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7762-1.jpg (504215 bytes)



Cosa parallelogramma (Hedley, 1906)

Description: Shell minute. Prodissoconch a semicircular disc. Shape subovate, extended posteriorly. Anterior end straight or concave, posterior end and ventral margin smoothly rounded. Umbones at anterior end of hinge. Hinge line straight, with about 30 microscopic teeth on posterior side, 8 on anterior side, separated by wide, low triangular ligament pit. Interior white, ribbed by external sculpture, margin strongly crenulate. Exterior with about 17 very strong radial ribs and concentric riblets visible as fine threads in the interspaces and sometimes scales at intersections. Periostracum Not seen. Shell colour white.

Size: Up to 3 mm in length.

Distribution: Known from Moreton Bay, Qld, southwards to Montague Island (near Narooma) NSW.

Habitat: Known from beach washup, and dredge samples down to 150 m.

Comparison: This species stands out among the NSW species because of the strong sculpture.

Fig. 1: 7762-1 Off Long Reef, Collaroy, NSW, in 26 m (C.364302)


Copyright Des Beechey 2023