Zearcopagia discula (Deshayes, 1855) Superfamily Veneroidea Family Veneridae Subfami 1y Chioninae Bassina calophylla (Philippi, 1836) pauciphylla (Jonas, 1839) yatei (Gray, 1835) Chi one californiensis (Broderip, 1835) fluctifraga (Sowerby, 1853) mariae (d’Orbigny, 1846) pul icaria (Broderip, 1835) pygmaea (Lamarck, 1818) subimbricata (Sowerby, 1835) subrugosa (Wood, 1828) undate 11 a (Sowerby, 1835) Humi lari a kennerleyi (Reeve, 1863) Mercenaria mercenaria (Linneaus, 1758) Protothaca asperrima (Sowerby, 1835) Columbians is (Sowerby, 1835) crassicosta (Deshayes, 1835) ecuadoriana (Sowerby, 1835) g r a t a (Say, 1830) s t a m i n e a (Conrad, 1837) t e n e r r i m a (Carpenter, 1857) zorritensis (Olsson, 1961) Subfamily Circinae Circe callipyga (Born, 1778) corrugate (Deshayes, 1853) 216 Table . (continued) intermedia (Reeve, 1863) lentiginosa (MPrch, 1853) scripta (Linnaeus, 17 58) Gafrarium pectinatum (Linnaeus, 1758) tumidum RPding, 1798) Subfami 1y Clementini inae Compsomyax subdiaphanus (Carpenter, 1864) Subfamily Cyclininae Cyclinella Jadisi Olsson, 1961 sinensis Gmelin, 1791 singleyi Dali, 1902 tenuis (R6cluz, 1852) Subfamily Dosininae Dosina anus (Philippi, 1848) bilunulata (Gray, 1838) discus (Reeve, 1850) dunkeri (Philippi, 1844) elegans Conrad, 1843 exoleta (Linnaeus, 1758) japonica (Reeve, 1850) juveni 1 is (Gmelin, 1791) lupina (Linnaeus, 17 58) ponderosa (Gray, 1835) subrosea (Gray, 1835) troscheli (Lischke, 1873) Subfamily Meretricinae Meretrix lamarcki (Deshayes, 1835) lusoria (Rbding, 1798) meretrix (Linnaeus, 1758) Tivela argentine (Sowerby, 1835) bryonensis (Gray, 1838) planulata (Broderip & Sowerby, 1829) stultorum (Mawe, 1823) triple (Linnaeus, 1777) Transennella modesta (Sowerby, 1835) Subfamily Pitarinae Ami ant is callosa (Conrad, 1837) Callista nimbosa (Lightfoot, 17 86) Megapitaria aurantiaca (Sowerby, 1831) squalida (Sowerby, 1835) Pi tar concinnus (Sowerby, 1835) consanguineus (Adams, 1952) helenae Olsson, 1961 hoffstetteri Fischer-Piette, 1969 tortuosus (Broderip, 1835) unicolor (Sowerby, 1835) vulneratus (Broderip, 1835) Saxidomus nuttalli Conrad, 1837 Subfamily Sunettinae Sunetta menstrual is (Menke, 1843) vaginal is (Menke, 1843) 21 7 Table 2. (continued) Subfamily Tapetinae Gomphina meleagris (Gmelin, 1791) Katelysia peronii (Lamarck, 1810) scalarina (Lamarck, 1818) Marchia hiantina (Lamarck, 1818) Japonica (Gme1i n, 1791) Paphia crassisuJca (Lamarck, 1818) euglypta (Philippi, 1847) gal lus (Gme11n , 17 91) schnelliana (Dunker, 1865) vernicosa (Gould, 1861) Tapes aurea (Gmelin, 1791) bicolor (Lamarck, 1791) decussatus (Linnaeus, 1758) dorsatus (Lamarck, 1758) exasperatus (Philippi, 1847) largillierti (Philippi, 1847) literatus (Linnaeus, 17 58) phi 1 ippinarum (Adams & Reeve, 1850) rhomboides (Pennant, 1777) Venerupis corrugata (Gmelin, 1791) foveolata (Sowerby, 1853) pullastra (Montagu, 1803) Subfamily Venerinae Circompha1 us strigi11inus (Dali, 1902) Periglypta multicostata (Sowerby, 1835) listeri (Gray, 1838) puerpera (Linnaeus, 17 58) Ventricolaria rugatina (Heilprin, 1887) Venus lame!laris Schumacher, 1817 verrucosa Linnaeus, 17 58 Family Petricolidae Petricola denticulate (Sowerby, 1834) Superfamily Myoidea Fami1y Myidae Subfamily Cryptomyinae Cryptomya californica (Conrad, 1837) Subfamily Myinae Mya arenaria Linnaeus, 1758 truncate Linnaeus, 1758 Platyodon cancellatus (Conrad, 1837) Family Corbulidae Subfamily Corbulinae Corbula amethystine Olsson, 1961 luteola Carpenter, 1864 APPENDIX B Calculated Values of Parameters 2 1 8 219 Table 3. Calculated values for the parameters used in thi s study. P - relative permanent gape; E relative exchangeable gape: N - relative depth of pal 1ial sinus; U - relative position of the umbo; S - quasi- streamlining . A1 1 levels are arranged in strict alphabetical order. Taxa PE S NU Cardi idae Acanthocardia aculeata 0.00 0.00 0. 50 0.14 0.40 Acanthocardia echinata 0.02 0 .00 0.49 0.12 0.42 Acanthocardia paucicostata 0.03 0 . 00 0. 53 0.14 0.39 Acanthocardia tuberculata 0.03 0.00 0. 50 0.09 0.41 Americardia biangulata 0.00 0.00 0.57 0.12 0 . 38 Americardia guanacastensis 0.00 0 . 00 0.46 0.10 0. 39 Cerastoderma edule 0. 00 0.00 0.61 0.14 0.42 Cerastoderma glaucum 0. 00 0.00 0. 56 0.13 0 . 33 Clinocardium ciliatum 0.00 0 .00 0. 53 0.21 0 .48 Clinocardium fucanum 0.00 0.00 0. 60 0.15 0.42 Clinocardium nuttallii 0.03 0.05 0.54 0.18 0.30 Corculum cardissa 0.00 0.00 0.01 0. 04 0. 32 Dinocardium r. vanhyningi 0.01 0 .00 0.49 0.08 0. 35 Fragum fragum 0.00 0.00 0.42 0.09 0.59 Fragum retusa 0. 00 0.00 0. 18 0. 08 0.54 Fragum subretusa 0.00 0 .00 0. 26 0.06 0.18 Fragum tumorifera 0.00 0.00 0. 35 0.09 0 . 55 Fragum unedo 0.00 0.00 0.38 0.08 0.34 Fulvia aperta 0.07 0.13 0.58 0. 09 0.43 Fulvia mutica 0.02 0.03 0.53 0.12 0.44 Laevicardium elatum 0. 02 0.00 0.45 0.13 0 . 38 Laevicardium elenense 0.00 0.00 0. 57 0.10 0.35 Laevicardium laevigatum 0.02 0.03 0.45 0. 14 0. 32 Laevicardium mortoni 0.00 0.00 0.53 0.16 0 . 36 Laevicardium norvegicum 0.01 0.00 0.61 0.14 0.28 Laevicardium oblongum 0.00 0. 00 0.47 0.11 0. 26 Laevicardium pictum 0.00 0.00 0.61 0.08 0.25 Laevicardium substriatum 0.00 0.00 0.58 0. 10 0.25 Laevicardium sybariticum 0.00 0.00 0.58 0.11 0. 36 Laevicardium undatopictus 0.00 0.00 0.52 0.10 0.40 Nemocardium beechei 0.01 0.01 0 .49 0.11 0.54 Nemocardium lyratum 0.02 0.00 0.56 0.11 0. 37 Nemocardium peramabile 0.00 0.00 0 . 72 0.07 0.43 Papyridea soleniformis 0.07 0.15 0.72 0. 28 0.41 Papyridea sp. 0.08 0.18 0.74 0.11 0.24 Parvicardium nodosum 0.00 0.00 0.65 0. 1 7 0. 39 Plagiocardium setosum 0.04 0.08 0.63 0.11 0.21 Trachycardiurn belcheri 0.00 0.00 0.35 0.13 0.48 Trachycardiurn compunctatum 0.01 0.00 0.49 0. 12 0.42 Trachycardiurn consors 0.00 0.00 0.37 0. 10 0.50 Trachycardium egmontianum 0.00 0.00 0.38 0. 16 0.55 Trachycardiurn flavum 0.02 0 .00 0.42 0.17 0 .43 Trachycardium magnum 0.00 0.00 0. 38 0. 1 1 0.47 Trachycardium muricaturn 0.02 0,05 0.50 0.13 0. 42 220 Table 3. (continued) T axa P E s N u Trachycardium panamense 0.01 0 .02 0. 39 0.10 0 . 39 Trachycardium procerum 0. 01 0.02 0.37 0.13 0 .40 Trachycardium pseudolima 0.03 0.00 0 .51 0.13 0.30 Trachycardium quadragenarium 0.01 0.01 0.47 0.10 0.41 Trachycardium reevianum 0.02 0.00 0.41 0.13 0.42 Trachycardium senticosum 0.02 0.00 0.45 0.15 0.47 Trigoniocardium granifera 0. 00 0.00 0.44 0.09 0. 36 Trigoniocardium obovalis 0. 00 0.00 0.27 0. 10 0 . 44 Vasticardium arenicola 0. 00 0.00 0.48 0.12 0.46 Vepricardium asiaticum 0.00 0.00 0.45 0.12 0.42 Vasticardium burchardi 0 . 00 0.01 0 . 55 0.12 0.49 Vasticardium ©node 0.01 0.00 0. 38 0.12 0.41 C u1 tel 1i dae Ensis ensis 0. 40 0.24 0. 99 0.16 0.04 Ensis minor 0. 38 0 .44 0. 99 0. 16 0.04 Ensis myrae 0.25 0. 20 0. 99 0.11 0.05 Ensis sill qua 0.45 0.54 0.99 0.17 0.05 Phaxus attenuatus 0. 30 0.31 0. 96 0. 33 0. 25 Phaxus cultellus 0.19 0 . 31 0.96 0.28 0.17 Siliqua costata 0. 25 0. 25 0. 94 0.41 0 .27 Si 1iqua patula 0.44 0.38 0. 93 0.43 0.33 Siliqua pulchella 0. 20 0.55 0.97 0. 37 0.29 Donacidae Amphichaena kindermanni 0.02 0.09 0. 92 0.48 0 . 48 Donax asper 0. 00 0.00 0. 66 0.10 0. 52 Donax californicus 0. 00 0 .00 0.86 0.35 0.61 Donax carinatus 0.00 0.00 0.83 0. 30 0 . 65 Donax contusus 0.00 0.00 0.86 0. 36 0.55 Donax culter 0. 00 0.00 0.86 0.39 0.64 Donax cuneatus 0.00 0.00 0.81 0.66 0.74 Donax deltoideus 0.01 0.00 0. 78 0.43 0.48 Donax denticulatus 0.00 0.00 0.71 0.31 0.64 Donax gouldi 0 . 00 0.00 0.77 0.41 0. 70 Donax mancorensis 0 . 00 0.00 0.77 0.28 0. 64 Donax navicula 0 . 00 0.00 0.87 0.24 0.58 Donax panamens i s 0. 00 0.00 0. 74 0.32 0,63 Donax punctostriatus 0. 00 0.00 0.75 0.45 0 . 58 Donax serra 0.02 0.00 0.80 0 .46 0.59 Donax striatus 0.00 0.00 0.77 0. 30 0 . 65 Donax truncu1 us 0. 00 0.00 0. 83 0.43 0.68 Donax vittatus 0.00 0.00 0.83 0.43 0.57 Hvri idae Alathyria pertexta 0.00 0.00 0.64 0.00 0 . 27 Castalia ambigua 0.00 0,00 0.69 0.00 0.18 Castalia pectinatus 0 . 00 0.00 0. 76 0.00 0.34 Cucumerunio novaehollandiae 0 . 00 0.00 0.92 0 . 00 0.18 Diplodon charruanus 0 . 00 0.00 0. 79 0.00 0.24 Diplodon chilensis 0.00 0.00 0.83 0.00 0.20 Diplodon granosus 0.00 0.00 0.85 0.00 0. 23 221 Table 3. (continued) T axa PE S N U Diplodon iheringi 0.00 0.00 0.72 0.00 0. 24 Diplodon paranensis 0 .00 0 . 00 0.86 0.00 0. 20 Diplodon patagonicus 0.00 0.00 0.84 0.00 0.14 Hyria corrugate 0.00 0.00 0.84 0.00 0.21 Lortiella froggotti 0.00 0.00 0.88 0.00 0.29 Lortiella rugata 0.00 0.00 0.89 0.00 0.17 Pri sodon syrmatophorus 0.00 0.00 0.71 0.00 0.31 Velusunio angasi 0.00 0.00 0.85 0.00 0.21 Mactridae Anatina anati na 0.04 0.11 0.71 0.43 0.45 Anatina pii catel1 a 0. 00 0.06 0.64 0.46 0. 32 Lutraria lutraria 0.19 0.13 0. 82 0.58 0. 35 Lutraria magna 0 . 33 0.01 0.84 0.66 0. 26 Mactra anti quaria 0.01 0.04 0. 56 0.21 0. 34 Mactra australi s 0.01 0.01 0. 78 0.25 0.52 Mactra cali forni ca 0.01 0.02 0. 83 0.30 0.44 Mactra chi nensi s 0. 02 0.00 0.68 0.37 0.47 Mactra contrari a 0.01 0.00 0.69 0.39 0.47 Mactra coral 1i na 0.01 0.00 0.67 0.24 0.44 Mactra cretacea 0.00 0.00 0. 62 0.20 0. 38 Mactra di scors 0.01 0.00 0.63 0.30 0. 37 Mactra dissimil1 is 0.01 0.00 0.66 0.38 0.40 Mactra dolabri formi s 0.06 0.04 0. 78 0.48 0.48 Mactra e 1ongata 0.01 0.00 0. 74 0.50 0. 39 Mactra ex imi a 0.01 0.00 0. 63 0.33 0.40 Mactra fragi1 is 0.12 0.00 0. 74 0.47 0.47 Mactra glabrata 0.05 0.00 0. 68 0.36 0. 32 Mactra macu1ata 0.01 0.01 0. 65 0.30 0. 38 Mactra ni ti da 0.00 0.00 0. 64 0.13 0.42 Mactra ornata 0.02 0.00 0. 69 0.35 0.46 Mactra rufescens 0.01 0.00 0.66 0. 33 0.42 Mactra vanattae 0.02 0.03 0.81 0.31 0.51 Mactra vener i formi s 0.00 0.00 0. 53 0. 27 0.48 Muli ni a exoleta 0.01 0.03 0. 70 0.31 0.43 Muli ni a pal 1i da 0.00 0.00 0. 65 0.27 0.39 Resania 1anceolata 0. 26 0.20 0. 94 0. 30 0. 53 Scissodesma spengleri 0 .03 0 .00 0.68 0.42 0.39 Spi su1 a aequi1aterali s 0.01 0.00 0.60 0.04 0.42 Spi sula falcata 0 . 03 0.00 0. 80 0 . 45 0.42 Spi sula hemphi1i 0.05 0.00 0.71 0.41 0.45 Sp i su1 a n i cobari ca 0.03 0.12 0. 70 0.51 0. 30 Spisula planulata 0.00 0.00 0. 72 0.41 0.51 Spi sula polynyma 0.04 0.02 0. 78 0.44 0. 52 Spi sula sachalinensis 0.02 0.03 0. 58 0. 38 0. 35 Spi sula solidissima 0.04 0.00 0.71 0.35 0.47 Spi sula subtruncata 0.00 0.00 0.61 0.17 0.37 T resus nuttal1i 0.00 0.00 0.73 0.61 0. 34 Zenati a ac i naces 0.40 0.52 0.89 0.05 0.20 222 Table 3. (continued) Taxa P E s N U Maraantifertdfle Cumberland!a monodonta 0.00 0.00 0. 92 0.00 0.19 Margari ti fera hembeli 0. 00 0. 00 0. 86 0.00 0.21 Margaritifera m. falcata 0.00 0.00 0. 87 0.00 0. 25 Margari ti fera m . margarlti fera 0.00 0.00 0.88 0.00 0 . 22 Margaritifera marrianae 0.00 0.00 0.87 0.00 0. 23 Margaritifera sinuata 0. 00 0.00 0.84 0.00 0. 20 Mutelidae Aspathari a complanata 0.00 0.00 0.85 0.00 0. 36 Aspathar i a rubens 0 .00 0.00 0.83 0.00 0. 24 Aspatharia sp. 0.00 0.00 0.87 0. 00 0 . 27 Aspatharia walhbergi 0.00 0.00 0.86 0. 00 0.30 Iridina ovata 0.07 0.00 0 . 79 0 . 00 0. 32 Iridina spekii 0.12 0.00 0. 87 0.00 0.19 Mute 1 a alata 0.13 0.00 0.85 0.00 0. 23 Mutela dubia 0.13 0.00 0.90 0.00 0.29 Mutela emini 0.19 0.00 0. 90 0.00 0. 27 Mutela hirundo 0. 13 0.00 0. 95 0.00 0. 28 Mutela rostrata 0. 19 0.00 0.93 0.00 0. 27 MvcetODOd i dae Anodonti tes depexus 0.00 0.00 0.81 0.00 0.28 Anodonti tes 1eotaudi 0.00 0 . 00 0. 75 0.00 0. 22 Anodont i tes mor i cand i 0. 00 0.00 0. 85 0.00 0.21 Anodontites patagonicus 0.00 0.00 0. 79 0.00 0 . 25 Anodontites tenebricosus 0.00 0.00 0.84 0.00 0. 29 Anodontites trapezialis 0.00 0.00 0.77 0. 00 0. 28 Anodonti tes tri gona 0.00 0.00 0.82 0.00 0.20 Leila blainvilleiana 0.17 0.00 0.77 0.14 0.17 Lei 1 a escu1 a 0.10 0.00 0. 73 0.12 0.31 Monocondy1aea minuana 0.00 0.00 0.73 0.00 0.30 Mycetopoda legumen 0.09 0.00 0.94 0.00 0.22 Mycetopoda pitieri 0.12 0.00 0.93 0.00 0.23 Mycetopoda si 1iquosa 0.00 0.00 0.94 0.00 0.26 Myidae Corbula amethsytina 0.00 0.00 0. 69 0.00 0.44 Corbula luteola 0.00 0.00 0. 79 0 .00 0 .45 Cryptomya californica 0.11 0.11 0. 78 0, 25 0. 57 Mya arenaria 0.15 0.15 0.83 0. 54 0. 52 Mya truncata 0.43 0.00 0. 76 0. 52 0.48 P 1 atyodon cance11atus 0.05 0.22 0. 70 0.47 0.34 Psammobi idae Asaphis deflorata 0.00 0.01 0. 76 0.51 0.42 Asaphis violescens 0.00 0.02 0. 76 0.50 0. 37 Gari anomala 0.01 0.12 0.87 0.51 0.53 Gari californica 0.06 0.08 0. 78 0.51 0.42 Gari depressa 0.00 0.12 0.86 0.56 0.42 Gari fervensis 0.00 0.04 0.85 0.56 0.46 Gari helenae 0.00 0.11 0.83 0.56 0.46 Gari radiata 0.00 0.07 0. 90 0.50 0.46 223 Table 3. (continued) T axa p E S N U Gari stangeri 0.02 0.04 0.83 0.59 0.42 Gari truncata 0.01 0.04 0.84 0.38 0. 50 Hete rodonax b i macu1atus 0. 00 0.00 0. 69 0.56 0. 50 Nuttallia nuttallii 0 .00 0.09 0.83 0. 76 0. 39 Nuttallia solida 0.00 0.03 0. 73 0. 54 0. 32 Pharus legumen 0.69 0. 23 0. 98 0.27 0.66 Sanguinolaria biradiata 0.00 0.08 0. 84 0. 65 0.44 Sanguinolaria diphos 0.00 0.19 0.82 0.66 0.43 Sanguinot aria nitida 0.01 0.30 0.91 0.56 0.46 Solecurtus divaricatus 0.82 0.05 0. 90 0. 65 0. 43 Solecurtus scopu1 us 0. 88 0.13 0.89 0.69 0. 38 Solecurtus strigillatus 0.12 0 . 28 0. 88 0.55 0.42 Tage 1 us aff inis 0.37 0.03 0 . 93 0.51 0. 56 Tagelus californianus 0. 32 0.09 0. 92 0 . 44 0 . 54 Tagelus divisus 0. 35 0. 10 0.94 0.46 0.49 Tagelus plebeius 0. 25 0.09 0. 90 0 . 53 0 . 54 Tagelus subteres 0. 35 0.06 0.93 0.41 0. 50 Solenidae Solen capensis 0. 68 0. 16 0.99 0. 34 0.03 Solen grandis 0.69 0.04 0 . 98 0 . 30 0.10 Solen rosaceus 0.63 0.38 0.98 0.12 0. 08 Solen rudis 0.44 0.43 0.97 0 . 28 0.10 Solen sicarius 0.65 0.35 0.97 0.10 0.09 Solen strictus 0.66 0.33 0 . 96 0.14 0.04 Solen vagina 0.87 0.22 0.98 0.28 0.04 Tel 1inacea Cumingia lamellosa 0.50 0.00 0.65 0.69 0.49 Cyclotellina remies 0 .01 0.01 0. 58 0. 70 0. 54 Macoma balthi ca 0.00 0.09 0. 76 0. 78 0. 50 Macoma brevifrons 0 .00 0 .05 0 .83 0.68 0.66 Macoma bruguieri 0.02 0.01 0.69 0.81 0.46 Macoma constrieta 0.00 0.06 0. 78 0.80 0.54 Macoma cumana 0.04 0.06 0. 78 0. 69 0.44 Macoma i ndentata 0.00 0.08 0.81 0.57 0. 60 Macoma inquinata 0.02 0.07 0. 73 0.83 0. 56 Macoma nasuta 0.00 0.11 0.83 0.81 0.41 Macoma secta 0.04 0.05 0.81 0. 76 0. 54 Psammotreta obesa 0.00 0.03 0.68 0.71 0. 57 Psammotreta viridotincta 0.05 0.05 0.81 0.73 0.42 Scrobicularia plana 0.03 0.03 0.77 0.67 0.51 Seme 1e crenulata 0.01 0.01 0.67 0.51 0. 57 Semele deci sa 0.01 0.01 0.66 0.71 0. 59 Semele elliptica 1 .00 0.00 0.71 0.63 0.61 Seme1e pac i f i ca 0. 50 0.00 0.73 0. 30 0. 54 Semele proficua 0.00 0.00 0.67 0.54 0. 54 Tellidora burneti 0.00 0.00 0.90 0.28 0. 36 Tellidora cristate 0.00 0.05 0.86 0.65 0.51 Tellina alternate 0.01 0.08 0.80 0. 79 0.57 Tellina crassa 0.00 0.01 0. 73 0.59 0.53 224 Table 3. (continued) Taxa P E S N U Tel 1 i na cumi ngii 0.06 0.06 0.86 0.68 0.49 Tel 1 i na diaphana 0.00 0.03 0. 73 0. 66 0.47 Tel 1 i na dispar 0.01 0.05 0. 79 0. 80 0.52 Tel 1 i na donaci na 0.00 0.07 0. 85 0.73 0 . 66 Tel 1 i an 1 dae 0.00 0.00 0.89 0.60 0.49 Tel 1 i na i ncarnata 0.04 0.06 0.81 0.73 0.48 Tel 1 i na i nf1ata 0.00 0.02 0. 68 0.59 0 . 56 Tel 1 i na 1i1i ana 0.00 0 .09 0.62 0. 74 0.50 Tel 1 i na 1i neata 0.00 0 .00 0.72 0.67 0.60 Tel 1 i na 1i steri 0.02 0.05 0.86 0. 55 0 . 50 Tel 1 i na 1 utea 0.02 0.02 0 . 86 0.58 0.42 Tel 1 i na madagascarensi s 0.02 0.02 0. 90 0. 70 0 . 50 Tel 1 i na magna 0.09 0.18 0.91 0. 55 0 .57 Tel 1 i na ovali s 0.08 0.08 0.89 0. 70 0.48 Tel 1 i na perri eri 0. 00 0.20 0. 94 0.81 0 . 54 Tel 1 i na planata 0.08 0.08 0.82 0.85 0.51 Tel 1 i na radi ata 0,01 0.01 0.89 0.21 0.41 Tel 1 i na tenui s 0.00 0.05 0.84 0.77 0.54 Tel 1 i na vers i col or 0. 00 0.00 0. 75 0. 33 0.71 Tel 1 i na vi rgata 0.04 0.04 0. 82 0. 73 0.50 Scutarcopagia linguafelis 0. 03 0.02 0. 72 0. 65 0.46 Scutarcopogia scobinata 0.00 0.01 0.67 0. 73 0.50 Strigilla chroma 0.00 0.00 0.69 0. 70 0.47 Strigilla pseudocarnea 0.00 0.00 0.69 0.79 0 .38 Zearcopagia disculus 0.06 0 .08 0.85 0.73 0.46 Unionidae Actinonaias 1. carinatus 0.00 0 .00 0.81 0.00 0. 22 Actinonaias 1. ligamentina 0.00 0.00 0.87 0.00 0 . 22 Actinonaias pectorosa 0. 00 0.00 0.60 0. 00 0.25 Alasmidonta arcula 0.00 0.00 0.67 0.00 0. 32 Alasmidonta marginata 0.00 0.00 0.85 0.00 0 . 25 Alasmidonta undulata 0.00 0.00 0.80 0.00 0.32 Alasmidonta viridis 0.00 0.00 0. 76 0. 00 0.30 Anodonta anatina 0.00 0.00 0.66 0.00 0.30 Anodonta beringiana 0.00 0.00 0.86 0.00 0.26 Anodonta californiensis 0.00 0.00 0.84 0.00 0 . 24 Anodonta c. cataracta 0. 00 0.00 0.83 0.00 0.26 Anodonta couperiana 0.00 0.00 0.80 0.00 0 . 35 Anodonta cygnea 0.00 0.00 0.66 0.00 0.25 Anodonta dariensis 0.00 0.00 0.82 0.00 0. 32 Anodonta d o 1i ar i s 0.00 0.00 0.82 0.00 0. 27 Anodonta gibbosa 0.00 0.00 0. 72 0.00 0.38 Anodonta g. grandis 0.00 0.00 0.60 0.00 0.27 Anodonta imbecillis 0. 00 0.00 0.85 0.00 0.31 Anodonta implicata 0.00 0.00 0.81 0.00 0.24 Anodonta japonica 0.00 0.00 0.78 0.00 0.36 Anodonta kennerlyi 0.00 0.00 0.89 0.00 0.22 Anodonta lauta 0.00 0.00 0.76 0.00 0.34 Anodonta oregonensis 0.00 0.00 0.86 0.00 0.28 225 Table 3. (continued) Taxa PE s N u Anodonta peggyae 0.00 0.00 0.80 0.00 0. 29 Anodonta suborbi cu1ata 0.00 0.00 0. 79 0.00 0. 35 Anodonta teres 0 . 00 0.00 0.80 0.00 0. 26 Arci dens confragosus 0. 00 0.00 0. 73 0.00 0. 30 Arkansi a wheeleri 0. 00 0.00 0.63 0.00 0. 28 Canthyria spinosa 0.00 0.00 0. 78 0.00 0.22 Cyclonaias tuberculata 0.00 0.00 0. 76 0.00 0.19 Cyprogenia aberti 0. 00 0.00 0.67 0.00 0. 36 Cyprogenia stegaria 0.00 0.00 0. 53 0.00 0. 33 Cyrtonaias tampicoensis 0.00 0.00 0. 78 0.00 0. 28 Dromus dromas 0.00 0.00 0. 70 0.00 0.17 Ellipsaria linedata 0.00 0.00 0.73 0.00 0. 14 E 11i pti o ahenea 0.00 0.00 0.88 0.00 0.19 El 1i ptio area 0.00 0.00 0 . 85 0.00 0.22 El 1iptio buckleyi 0.00 0.00 0. 84 0.00 0.24 El 1i pti o chi polaensi s 0.00 0.00 0.83 0.00 0. 22 El 1iptio complanata 0.00 0.00 0.87 0.00 0. 23 El 1iptio congarea 0.00 0.00 0.85 0.00 0.27 El 1i ptio c . crassidens 0.00 0.00 0. 73 0.00 0. 23 El 1iptio c . i ncrassata 0.00 0.00 0. 74 0.00 0. 22 El 1iptio dariensi s 0.00 0.00 0.81 0.00 0.27 El 1i ptio dilatata 0.00 0.00 0.36 0.00 0. 23 E 11i ptio di spalans 0.00 0.00 0.87 0.00 0.25 El 1iptio downiei 0.00 0.00 0. 74 0.00 0. 27 El 1iptio f i sheriana 0.00 0.00 0. 89 0.00 0.26 El 1i ptio fol1iculata 0.00 0.00 0.96 0.00 0.18 El 1iptio fuscata 0.00 0.00 0.87 0.00 0.21 El 1iptio hartwr i ghti 0.00 0.00 0.83 0.00 0.26 El 1i ptio hopetonensi s 0.00 0.00 0.83 0.00 0.30 El 1iptio icterina 0.00 0.00 0.84 0.00 0.21 El 1iptio jayana 0.00 0.00 0.88 0.00 0.29 El 1iptio 1anceolata 0.00 0.00 0.90 0.00 0.23 El 1iptio lugubris 0.00 0.00 0.80 0.00 0.25 E 11i ptio macmichaeli 0.00 0.00 0.84 0.00 0. 26 El 1iptio monroenesis 0.00 0.00 0.65 0.00 0.20 El 1i pti o moussoniana 0.00 0.00 0.81 0.00 0. 27 El 1i ptio occulta 0.00 0.00 0.80 0.00 0.21 El 1i ptio pi nei 0.00 0.00 0.90 0.00 0.21 E 11i ptio purpurel1 a 0.00 0.00 0.86 0.00 0. 20 El 1i pti o roanokensi s 0.00 0.00 0.89 0.00 0. 25 El 1iptio shepardi ana 0.00 0.00 0.97 0.00 0.15 E 11i ptio tetrica 0.00 0.00 0.86 0.00 0.25 El 1iptio tuomeyi 0.00 0.00 0.82 0.00 0.24 El 1iptio tyroni 0.00 0.00 0.84 0.00 0. 24 El 1i ptio waccamawens is 0.00 0.00 0.83 0.00 0.21 El 1i pti o waltoni 0.00 0.00 0.93 0.00 0. 24 Elliptoideue sloatianus 0.00 0.00 0.81 0.00 0. 24 Epioblasma capsaeformis 0.00 0.00 0. 76 0.00 0.21 Epioblasma penita 0.00 0.00 0.65 0.00 0.26 226 Table 3. (continued) Taxa P E s N u Epioblasma rangiana 0.00 0.00 0.76 0.00 0.37 Epioblasma t. torulosa 0.00 0.00 0.65 0.00 0.22 Epioblasma triquetra 0.00 0.00 0. 66 0.00 0. 37 Fusconai a askewi 0.00 0.00 0. 73 0.00 0.40 Fusconai a barnes i ana 0.00 0 .00 0. 78 0.00 0. 29 Fusconai a cerina 0.00 0.00 0.65 0.00 0. 23 Fusconai a ebena 0.00 0.00 0. 60 0.00 0.16 Fusconai a escambi a 0.00 0 .00 0.70 0.00 0. 32 Fusconai a f 1 ava 0. 00 0.00 0. 54 0.00 0 . 26 Fusconai a m. lesueuriana 0.00 0.00 0.78 0.00 0.15 Fusconai a m. maculata 0.00 0.00 0. 70 0.00 0.05 Fusconaia masoni 0.00 0.00 0.75 0.00 0.31 Fuscona i a ozarkens i s 0 .00 0.00 0.79 0.00 0. 25 Fusconai a rotulata 0. 00 0.00 0. 59 0.00 0 .31 Glebula rotundata 0. 00 0.00 0.71 0.00 0. 26 Gonidea angulata 0. 00 0 . 00 0.85 0.00 0. 14 Inversidens japanensis 0.00 0.00 0. 74 0.00 0.27 Lampsi1i s alti1 is 0.00 0.00 0. 78 0.00 0.31 Lampsi1i s australi s 0.00 0.00 0.85 0.00 0.20 Lamps i1i s cariosa 0.00 0.00 0.77 0.00 0. 22 Lamps i1i s crocata 0.00 0.00 0. 79 0.00 0.24 Lampsi1i s dolabriformis 0.00 0.00 0.71 0.00 0. 33 Lampsi1i s fasciola 0.00 0.00 0. 75 0.00 0. 28 Lampsi1i s fullerkati 0.00 0. 00 0.85 0.00 0. 20 Lampsi1i s higginsi 0.00 0.00 0.71 0.00 0.22 Lamps ills ornata 0. 00 0.00 0.67 0.00 0. 34 Lampsi 1 i s ovata 0.00 0.00 0.73 0.00 0.40 Lampsi1i s r. luteola 0.00 0.00 0.83 0.00 0. 22 Lampsi1i s r. radiata 0.00 0.00 0.84 0.00 0.19 Lampsi1i s rafinesqueana 0.00 0.00 0.82 0.00 0. 28 Lampsi1i s r. reeviana 0.00 0.00 0. 79 0.00 0.21 Lampsi1i s splendi da 0.00 0.00 0.77 0.00 0.27 Lampsi1i s s. claibornensis 0.00 0.00 0. 78 0.00 0.24 Lampsi1i s t. anodontoides 0.00 0.00 0.87 0.00 0. 35 Lampsi1i s ventri cosa 0.00 0.00 0.72 0.00 0.28 Lamps i1i s vi rescens 0.00 0.00 0.81 0.00 0.25 Lanceolari a g. grayana 0.00 0.00 0. 96 0.00 0.13 Lasmi gona complanata 0.00 0.00 0.82 0.00 0.27 Lasmi gona compressa 0.00 0.00 0.83 0.00 0. 34 Lasmi gona holstonia 0 .00 0.00 0.82 0.00 0. 26 Lasmi gona subvi ridi s 0.00 0.00 0.81 0.00 0. 24 Lemiox rimosus 0.00 0.00 0.72 0.00 0.21 Leptodea ochracea 0.00 0.00 0.75 0.00 0. 33 Lexingtonia dolabelloides 0.00 0.00 0.77 0.00 0.17 Lexingtonia subplana 0.00 0.00 0.78 0.00 0. 36 Ligumia nasuta 0.00 0.00 0.92 0.00 0.17 Ligumia recta 0.00 0.00 0.89 0.00 0.20 Ligumia subrostrata 0.00 0.00 0.86 0.00 0.25 Liguminaia mardinensis 0.00 0.00 0.85 0.00 0.19 227 Table 3. (continued) Taxa p E s N u Medionidus acutissimus 0..00 0..00 0., 87 0,.00 0 , 29 Medionidus conradicus 0.. 00 0..00 0..85 0,.00 0.. 26 Medionidus parvulus 0,.00 0,.00 0..86 0 ,.00 0., 29 Medionidus simpsonianus 0.,00 0.,00 0., e3 0,,00 0 .,26 Medion 1dus walker i 0..00 0., 00 0., 89 0,.00 0.. 33 Megalonaias boykiniana 0..00 0 ..00 0..73 0 ,,00 0.,21 Megalonaias nervosa 0..00 0..00 0., 77 0,, 00 0..20 Megalonai as stol1i 0., 00 0 ..00 0 .. 78 0 ,, 00 0. "0 Nodularia d. douglasiae 0., 00 0 ,,00 0.,87 0..00 0.,21 Obii quria ref 1 exa 0., 00 0 ..00 0 ,,65 0 . 00 0.. 33 Obovar i a oli var i a 0,.00 0.,00 0., 58 0 ,.00 0., 1 6 Peg i as fabu1 a 0., 00 0 .. 00 0 ., 76 0 .. 00 0.. 33 P 1ectomerus dombeyana 0.,00 0., 00 0.,87 0 ,.00 0.. 1 5 Plethobasus cicatricosus 0.,00 0.,00 0 ., 69 0,, 00 0.. 06 Plethobasus cypyhus 0.,00 0,.00 0., 72 0,,00 0,, 27 P 1ethobasus stri atus 0..00 0..00 0., 65 0,.00 0 . 14 Pleurobema clava 0,,00 0,, 00 0..73 0,.00 0.. 22 P 1eurobema cordatum 0,,00 0.,00 0., 59 0,.00 0.. 10 PIeurobema deci sum 0.,00 0..00 0.. 76 0.,00 0,, 1 7 Pleurobema georgianum 0,,00 c..00 0..77 0,.00 0..31 Pieurobema gi bberum 0..00 0..00 0..82 0,.00 0,. 33 Pleurobema marshalli 0.,00 0..00 0.,60 0,,00 0., 1 5 Pleurobema modicum 0.,00 0..00 0.. 73 0,,00 0., 26 PIeurobema perovatum 0 .,00 0,,00 0., 74 0.,00 0.,27 Pleurobema plenum 0..00 0..00 0.. 63 0..00 0., 14 Pleurobema pyriforme 0.,00 0,,00 0.,81 0.,00 0.,30 Pieurobema reelusum 0..00 0.,00 0., 78 0,,00 0.,23 Pleurobema rubrum 0..00 0.,00 0..66 0..00 0.,00 PIeurobema sp. 0.,00 0..00 0., 76 0..00 0., 32 Pleurobema troschelianum 0.,00 0..00 0.,72 0..00 0.. 18 Pomatida littoral is 0..00 0..00 0..80 0,.00 0., 24 Potamilus alatus 0.,00 0..00 0., 79 0..00 0.,23 Potamilus capax 0.,00 0..00 0..62 0,.00 0.,41 Potamilus coloradoensis 0.,00 0.,00 0.62 0.,00 0.,34 Potamilus purpuratus 0,.00 0,.00 0.,78 0,.00 0,,21 Pseudanodonta complanata 0..00 0,,00 0.,72 0,.00 0..39 Pseudanodonta elongata 0,,00 0,.00 0.,90 0,.00 0.. 24 Pseudodontoideus radiatus 0..00 0..00 0.,80 0,.00 0., 29 Psi1unio durieui 0.,00 0..00 0.,81 0,.00 0., 24 Psorula peoricus 0,.00 0,.00 0.,71 0,.00 0,,37 Ptychobranchus fascilaris 0..00 0,.00 0..89 0,.00 0..20 Ptychobranchus jonesi 0..00 0..00 0.,84 0,.00 0,, 24 Ptychobranchus occidental is 0..00 0 ,.00 0,,87 0 .00 0 ..27 Ptychobranchus subtentum 0 ,,00 0 ..00 0 ..68 0..00 0,, 24 Quadrula a. apiculata 0 ,.00 0,.00 0..66 0 ,.00 0..24 Quadrula a. aspera 0..00 0 ..00 0..59 0 ,.00 0,. 19 Quadrula a. speciosa 0 ,.00 0,.00 0 .. 74 0..00 0..37 Quadrula asperata 0 ,,00 0,.00 0.,69 0 ,.00 0,. 26 Quadrula c. cylindrica 0 ,.00 0,.00 0 ..63 0,.00 0 , 20 228 Table 3. (continued) Taxa p E s NU Quadrula fragosa 0. 00 0.00 0.59 0 .00 0 .23 Quarula houstonensis 0.00 0.00 0.64 0.00 0. 33 Quadrula intermedia 0 .00 0.00 0. 76 0.00 0. 23 Quadrula metanevra 0.00 0 .00 0.63 0.00 0 . 33 Quarula nodulata 0.00 0.00 0.61 0.00 0. 38 Quadrula petrina 0.00 0.00 0. 72 0.00 0. 39 Quadrula p. mortoni 0.00 0.00 0.60 0.00 0.44 Quadrula p. pustulosa 0.00 0.00 0.61 0.00 0. 36 Quadrula quadrula 0.00 0.00 0.66 0.00 0.40 Quadrula refulgens 0.00 0.00 0. 59 0.00 0. 34 Quadrula rumphiana 0 .00 0.00 0. 59 0.00 0.46 Quadrula sparsa 0. 00 0.00 0.72 0.00 0. 36 Quadrula stapes 0.00 0.00 0. 58 0 .00 0. 38 Quadrula tuberosa 0.00 0.00 0.65 0.00 0. 24 Qu i ncunc i na i nfucata 0.00 0.00 0. 64 0.00 0.33 Simpsonaias ambigua 0.00 0 .00 0.85 0 .00 0.21 Strophitus connasaugaensis 0.00 0.00 0.83 0.00 0. 26 Strophitus subvexus 0.00 0.00 0.77 0.00 0. 35 Strophitus u. undulatus 0.00 0.00 0.83 0.00 0.31 Strophi tus u . tennesseensi s 0.00 0.00 0.85 0.00 0.27 Toxolasma cromwelli 0.00 0.00 0.79 0.00 0. 30 Toxolasma mearnsi 0.00 0.00 0. 78 0.00 0. 25 Toxolasma paulus 0.00 0.00 0.77 0.00 0.21 Toxolasma pullus 0.00 0.00 0. 74 0.00 0. 36 Toxolasma texasensis 0.00 0.00 0. 79 0.00 0.21 Tritogonia verrucosa 0.00 0.00 0.95 0.00 0. 16 Truncilla donaciformis 0.00 0.00 0. 74 0.00 0. 38 Truncilla macrodon 0.00 0.00 0.86 0.00 0.33 Truncilla truncata 0.00 0.00 0. 70 0.00 0.35 Unio caffer 0.00 0.00 0.85 0.00 0. 23 Unio c. batavus 0.00 0.00 0.83 0.00 0.25 Unio c. crassus 0.00 0.00 0.81 0.00 0.18 Unio pictorum 0.00 0.00 0.89 0.00 0.25 Unio terminalis 0.00 0.00 0. 79 0.00 0.27 Unio tigridis 0.00 0.00 0.83 0.00 0. 15 Unio tumidus 0.00 0 .00 0.84 0.00 0. 29 Unio turtoni 0.00 0 .00 0.86 0.00 0.27 Uniomerus caroliniana 0.00 0.00 0.84 0.00 0.15 Uniomerus tetralasmus 0.00 0.00 0.85 0.00 0. 26 Venusticoncha e. e 11ipsiformis 0. 00 0.00 0.82 0.00 0. 30 Venusticoncha e. pleasi 0.00 0.00 0.81 0.00 0. 28 villosa amygdala 0.00 0.00 0.80 0.00 0. 25 V i11osa choctawens i s 0.00 0.00 0.76 0.00 0.26 Villosa constricta 0.00 0.00 0.80 0.00 0. 23 Vi 1losa fabalis 0.00 0.00 0.86 0.00 0.31 vi1losa iris 0.00 0.00 0.88 0.00 0.17 villosa lienosa 0.00 0.00 0.80 0.00 0.30 villosa ogeecheensis 0.00 0.00 0.84 0.00 0. 29 V i11osa ortmann i 0.00 0.00 0.84 0.00 0. 28 229 Table 3. (continued) T axa P E s N U villosa perpurpurea 0. 00 0.00 0.80 0.00 0.20 Villosa subangulata 0. 00 0.00 0.83 0. 00 0. 24 Villosa t. punctata 0.00 0.00 0.82 0. 00 0. 26 Villosa t. taeniata 0.00 0.00 0.83 0.00 0.28 Villosa trabalis 0.00 0.00 0.83 0. 00 0.19 V i11osa umbrans 0.00 0.00 0 .82 0.00 0.26 villosa vanuxemi 0.00 0.00 0.81 0.00 0.27 Vi 11osa vibex 0.00 0.00 0.85 0.00 0.25 v i11osa v i11osa 0. 00 0. 00 0.82 0.00 0. 24 Yenaridae Amiantis callosa 0.00 0.00 0.71 0. 30 0.16 Bassina calophylla 0.00 0. 00 0.58 0.12 0. 24 Bassina pauciphylla 0.00 0. 00 0.68 0. 38 0. 29 Bassina yatei 0.00 0.00 0 . 63 0.30 0.25 Chione californiensis 0.00 0.00 0 . 60 0. 20 0. 32 Chione fluctifraga 0.00 0. 00 0. 54 0.21 0.31 Chione mariae 0.00 0 . 00 0.69 0.22 0.32 Chione pulicaria 0.00 0.00 0.62 0. 23 0. 35 Chione pygmaea 0.00 0 . 00 0 . 72 0. 23 0. 28 Chione subimbricata 0.00 0.00 0.54 0.13 0. 16 Chione subrugosa 0 .00 0.00 0 .64 0 . 29 0.27 Chione undatella 0.00 0.00 0.61 0.11 0. 39 Circe callipyga 0.00 0.00 0 .63 0.29 0. 33 Circe corrugata 0.00 0.00 0. 67 0. 23 0.40 Circe intermedia 0 .00 0. 00 0.67 0.25 0.40 Circe lentiginosus 0.00 0.00 0.63 0.23 0. 35 Circe scripta 0.00 0.00 0. 76 0 . 22 0. 35 Compsomyax subdiaphinus 0.00 0.05 0. 74 0.48 0. 24 Cyclinella jadisi 0.00 0. 00 0.67 0 .40 0. 32 Cyclinella sinensis 0.00 0.00 0. 52 0.50 0.38 Cyclinella singleyi 0.00 0.00 0. 58 0 . 38 0. 36 Cyclinella tenuis 0.00 0.00 0.56 0 . 50 0. 35 Dosinia anus 0.00 0. 00 0.68 0.47 0.30 Dosinia bilunulata 0 .00 0.00 0.68 0.43 0.23 Dosinia discus 0.00 0. 00 0. 73 0.60 0. 33 Dosinia dunkeri 0.00 0.00 0. 59 0.43 0. 28 Dosinia elegans 0.00 0.00 0. 70 0.45 0.31 Dosinia exoleta 0 .00 0.00 0.64 0.65 0. 33 Dosinia japonica 0.00 0. 00 0.69 0 . 38 0. 29 Dosinia juvenilis 0.00 0.00 0.58 0.32 0. 28 Dosinia lupina 0.00 0.00 0.62 0.63 0. 26 Dosinia ponderosa 0.00 0.00 0.66 0.40 0. 34 Dosinia subrosea 0.00 0.00 0.65 0.51 0.29 Dosinia troscheli 0.00 0.00 0.65 0.51 0.26 Gafrarium pectinatum 0.00 0.00 0.68 0.26 0.29 Gafrarium tumidum 0 .00 0.00 0.55 0.18 0. 26 Gomphina meleagris 0.00 0.00 0. 76 0. 28 0.47 Humilaria kennerleyi 0.00 0.00 0.69 0.16 0. 24 Katelysia peronii 0.00 0.00 0.64 0.20 0. 35 230 Table 3. (continued) Taxa p E s N u Katelysia scalarina 0..00 0,.00 0,, 73 0 ,.24 0 .. 24 Catlista nimbosa 0 .. 00 0..00 0., 87 0 , 26 0.,31 Marchia hiantina r> 00 0 ,.00 0., 56 0.,41 0,.21 Marchia japonica 0., 00 0,,00 0. 67 0.,38 0., 23 Megapitaria aurantiaca 0., 00 0,.00 0. 65 0 . 27 0., 35 Megapitaria squalida 0..00 0 ..00 0.,73 0., 33 0.,27 Mercenaria mercenaria 0,,00 0,,00 0.,62 0 .,28 0.. 1 9 Meretrix lamarcki 0.. 00 0., 00 0., 72 0., 39 0. 42 Meretrix lusoria 0., 00 0..00 0.,65 0.. 1 3 0.,40 Meretrix meretrix 0 ..00 0..00 0. 68 0., 30 0.. 32 Paphia crassisulca 0 ,.00 0,.00 0 ..81 0,,48 0,. 20 Paphia euglypta 0 .. 00 0.. 00 0., 83 0., 28 0., 32 Paphia ga11 us 0,.00 0,, 00 0.,67 0..45 0 ..37 Paphia schnelliana 0 ,. 00 0 ..00 0.. 76 0..25 0., 36 Paphia vernicosa 0.,00 0,.00 0., 73 0.,31 0., 40 Periglypta chemnitzi 0.,00 0,,00 0 .59 0..28 0.. 26 Periglypta listeri 0.,00 0,,00 0..63 0.,31 0,,27 Periglypta multicostata 0.,00 0..00 0 .62 0.,20 0.. 30 Periglypta puerpera 0 ,,00 0..00 0.,59 0.,33 0..25 Petricola denticulata 0., 07 0.. 1 3 0 .81 0.. 35 0,,31 Pitar concinnus 0.,00 0..00 0..71 0..30 0,. 36 Pitar consanquineus 0..00 0.,00 0 .,60 0..30 0., 50 Pitar helenae 0.,00 0,,00 0., 66 0.,31 0., 33 Pitar hoffstetteri 0.,00 0..00 0.,63 0.. 39 0..42 Pitar tortuosus 0.,00 0.,00 0., 64 0..29 0., 33 Pitar unicolor 0,.00 0,,00 0., 70 0,,29 0 ., 33 Pitar vulneratus 0..00 0,,00 0.,57 0,.25 0..43 Protothaca asperrimus 0.,00 0.,00 0,,61 0., 29 0., 33 Protothaca columbiensis 0,.00 0,.00 0..64 0., 23 0,, 30 Protothaca crassicostata 0.,00 0.,00 0. 68 0., 24 0.. 29 Protothaca ecuadoriana 0..00 0,.00 0.,58 0..27 0.. 29 Protothaca grata 0.,00 0,.00 0.,62 0., 10 0,, 24 Protothaca stami nea 0..00 0,.00 0 .,61 0..44 0,.33 Protothaca tenerrima 0 ,.00 0..00 0.. 78 0.. 55 0..31 Protothaca zorritensis 0..00 0 ,.00 0 ..58 0 . 25 0..40 Sunneta menstrual is 0.,00 0,.00 0 ., 75 0.,31 0 ,. 33 Sunneta vaginalis 0,.00 0,.02 0,, 72 0 ,. 33 0 ..36 Tapes aurea 0,,00 0 ..00 0 ..71 0 ., 34 0 ,.31 Tapes bicolor 0 ,.00 0 .,00 0 ..83 0 ,.27 0 ,.27 Tapes decussatus 0 ,.00 0 ,.00 0 ,. 69 0 ..54 0 ,. 29 Tapes dorsatus 0 ,.00 0 ,.00 0 ,. 76 0,.37 0 ,. 22 Tapes exasperatus 0..00 0,.02 0 .,73 0 ..34 0., 30 Tapes largillierti 0..00 0,.00 0 .. 72 0 .. 39 0.. 25 Tapes literatus 0..00 0,.00 0 .,85 0 ., 33 0 ..21 Tapes phi 1ippinarum 0..00 0 ,.00 0,.73 0 ,. 33 0 ,.31 Tapes rhombo i des 0 ..00 0 ,,00 0 .,71 0 ..35 0 ., 33 Tivela argentine 0 ..00 0 ,.00 0 ..58 0 ..19 0 ,.43 Tivela bryonensis 0 ,.00 0 ..00 0 .,61 0 .. 29 0 .,44 Tivela planulata 0 ,,01 0..03 0 .. 75 0 .. 25 0,, 55 231 Table 3. (continued) T axa P E s N U Tivela stultorum 0.00 0.00 0. 74 0. 23 0 .44 Tivela tripla 0.00 0. 00 0. 54 0.64 0. 50 Transennella modesta 0.00 0. 00 0. 65 0.39 0.41 Saxidomus nuttalli o. oe 0.17 0.77 0.56 0 .40 Venerupis corrugatus 0.00 0 .07 0 . 79 0.55 0 .29 Venerupis foveolata 0.00 0.00 0.65 0.16 0. 33 Venerupis pullastris 0.01 0.02 0.68 0. 39 0. 26 Ventricolari a rugati na 0. 00 0.00 0. 53 0.21 0. 34 Venus lamellaris 0 . 00 0.00 0. 65 0.21 0.33 Venus verrucosa 0.00 0.00 0.61 0. 22 0. 24 LIST OF REFERENCES Agrel1, I. 1949. The shell morphology of some Swedish unionides as affected by ecological conditions. Arkiv for Zoologi 41(15):1-30; 14 figs.; 4 tables. Alexander, R. R. 1974. Morphological adaptations of the bivalve Anadara from the Pliocene of the Kettleman Hills, California. Journal of Paleontology 48:633-651; 12 figs.; 3 pis.; 3 tables. Allen, J. A. 1958. On the basic form and adaptations to habitat in the Lucinacea (Eulamel1ibranchiata). 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