Brachiopods of Eneivetak Atoll 



Chapter 9 



RICHARD E. GRANT 



Department of Paleobiology 

 National Museum of Natural History/ 

 Smithsonian Institution, Washington. D. C. 



20560 



Brachiopods have one of the longest continuous his- 

 tories of any extant group of metazoans, originating in the 

 early Cambrian period and still thriving in modern seas. 

 Although brachiopods have long been considered rare and 

 in evolutionary decline, modern studies show they are 

 abundant, widespread, and highly diverse. Living bra- 

 chiopods are classified into about 100 genera and occupy 

 niches from tide pools to the abyss; their apparent rarity is 

 partly the result of their patchy distribution. Those on 

 Enewetak are small and inconspicuous, living in "cryptic" 

 habitats under the shade of coral fronds, in recesses in the 

 reef, or on lagoon pinnacles. Hitherto, the only published 

 account of them at Enewetak is as fossils from drill holes 

 (Cooper, 1964), although their presence alive on the reef 

 is well-known (Grant, 1971; Zumwalt, 1978). 



Three species, Thecidellina congregata Cooper, 

 Frenulina sanguinolenta Gmclin, and Argi/rotheca argute 

 Grant, are known at Enewetak from shells. In addition, 

 Lingula sp. is known by larvae taken in plankton tows in 

 the lagoon (Gilmartin, 1958), and a species of Crania is 

 expected based on specimens found at Bikini (Cooper, 

 1954). These taxa seem to constitute a suite of bra- 

 chiopods that characterizes the shallow waters of tropical 

 islands, not only in the Pacific (Cooper, 1954) but also in 

 the Caribbean and, with some different species, in the Red 

 Sea (Jackson et al., 1971). (See Table 1 for checklist of 

 Enewetak species and Fig. 1 for map of Enewetak.) 



METHODS 



Brachiopods were collected during September 1969 by 

 the author using scuba equipment to depths of about 50 

 m. Further collections of Thecidellina congregata to a depth 

 of about 65 m were made in 1972 by G. S. Zumwalt. His 

 specimens are deposited in the United States National 

 Museum of Natural History (USNM) and were used to sup- 



TABLE 1 

 Checklist of Enewetak Brachiopods 



Class INARTICULATA 

 Order LINGULIDA 



Superfamily LINGULACEA 

 Family LINGULIDAE 



Lingula sp., larvae: Gilmartin, 1958. 

 Class ARTICULATA 



Order TEREBRATILIDA 



Superfamily TEREBRATELLACEA 

 Family MEGATHYRIDIDAE 



Argyrotheca arguta Grant: Grant, 1983. 

 ( = Argyrotheca sp. Ccx)per, 1954.) 

 Family DALLINIDAE 



'Frenulina sanguinolenta Gmelin, 1792. 

 Order THECIDEIDA 



Superiamily THECIDEACEA 

 Family THECIDELLINIDAE 



Thecidellina congregata Cooper, 1954. 



{= Thecidellina maxilla Hedley: Grant, 1972.) 



'New Enewetak record. 



plement material for this report. Each station where bra- 

 chiopods were obtained has been assigned a number in the 

 USNM register of localities. Department of Paleobiology. 

 Station data are summarized in Table 2. The Enewetak 

 brachiopods cannot be seen under water because they are 

 small and live in dark habitats; therefore, collecting had to 

 be somewhat random. Pieces of coral were broken out of 

 likely looking habitats and brought to the surface for exam- 

 ination, much in the manner described by Jackson et al. 

 (1971) although not on so vast a scale. Most individuals 

 were left attached to their coral slabs and were dried in 

 the sun; those that became detached were preserved in 

 alcohol for immediate study and were dried later. 



ECOLOGY 



Brachiopods were found on Enewetak at depths rang- 

 ing from 5 m to 65 m, the limit of scuba equipment. At 

 Bikini, where they were collected by dredging, they are 

 reported as deep as 480 m (Cooper, 1954). The shal- 

 lowest occurrence was a small Frenulina sanguinolenta on a 



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