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Family  Dimyidae

Dimyarian Oysters

The Dimyidae is a numerically small family, containing only about 15 species (Huber, 2010) of oyster-like bivalves. They live with the right valve attached to the substrate, which may be rock, coral, shells or a shell fragment. The growing dimyid may soon exceed the size of the attached object, with most specimens only showing a small proportion of the right valve attached.

The family is distributed worldwide, mainly tropical, and well represented in the Pacific. Dimyids are known from the subtidal down to bathyal depths; Huber (2010) reported specimens of the family living down to 1250 m. In NSW dimyids are common at moderate depths, from 50-530 m.

There is only one species recorded from NSW. Its distribution, and that of dimyid species in general, is poorly known, so it is not known if this species is restricted to NSW, or to Australia, or if it is a component of a more widely distributed species. Superficially, it appears similar to Dimya japonica from Japan.

Dimyids are so named because they have two adductor muscles, unlike other oysters which have only a single one. The anterior muscle is small compared to the posterior muscle which is composed of separate sections of smooth and striated muscle, producing a shell scar of two overlapping circles (not obvious in the photographs here, but illustrated in The Southern Synthesis).

Family Reference

There is no comprehensive reference to the family.

Coverage

The only species in NSW is documented here.

Identification Notes

In this family, identification relies on the characters of the species. The muscle scars are distinctive for the family, but often are not clearly shown in individual shells.