BRACHIOPODS 



81 



TABLE 3 



Measurements of A. arguta 

 in mm from Ikurin (sta. 32014)* 



'Most specimens are preserved 

 still attached to their substrates, so 

 the thickness measurement was 

 impossible to obtain. 



tHolotype: USNM 265875 



only at two localities, both in association with Thecidellina 

 congregata. One locality is on the seaward side of the reef 

 and the other on the lagoon side; both are on the 

 southwest segment of the atoll [Biken and Ikurin where 13 

 and 19 specimens were found, respectively (Table 2)]. 



The shell of Frenulina sanguinolenta is small for bra- 

 chiopods in general and even for a species of Frenulina. 

 yet this is the largest brachiopod at Enewetak. Adults nor- 

 mally are slightly wider than long, and the shape is that of 

 a generalized terebratulide, with biconvex profile and api- 

 cal circular foramen (Figs. 4 and 5) that earned the bra- 



Fig. 4 Frenulina sanguinolenta from pinnacle in lagoon, 

 locality 32010; the largest specimen collected (w is 12.3 mm) 

 and a smaller one (w is 6.9) with pedicle and loose pedicular 

 fibers (2 X). 



>4 



" "J* ' ."a^^^B 



'■^.''^' 



Fig. 5 Frenulina sanguinolenta from niches at 24 m depth in 

 the lagoon, shown attached to substrate (4X). Shells are pink 

 with white stripes or solid pink. 



chiopod the vernacular name "lamp shell" (the ancient oil 

 lamp). The color is distinctive, normally white with pink 

 stripes or pink mottling in irregular rows but occasionally a 

 solid pink or red color without stripes. The dorsal valve 

 bears a shallow median depression resulting in a sulcate 

 anterior commissure. 



The dorsal loop consists of a large "hood" of thin shell 

 material attached to a short slim median septum by means 

 of two broad lateral bands. The ventral valve has deltidial 

 plates outlining the anterior part of the foramen, which are 

 conjunct in some specimens but disjunct in most. The 

 species thus is variable, but unmistakable, in the Enewetak 

 brachiopod fauna. 



Frenulina sanguinolenta is the most widespread and 

 smallest living species of the genus (Hatai, 1940; Cooper, 

 1957). This species like other brachiopods at Enewetak 

 prefers cryptic habitats. It is not as abundant locally as T. 

 congregata but was found at more localities than any 

 other brachiopod species, being present at 14 of the 18 

 localities sampled ( Table 2 ). Most sf)ecimcns remain 

 attached to their substrates by the pedide, so only the 

 width measurement could be made without danger of dam- 

 age to the shells. Table 4 compares the length, width, and 

 thickness of 14 Enewetak specimens. However, the smal- 

 lest specimen examined had a width of 0.8 mm. The beak 

 curves toward the substrate, so the dorsal valve is held 

 facing the coral frond or other "overhang" that the shells 

 cling to. Relative to the sea floor, the dorsal is thus upper 



