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Modiolus areolatus (Gould, 1850)

Description: Shape equivalve, inequilateral, elongate, with umbo behind anterior end. Dorsal margin nearly straight; postero-dorsal end extended, broadly rounded. Hinge without teeth. Ligament long, narrow. Interior smooth, slightly nacreous, white, sometimes irregularly marked with purple, muscle scars not clearly defined. Exterior with irregular, concentric growth ridges. Periostracum brown, with hairs near the posterior margin when live.

Size: Up to 100 mm in length, usually less than 60 mm in NSW.

Distribution: New Zealand and Australia. In Australia, southern Qld, southwards and around southern Australia to south-western WA, including Tasmania.

Habitat: Lives intertidally and subtidally among rocks and seaweed, sometimes embedded in sponges.

Comparison: This is a large, broad shell with a brown exterior lacking any radial sculpture.

Synonymy: The current author has reverted to the view of Hedley (1923) in regarding this as a single species somewhat variable in shape over its wide distribution. Laseron (1956) divided it into two separate species. He named M. peronianus Laseron, 1956 (Fig. 1) from sand flats at Gunnamatta Bay, Port Hacking, and distinguished it by being half the size of the New Zealand M. areolatus “even narrower anteriorly and more elongate posteriorly”. He named his second species M. cottoni Laseron, 1956 (Fig. 2), with the type locality off Eden, NSW, in 30-50 fathoms (55-91 m). Compared to M. peronianus he described it as “a larger, frailer shell with a different contour, even narrower anteriorly.” Subsequent authors have used M. peronianus for NSW shells and M. cottoni for southern Australian shells. Modiolus cottoni Laseron, 1956 has previously been placed into synonymy by Lamprell & Healy (1998, sp. 166), but Modiolus peronianus Laseron, 1956 is here declared a NEW SYNONYM.

Remarks: Small beach-worn shells are often reddish in colour.

Fig. 1:  Paratype of Modiolus peronianus. Gunnamatta Bay, Port Hacking, NSW (C.089957)

Fig. 2:  Holotype of Modiolus cottoni. Off Twofold Bay, NSW, in 55 m. (C.090537)

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