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Pinna muricata Linnaeus, 1758

Description: Shell moderately fragile. Shape sharply pointed anteriorly, rounded or straight posteriorly. Dorsal margin straight or weakly concave, ventral margin straight or weakly concave. Shell gaping at dorsal end and at byssal area at anterior-ventral margin. Hinge along anterior half of dorsal margin. Interior with nacreous layer occupying anterior half, divided into dorsal and ventral lobes by narrow, longitudinal groove; adductor muscle scar on dorsal half of nacreous area, sometimes extending onto ventral half. Exterior with 8-10 longitudinal ribs, with finer ribs between on large specimens, with open spines on larger ribs. Shell colourless to mid-brown.

Size: Up to 250 mm in length but usually much smaller.

Distribution: Indo-West Pacific, from east Africa to eastern Pacific Ocean; in eastern Australia, as far south as Norah Head (between Newcastle and Sydney).

Habitat: From the intertidal down to 60 m. Common in the tropics, uncommon in northern NSW, becoming rarer towards end of range.

Comparison: Pinna species are distinguished from Atrina species by the presence of a groove dividing the nacreous layer into halves. This species is smaller than P. menkei, has a fragile shell and, in good specimens, has spines on the ribs which are not present in P. menkei. Its adductor muscle scar is rounded in comparison to that of P. menkei, which is elongate.

Fig. 1: Brunswick Heads, NSW (C.430624)


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