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Plicatula plicata (Linnaeus, 1764)

Description: Shell thick. Shape subcircular, elongate or trigonal. Right valve adherent to substrate and shaped by it; either all or part of valve adhered, commonly umbonal region only. Left valve weakly or substantially domed. Hinge line short. Hinge with 2, strong, V-shaped teeth. Interior white, with single pronounced muscle scar almost centrally. Exterior with strong radial ribs which are scaley, irregular, bifurcating towards margin on large shells. Shell colour white or reddish brown, sometimes with red flecks on radial ribs.

Size: Up to 50 mm in height.

Distribution: In Australia, known from NT, Qld and NSW, as far south as Sydney; specimens have been found alive at Long Reef, Collaroy, but Sydney Harbour dredged specimens are probably fossils representing a vagrant population that lived there during a time of warmer sea temperatures. Some authors (e.g., Okutani 2000) regard this species as having an Indo-West Pacific distribution, which includes northern Australia.

Habitat: Lives attached to rocks, corals or shell debris from intertidal down to 200 m depth.

Comparison: A similar species from northern Australia is Plicatula australis Lamarck, 1819 which has more numerous and finer ribs.

Synonymy: According to WORMS, synonyms include Plicatula chinensis Mörch, 1853, Plicatula essingtonensis G.B.Sowerby II, 1973 and Plicatula essingtonensis elusa Iredale, 1931. The latter name was assigned to a specimen from Sydney Harbour, not because the shell was different morphologically to that from Port Essington in the NT, but because it came from a different place.

Fig. 1: Off Tweed Heads, NSW, at 5 m depth (C.74125)


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