Echinodermata: Echinoidea: Clypeasteroida: Scutellina) John M

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Gulf of Mexico Science Volume 17 Article 4 Number 1 Number 1

1999 Eccentricity of the Apical System and Peristome of Sand Dollars (Echinodermata: Echinoidea: Clypeasteroida: Scutellina) John M. Lawrence University of South Florida

Christopher M. Pomory University of South Florida

DOI: 10.18785/goms.1701.04 Follow this and additional works at: https://aquila.usm.edu/goms

Recommended Citation Lawrence, J. M. and C. M. Pomory. 1999. Eccentricity of the Apical System and Peristome of Sand Dollars (Echinodermata: Echinoidea: Clypeasteroida: Scutellina). Gulf of Mexico Science 17 (1). Retrieved from https://aquila.usm.edu/goms/vol17/iss1/4

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Eccentricity of the Apical System and Peristome of Sand Dollars (Echinodermata: Echinoidea: Clypeasteroida: Scutellina)

jOHN M. LAWRENCE AND CHRISTOPHER M. POMORY

Eccentricity, location of structures away from a central position, is associated with directional movement. Although sand dollars have directional movement, only eccentricity of the anus is apparent. Eccentricity of the apical system and peristome is less apparent. We have found the apical system and the peristome are statistically significantly slightly anterior in Mellita tenuis, Mellita quinquiesper forata, Mellita isometra, and Encope aberrans. The apical system of Leodia sexiesper forata is central and that of Echinarachnius parma is anterior, whereas the peri stome of both is statistically significantly slightly posterior. The usual selective pressure for pronounced anterior location of the mouth in animals with direc tional movement may be countered by the mode of feeding in sand dollars that utilizes the oral surface. The basis for the eccentricity of the apical system is not known.

TTnowledge of body form gives insight into ham, 1949; Raup, 1956; Alexander, 1972; Stan .ft. the biology and ecology of species. Sym ton et al., 1979; Beadle, 1995; Mooi, 1997) as metry is a major aspect of body form, and Bek sociated with its unique feeding behavior. Ac lemishev (1969) noted the wide variety that ex tual measurements of the location of the apical ists. He concluded that the origin of bilateral system and peristome are few (Woodring et al., symmetry in echinoids was clearly associated 1940; Durham, 1949; Kier, 1972; Mooi and with a fossorial mode of life and suggested re Harold, 1994; Beadle, 1995; Mooi, 1997; Ali, sistance of the particulate substrate to move 1998). ment was sufficient to make it advantageous. Raup (1956) wondered whether the varia Bilateral symmetry is usually associated with tion he found in the posteriorly eccentric api differentiation of the anterior and posterior cal system of Dendraster excentricus would be par ends of the body, with the peristome (mouth) alleled by that of the peristome. Beadle (1995) located anteriorly and the anus posteriorly reported a strong correlation between the two (Wainwright et al., 1976). In clypeasteroids, the did exist. Here we report the location of the periproct (anus) has moved out of the apical peristome and apical system in six species of system toward the posterior edge of the test scutellid sand dollars and test the hypothesis (Durham, 1966). This movement has been that the two are eccentric. thought to be adaptive because it separates the feces from the aboral respiratory structures MATERIALS AND METHODS (Bather, 1900). Smith (1984) stated "During the evolution Six species of scutellid sand dollars were of irregular echinoids there is a pronounced studied: Encope aberrans Martens, Leodia sexies tendency for the peristome to shift anteriorly.'' p1!1forata (Leske) , Echinarachnius parma (La However, this expected, pronounced anterior marck), Mellita quinquiespe1jorata (Leske), Mel location of the peristome is not present in cly lila isometra Harold and Telford, and Mellita ten peasteroids. Indeed, Mortensen (1948) stated uis Clark. Two populations of M. tenuis were that the apical system and peristome of Cly studied, one for two successive years. peasteroida usually is central. Dafni (1988) did Dimensions used for eccentricity calcula not even mention the peristome in his discus tions (see Beadle, 1995) were measured to the sion of the relation between bilateral symmetry nearest 0.1 mm with vernier calipers. Eccen and the anus. Slight eccentricity of the peri tricity of the apical system was calculated by the stome, both anterior and posterior, has been ratio used by Raup (1956), Stanton et al. reported for many species without documen (1979), and Beadle (1995): 2x/y, where xis the tation (Clark and Twitchell, 1915; Nisiyama, distance from the center of the apical system 1966). An exception is the famous pronounced to the posterior test margin and y is the test posterior eccentricity of the apical system and length. For consistency, eccentricity of the peri mouth of some Dendraster species (Clark and stome was calculated by the same ratio, where Twitchell, 1915; Woodring et al., 1940; Dur- x is the distance from the posterior edge of the

36 GULF OF MEXICO SCIENCE, 1999, VOL. 17(1)

peristome to the posterior test. Ratios > 1 in dicate anterior eccentricity; ratios <1 indicate posterior eccentricity. The means of the eccen tricity ratios for the apical system and peri stome were used to calculate whether the po

sitions of the apical system and peristome were <0 >!'l <0 IN l1'l O'l 0.--<0INOO :$2 the same (apical system ratio I peristome ratio). 000000 00 A one-sample t-test was used to test eccen cicicicicici cici tl tl tl tl tl tl tl tl tricity values for departures from 1. One-way *'l<·**•X•* OOOOO'>Oli'l.-< *.,..--< * ANOVA and the Tukey-Kramer multiple com O'l !'- .,. 00

son-Darling test and equality of variances by .,.lfllfl.--

TABLE 2. Statistical differences in the eccentricity ratios of the apical system and peristome of sand dollars. The species are ranked from the lowest to the highest ratio. Ratios > 1 indicate anterior eccentricity, = 1 no eccentricity, and < 1 posterior eccentricity. Species with the same letter do not differ significantly (P > 0.05).

Apical system Ratio Peristome Ratio

Leodia se.~iespe1jorata A 1 Echinarachnius parma A <1 Echinarachnius parma BC >1 Leodia sexiespe~forata A <1 Mellita tenuis Naples c >1 Encope abermns B >1 Encope abe/Tans CD >1 Mellita tenuis Naples c >1 Mellita tenuis Mullet Key 1996 CD >1 Mellita tenuis Mullet Key 1996 c >1 Mellita quinquiespe~forata CD >1 Mellita tenuis Mullet Key 1995 c >1 Mellita isometra D >1 Mel/ita isometra D >1 Mellita tenuis Mullet Key 1995 D >1 Mellita quinquiespe1jorata D >1

DISCUSSION edge of the peristome of the neotype of M. quinquiesperfomta is 41% not 29.9% as in Mooi The apical system of five of the six species and Harold (1994) (Mooi, pers. comm.). This of sand dollars studied here was slightly ante is equivalent to an eccentricity of 1.43, much riorly eccentric as was the peristome in four greater than the mean of 1.280 found here. species. The apical system of L. sexiesperjomta Clark and Twitchell (1915) reported slightly was central, and the peristome of L. sexiesper posteriorly eccentric peristomes have been re fomta and E. parma was posteriorly eccentric. ported for the extinct species Scutella mississip That the eccentricity ratios of the peristome of piensis and Periarchus altus. They reported three samples of M. tenuis did not differ sig slightly anteriorly eccentric peristomes for all nificantly gives confidence in the validity of the other species except the dendrasterids. ratios. The variation in the eccentricity ratios Beadle (1995) reported a strong correlation of the apical system in the three samples of M. between the location of the peristome and api tenuis suggests the control of the location of cal system in a sample of specimens pooled the apical system is less fixed. The location of from three species of Dendmster but did notre the apical system in D. excentricus (which is pos port whether the locations were correlated for terior) varies with habitat (Raup, 1956; Stanton individual species. In contrast, he found no etal., 1979). correlation between the location of the two in Beadle (1995) reported a range for the ec Echinamchnius parma. We found the eccentric centricity ratio of the peristome of E. parma of 0.95-1.05. The range for the eccentricity ratio ity ratio of the apical system and peristome are of the apical system was estimated from his similar only for M. tenuis. The two structures graph to be ca. 0.98-1.10. Beadle selected val are obviously uncoupled in development and ues nonrandomly to maximize variation, and function in general as Beadle (1995) conclud those given are the basis for his conclusion that ed for dendrasterids. neither the apical system nor the peristome of Cassiduloids are in the same clade as cly E. parma shows any pronounced tendency to peasteroids (Suter 1994a, 1994b; Smith et al. ward posterior displacement. Our statistical 1995), and it is instructive to consider them in analysis showed that the peristome of the pop this analysis. Kier (1972) made generalizations ulation of E. parma sampled is displaced pos regarding the position of the peristome of cas teriorly and that the apical system is decidedly siduloids although he did not quantify its po anterior. Hashimoto and Ujiie (1965) reported sition. For example, the peristome was usually both the peristome and apical system of Echi only slightly anterior in Jurassic cassiduloids namchnius microthyroides are very slightly ante and was actually central or posterior in the ge riorly eccentric. nus Clypeus. In Gentilia syriensis of the Creta Mooi and Harold (1994) reported the dis ceous, Kier reported a peristome located "very tance from the front ambitus to the madrepor eccentric anteriorly." In this genus, the ante ite of the neotype of M. quinquiesperfomta is rior ambulacrum III is very short or absent. 43.9%. This is equivalent to an eccentricity ra Mooi (1990) reported without comment inter tio of 1.14, similar to the mean found for the esting correlations between test shape and po population from Venezuela. However, the dis sition of the peristome in his key to the living tance from the front ambitus to the anterior cassiduloids. For example, despite showing di-

Published by The Aquila Digital Community, 1999 3 Gulf of Mexico Science, Vol. 17 [1999], No. 1, Art. 4 38 GULF OF MEXICO SCIENCE, 1999, VOL. 17(1)

rectional movement, the test margin of species bivalve Anadara (Pliocene), and the echinoid Den in the genus Conolampas is circular and the dmste~; Ph.D. diss., Indiana University, Blooming peristome is central or slightly posterior. In ton, IN. contrast, the test margin of species in the ge ALI, M. S. M. 1998. Some Miocene Scutellina (Ech nus Echinolampas is oval and the peristome is inoidea, Echinodermata), from the northern Western Desert, Egypt: a preliminary study, p. slightly anterior. Once again, we see no pro 541-546. In: Echinoderms: San Francisco, R. Mooi nounced change in body form or anterior po and M. Telford (eels.). Balkema, Rotterdam, The sition of the mouth in this group with direc Netherlands. tional movement. BATHER, F. A. 1900. The Echinodermata. Adam and The final question is why the peristome is Charles Black, London. not located anteriorly in a more pronounced BEADLE, S. C. 1995. Retrodisplacement of the oral way as predicted for species that show direc and anal openings in dendrasterid sand dollars. tional movement. Sand dollars do not move Evolution 49:1203-1214. rapidly (Parker, 1927; Weihe and Gray, 1968; BEKLEMISHEV, W. N. 1969. Principles of comparative Bell and Frey, 1969), and one hypothesis is that anatomy of invertebrates. Vol. 1: Promorphology. the speed of movement is not sufficient to re Univ. of Chicago Press, Chicago. BELL, B. M., AND R. W. FREY. 1969. Observations on sult in selection for an anterior location of the ecology and the feeding and burrowing mecha peristome. nisms of Mellita quinquiespe1jorata (Leske). J. Pa A second hypothesis concerns the mode of leontol. 43:533-560. feeding. Phelan (1977) suggested the greatly CLARK, W. B., AND M. W. TWITCHELL. 1915. The Me expanded ambulacral columns and adjacent sozoic and Cenozoic echinoderms of the United regions of the interambulacra that support ac States. Monographs of the United States Geologi cessory tube feet are homologous to the more cal Survey. Vol. 54. recognizable but less expansive phyllodes of COWEN, R. 1981. Crinoid arms and banana planta the cassiduloids. These tube feet accomplish tions: an economic harvesting analogy. Paleobiol food gathering and are associated with the ogy 7:332-343. food grooves on the oral surface of sand dol DAFNI,J. 1988. A biomechanical approach to the on togeny and phylogeny of echinoids, p. 175-188. lars (Ellers and Telford, 1984; Telford et al., In: Echinoderm phylogeny and evolutionary biol 1985; Telford and Mooi, 1996). Cowen (1981) ogy. C. R. C. Paul and A. B. Smith (eels.). Claren made an imaginative analogy between the pat don Press, Oxford. tern of arm branching in camerate crinoids DURHAM, J. W. 1949. Dendmster elsme~·ensis Durham, and the pattern of harvesting roads on banana n. sp. Am. J. Sci. 247:49-62. plantations. He showed the similarity of the ---. 1955. 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Occurrence and of the peristome in sand dollars that have the relative growth of Echinarachnius microthyroides Ni usual prone position would decrease efficient siyama from Soeushinai, Hokkaido. Bull. Nat!. Sci. feeding and thus be selected against. Mus. Tokyo 8:88-93. E.IER, P.M. 1972. Tertiary and Mesozoic echinoids of Saudi Arabia. Smithson. Contrib. Paleobiol. No, AcKNOWLEDGMENTS 10. We thank A. Debrot, M. Lesser, P. Penchasz Mom, R. 1990. Living cassiduloids (Echinodermata: adeh, and S. Stancyk for their assistance in ob Echinoidea): a key and annotated list. Proc. Bioi. Soc. Wash. 103:63-85. taining specimens and B. Wawrik for his assis ---. 1997. Sand dollars of the genus Dendraste~· tance in the laboratory. (Echinoidea: Clypeasteroida): Phylogenetic sys tematics, heterochrony, and distribution of extant LITERATURE CITED species. Bull. Mar. Sci. 6:343-375. ---.,AND A. S. HAROLD. 1994. Anatomical obser ALEXANDER, R. R. 1972. Autecological studies of the vations of the sand dollar Mel/ita quinquiespe1jorata brachiopod Rafinesquina (Upper Ordovician), the (Leske, 1778) (Echinodermata: Echinoidea) and https://aquila.usm.edu/goms/vol17/iss1/4 4 DOI: 10.18785/goms.1701.04 Lawrence and Pomory: Eccentricity of the Apical System and Peristome of Sand Dollars ( lAWRENCE AND POMORY-ECCENTRICITYOF SAND DOLlARS 39

the designation of a neotype. Proc. Bioi. Soc. echinoids: trying to see the phylogeny for the Wash. 107:741-759. trees. Bioi. J. Linn. Soc. 53:31-72. MoRTENSEN, T. 1948. A monograph of the Echinoi ---. 1994b. Cladistic analysis of the living cassi dea. IV.2. Clypeastroida. Clypeasterid::e, Arachno duloids (Echinodea), and the effects of character idid::e, Fibulariid::e, Laganid::e, and Scutelli::e. C. A. ordering and successive approximations weight Reitzel Publisher, Copenhagen, Denmark. ing. Zoo!. J. Linn. Soc. 112:363-387. NISIYAMA, S. 1966. The echinoid fauna from Japan TELFORD, M., AND R. Mom. 1996. Podia[ particle and adjacent regions. Part I. Paleontol. Soc. Japan picking in Cassidulus caribaearum (Echinodermata: Spec. Pap. 11. Echinoidea) and the phylogeny of sea urchin feed O'NEILL, P. 1978. Hydrodynamic analysis of feeding ing mechanisms. Bioi. Bull. 191:209-223. in sand dollars. Oecologia 34:157-174. ---,---,AND 0. ELLERS. 1985. A new model PARKER, G. H. 1927. Locomotion and righting move of podia! deposit feeding in the sand dollar, Mellita ments in echinoderms, especially in Echinarach quinqzdespe1jorata (Leske): the sieve hypothesis nius. Am. J. Psycho!. 39:167-180. challenged. Bioi. Bull. 169:431-448. PHELAN, T. F. 1977. Comments on the water vascular TIMKO, P. L. 1976. Sand dollars as suspension feed system, food grooves, and ancestry of the c!ypeas ers: a new description of feeding in Dendraster ex teroid echinoids. Bull. Mar. Sci. 27:400-422. centricus. Bioi. Bull. 151:247-259. RAUP, D. M. 1956. Dendrastm: a problem in echinoid WAINWRIGHT, S. A., W. D. BIGGS, J. D. CURREY, AND J. taxonomy. J. Paleontol. 30:685-694. M. GosLINE. 1976. Mechanical design in organ SMITH, A. 1984. Echinoid palaeobiology. George Al isms. Princeton Univ. Press, Princeton, NJ. len and Unwin, London. WEIHE, S. C., AND l. E. GRAY. 1968. Observations on SMITH, A. B., D. T. J. LITTLEWOOD, AND G. A. WRAY. the biology of the sand dollar Mellita quinquiespe1c 1995. Comparing patterns of evolution: larval and forata (Leske). J. Elisha Mitchell Sci. Soc. 84:315- adult life history stages and ribosomal RNA of 327. post-Palaeozoic echinoids. Phil. Trans. R. Soc. WoODRING, W. P., R. STEWART, AND R. W. RiCHARDS. Lond. B 349:11-18. 1940. Geology of the Kettleman Hills oil field, Cal STANTON, R. J., JR., J. R. DODD, AND R. R. ALEXANDER. ifornia. U.S. Geological Survey. Prof. Pap. 195. 1979. Eccentricity in the clypeasteroid echinoid Dendraster. environmental significance and appli UNIVERSITY OF SOUTH FLORIDA, DEPARTMENT OF cation in Pliocene paleoecology. Lethaia 12:75-78. BIOLOGY, TAMPA, FLORIDA 33620-5150. Date SUTER, S. J. 1994a. Cladistic analysis of cassiduloid accepted: December 17, 1998.

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