THE FUNCTIONAL MORPHOLOGY AND ECOLOGY OF THE SPATANGOID GENUS BRISASTER GRAY by PETER EDWIN GIBBS B.Sc, University of Leicester, 1961 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in the Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April, 1963 In presenting this thesis in partial fulfilment of the requirements for an .advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that per• mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives., It is understood that copying, or publi• cation of this thesis for financial gain shall not be allowed without my written permission. Department of Zoology The University of British Columbia, Vancouver 8, Canada. Date April 1963 ABSTRACT The functional morphology, taxonomy and ecology of the Spatangoid genus Brisaster Gray (Family Schizasteridae) from Howe Sound, British Columbia, have been investigated. Brisaster predominantly inhabits a mud substratum and burrows to a depth of 1 cm., constructing both a respiratory funnel and a double sanitary apparatus. Burrowing and feeding activities resemble those of Spatangids. The absence of a sub-anal fasciole in Bri saster correlates with its shallow burrowing habit. Despite the lack of a sub-anal fasciole, the ciliary current pattern of the test is similar to that of the Spatangids which possess this fasciole. This suggests a common ancestral form (perhaps for all Spatangoids) in which the basic ciliary pattern had evolved; thus the different types of fascioles appear to have evolved as superimpositions on the basic ciliary pattern rather than the reverse. The zoogeography and taxonomy of the genus is briefly reviewed and the need"for qualification of certain taxonomic criteria stressed. The latero-anal fasciole, for example, is an unreliable taxonomic character since it disappears with growth to varying degrees in diff• erent species. This possibly reflects changes in niche since the isolation and speciation of the genus took place. Biometrical analyses of the lengths of the ambulacral petals and the test height indicate that only a single species of Bri saster is present along the west coast of North America. Formerly two species had been described. Taxonomic priority is given to the species i i i Brisaster latifrons; B. townsendi thus becomes a synonym. Synonymy is also suggested for the Japanese species B_. owstoni, in view of paleo- geographic evidence. The gonads of Brisaster do not develop until the second year and, as the ova appear to require two years to develop to maturity, the females probably first spawn in their third year. On this basis, the first, second and third (and older) year classes were identified in the populations occurring in Howe Sound. These populations showed marked differences in their size-frequency distribution but a similar age class composition. The size differences of individuals appear to correlate with differences in the population density, larger individuals being found in less crowded areas. It is suggested that these density differences are a result of the irregular settlement of a restricted pelagic larval stage. The differences in the size of individuals can therefore be related to differences in the individual growth rate. Passive interference, both inter- and intraspecific may be responsible and two possible mechanisms have been suggested. i v TABLE OF CONTENTS Page INTRODUCTION ... .. ... ... 1 CONDITIONS IN HOWE SOUND 3 MATERIALS AND METHODS 4 RESULTS 9 IA Morphology of Brisaster .. 9 IB Observations on the mode of life of Brisaster .. 12 1. Ci1iary currents 12 2. Burrowing activity 14 3. Feeding activity 15 II Biometrical analysis .. .. 16 III Ecological investigations 20 DISCUSSION .. .. 27 Morphology and mode of°life 27 Taxonomy and zoogeography 30 Ecological studies 36 SUMMARY .. .-. 43 LITERATURE CITED 46 APPENDIX 50 V LIST OF TABLES Table Page 1 Approximate numbers of the various types of tube-feet •n Brisaster, at two test lengths 11A 2 Analysis of covariance for mean lengths of anterior (II and IV) and posterior (I and V) ambulacral petals of individuals from three populations (Stations 1A, 3 and 6) used in the biometrical analysis. Data presented in Fi gure 6. .. 17B 3 Length (mean and range) of individuals, and slopes of regression lines calculated for samples of three popula• tions (Stations 1A, 3 and 6) used in the biometrical analysis .. •. 18A k Analysis of covariance for height and length of indiv• iduals from three populations (Stations 1A, 3 and 6) used in the biometrical analysis 19A 5 Analysis of covariance for area of peripetalous fasciole and size number (length x width) of individuals from two populations (Stations 3 and 6) used in the biometrical analysis. Data presented in Figure 8 208 6 Details of samples collected from stations at two depth strata - 135 and 65-75 fathoms 22A 7 Analysis of variance for length of individuals from three populations (Stations 1, 2 and 3) 23A vi LIST OF TABLES, cont'd. Table Page 8 Statistical comparison of lengths of individuals in three populations (Stations 1, 2 and 3) 23B vi i LIST OF FIGURES Figure Page 1 Chart of Howe Sound, British Columbia, showing dredging stations .. S' 2 Positions of measurements taken on the test and used in biometrical analysis. 6A 3 Main features of the test of Brisaster 9A k Course of the main ciliary currents on the test of Brisaster 12A 5 Burrowing of Bri saster in (A) lateral and (B) oral view. 13A 6 Relationship between mean lengths of anterior (II & IV) and posterior (I & V) ambulacral petals in Individuals from three populations (Stations 1A, 3 and 6) 17A 7 Relationship between the mean lengths of the anterior (II & IV) and posterior (I & V) ambulacral petals and size number (length x width). 18B 8 Comparison of the area of the peripetalous fasciole against size number (length x width) in individuals from two populations (Stations 3 and 6). 20A 9 Length-frequency of all samples collected in Howe Sound on July 12, September 10, and October k and 5, 1962. 21A vi i i LIST OF FIGURES, cont'd. Figure Page 10 Ovarian structures in Brisaster 24A 11 Percentages of size groups for ova diameters in second/ and third year (and older) females 25A 12 Length-frequency of year classes of females, as indicated by ova diameters, in three populations (Stations 1, 2 and 3). 26A I LIST OF ABBREVIATIONS USED IN FIGURE 3. a.tf. anterior sensory tube-feet al.tf. anterior lateral sensory tube-feet an. anus an.fasc. anal part of latero-anal fasciole f.gr. feeding grill of small spines fb.tf. funnel-building tube-feet g.p. gonopore lat.fasc. — lateral part of latero-anal fasciole mad. madreporite mo. mouth o.tf. -- oral feeding tube-feet peri.fasc. — peripetalous fasciole plas. plastron pl.tf. posterior lateral sensory tube-feet pp.tf. -- peri-plastronal sensory tube-feet pr.p. periproctal plates prot.s. -- protective arch of spines covering ambulac prot.s.an. .-- protective spines covering anus ps.p. peristomial plates r.tf. respiratory tube-feet san.tf. sanitary tube-fuilding tube-feet san.t.b.s. -- sanitary tube-building tuft of spines sp.s.p. spatulate spines of plastron X ACKNOWLEDGMENTS The author is indebted to Dr. Paul A. Dehnel for his advice and assistance in the planning and execution of this study. Gratitude is also expressed to Dr. Dennis H. Chitty, Dr. Cyril V. Finnegan and Dr. William S. Hoar, for their critical reading of the manuscript. The author is also indebted to Capt. Dale-Johnson and the officers and crew of the C.H.S. "Ekholi" for their skill and patience in operating the dredge, sometimes under difficult conditions. The generous and able assistance of many people, especially Mr. Thomas H. Carefoot, in the preliminary sorting of the catch on board ship is gratefully acknowledged. This study was carried out while the author Was in tenure of a N.A.T.O. Studentship given by the Department of Scientific and Industrial Research, London, England and the research was aided by grants from the National Science Foundation of the United States and the National Research Council of Canada. 1. INTRODUCTION Recently, Nichols (1959a, b), in an extensive investigation of the morphology and mode of life of the irregular echinoids, particularly the Order Spatangoida, has demonstrated the importance of a functional interpretation of those morphological characters used as taxonomic criteria. Similarity in the conspicuous features of the text, such as the fascioles, need not indicate phylogenetic affinity: the possibility of convergence in different stocks must be appreciated. Nichols1 study on the Spatangoida was confined to members of the Family Spatangidae, both living and fossil. Clearly, further investigation of other groups is necessary before the results can be extended to an elucidation of the phylogeny of the Order Spatangoida. Part of the present study, therefore, is an attempt to interpret the morphology of the genus Brisaster, a typical member of the Family Schizasteridae, in terms of its mode of life, relating also the observed morphological changes occurring during its ontogeny. Those Spatangoida grouped in the Family Schizasteridae all possess both a peripetalous and a latero-anal fasciole. Little is known about their biology, possibly because they are, typically, deep-sea inhabitants and many genera are represented only in Antarctic waters. The only representative of the Family Schizasteridae along the west coast of North America, north of the Gulf of California, is the genus Brisaster (formerly named Schizaster by Agassiz, 1898) which has a wide latitudinal distribution, extending from the Gulf of Panama (type locality) to Alaska and Japan, at depths varying from 6 to 995 fathoms.