BRACHIOPODS 



83 



TABLE 5 



Shell Measurements of 

 ThecidelUna congregata in mm* 





Fig. 8 ThecidelUna congregata on corsil frond from same 

 place as Fig. 7. Specimen at broken edge has grooves on the 

 dorsal valve reflecting grooved surface to which ventral vfilve 

 is attached. Such dorsal reflection of ventral irregularities is 

 common in brachiopods. 



Fig. 9 ThecidelUna sp. in feeding position (specimen from 

 Curasao, photo courtesy D. L. Meyer, shown in Grant. 1972). 



(Fig. 5; and Grant, 1972: pi. 5, Fig. 21). This position 

 would be highly vulnerable to predators and damage by 

 grazing fish, possibly accounting for the preference toward 

 sheltered environments and development of a muscle sys- 

 tem with a quick closing mechanism (Rudwick, 1961; 

 Zumwalt, 1978). 



Thecidellina congregata occurs at 10 of the 18 locali- 

 ties where brachiopods were recovered, fewer than the 

 more widespread species F sanguinolenta. It is, however, 

 the most abundant species, being represented by at least 

 370 specimens (both dead and alive). Of this number, 340 

 were obtained from Biken Islet, on the seaward slope or 

 the seaward end of the channel leading out to that slope. 

 Its abundance increases with depth, to 65 m, but it is 

 doubtful that the abundance continues to increase to 

 depths as great as the 480 m reported by Cooper (1954). 



'Specimens cemented to substrate permit only length and 

 width measurements, but these afford an idea of size and varia- 

 tion. All measured specimens are from the underside of a thin 

 coral frond from locality 32022 (Biken, 28 m). 



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, 1914, Some Australian Brachiopods, R. Soc. Tasmania Pap. 



Ptoc.. 1913: 112 115. 



Cooper, G. A., 1954, Recent Brachiopods. Bikini and Nearby 

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, 1977, Brachiopods from the Caribbean Sea and Adjacent 



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, 1972, The Lophophore and Feeding Mechanism of the Pro- 



ductidlna (Brachiopoda), J. Paleontoi, 46: 213-248. 



, 1983, Argyrotheca arguta, a New Species of Brachlopod 



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