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Cosa pharetra Iredale, 1931

Description: Shell minute. Prodissoconch a semicircular disc. Shape subovate, extended posteriorly. Anterior and posterior ends smoothly rounded. Umbones at anterior third of hinge. Hinge line straight, with microscopic teeth, about 30 posteriorly, 15 anteriorly, separated by ligament pit. Interior white; margin denticulate with about 5 denticles posteriorly, many ventrally in mature shells. Exterior with fairly weak, dense radial ribs stronger centrally and dense concentric ridges. Periostracum not seen. Shell colour white.

Size: Up to 2.2 mm in length.

Distribution: Cape Moreton, Qld, southwards to eastern Vic and Tas.

Habitat: Subtidal, 80-400 m. Common.

Comparison: The umbones are at one-third of the hinge from the anterior end, immediately separating this from C. pectinata. In shape, it is similar to C. tatei but the sculpture is fairly weak but dense.

Fig. 1: Off Cape Naturaliste, N.E. Tasmania, in 399 m (C186282)


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