THE IDENTIFICATION OF THE MYTILIDS MUSCULUS VIRGILIAE BARNARD, ARCUATULA CAPENSIS (KRAUSS) AND BRACHIDONTES VARIABILIS KRAUSS, WITH CORRECTIONS TO THE LITERATURE AND A NOTE ON THEIR DISTRIBUTION

Summary

The identification of Musculus virgiliae Barnard has been frequently confused with both Arcuatula capensis (Krauss) and Brachidontes variabilis Krauss. B. variabilis can be separated from M. virgiliae on the grounds of habitat and external morphology. The separation of A. capensis from M. virgiliae is more difficult. due to similarities in habitat preference. M. virgiliae is found at the heads of estuaries, while A. capensis is associated with muddy substrata, close to estuary mouths. There is a considerable overlap zone in the Kowie estuary and this kind of distribution may account for some past misidentifications.

The characters most useful in separation of the three species are:

B. variabilis, terminal umbones, no prominent denticles on anterior internal valve margins. weak antero-posterior external riblets;

A. capensis, strongly subterminal umbones. no denticles on anterior internal valve margins, no antero-posterior external riblets, pronounced dorsal sweep of the anterior margins of both valves;

M. virgiliae. subterminal umbones, pronounced denticles on anterior internal valve margins, pronounced antero-posterior external riblets.