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Family  Hemidonacidae

Hemidonax

Hemidonacidae is a numerically small family of moderate sized shells. It contains only the genus Hemidonax, which itself contains only six species. The family is restricted to the central Indo-West Pacific Ocean, with one species found in the Philippines-Indonesia region and the rest restricted to Australia. Only two species occur in NSW, these having a distribution from northern Queensland southwards to southern NSW. This is an unusual distribution which contrasts with the usual situation of Indo-West Pacific species which occur throughout the Indo-West Pacific and extend southwards into northern NSW.

The habitat of hemidonacids is not known with certainty, but they most likely burrow shallowly in clean sand in the shallow subtidal zone. They live sufficiently shallowly to be washed up on beaches, sometimes in quantity.

Family Reference

Ponder, W.F., Colman, P.H., Yonge, C.C. and Colman, M.H. 1981. The Taxonomic position of Hemidonax Mörch, 1871 with a review of the genus (Bivalvia: Cardiacea). Journal of the Malacological Society of Australia 5(1-2): 41-64.

Coverage

The only two species that occur in NSW are detailed here.

Identification Notes

The Hemidonacidae have shells similar to Cardiidae but with a triangularly elongate-oval shape.

Shell form Triangular elongate-ovate in shape; umbo well posterior to midline; external sculpture of radial ribs restricted to the posterior end.

Hinge: Two cardinal teeth in each valve; lateral teeth strong, one anterior and one posterior in the left valve, one or two anterior and posterior in the right valve (Fig. 1. Hinge of Hemidonax pictus).

Shell interior: Muscle scars subequal, pallial line continuous but without a pallial sinus.

Fig. 1: Hinge of Hemidonax pictus