< Previous species


Next species >

7774-1.jpg (505740 bytes)



Cosa stephensensis Laseron, 1953

Description: Shell minute. Prodissoconch a flat or concave semicircular disc. Shape subovate, extended posteriorly. Anterior end straight or concave dorsally, rounded ventrally; posterior end smoothly rounded. Umbones at anterior end of hinge. Hinge line straight, with microscopic denticles, separated into two groups by ligament pit. Interior white, margin weakly crenulated and with 5 strong denticles posteriorly. Exterior with about 12 narrow radial ribs and weaker concentric ribs. Periostracum not seen. Shell colour white.

Size: Up to 3 mm in length.

Distribution: The type specimens are from beach washup in Port Stephens. Specimens that are probably this species are known from beach washup in Sydney Harbour, Gerringong, and Batemans Bay.

Habitat: Known from beach washup.

Comparison: This species is similar to Cosa pectinata but has a greater umbo to ventral margin ratio. The number of radial ribs (about 12) is the same as that seen in sparsely ribbed specimens of C. pectinata, but C. pectinata is a deep water species, known from 50-183 m depth, while C. stephensensis is known, so far, only from beach washup.

Fig. 1: SYNTYPES Port Stephens, NSW in shell sand (C.090219)


Copyright Des Beechey 2023