SOME STUDIES ON THE GENUS LITHOPHAGA (MYTILIDAS, BIVALVIA) OF THE MALAY PENINSULA, WITH A REVIEW OF THE LOCAL MYTILIDAE

Abstract

Five species of the rock-boring mollusc, Lithophaga, (Mytilidae, Bivalvia) have been collected in the Malay Peninsula Region. One other species, although in record at the Singapore National Museum, was not found in recent collections, Keys to the subgenera and species of the local Lithophaga are constructed for easy identification. The mechanism of boring by Lithophaga is reviewed and discussed. Past and recent experiments strongly indicate that Lithophaga is probably a chemical borer although some mechanical aid cannot be entirely ruled out. Results of some histochemical studies on the mantle of Lithophaga showed that the tissues contained some kind of acid mucopolysaccharides. The kinds of substrates attacked by Lithophaga are briefly reviewed. Only calcareous materials have apparently been found with Lithophaga borings. The form and structure of the Lithophaga burrows and the types and species of corals bored by the date mussels are studied. The ciliary currents and feeding mechanisms in four Lithophaga species including the anatomy and histology of the ctenidia, are studied and found to be basically the same. The anatomy of Lithophaga is essentially similar to that of other mytilid species. The musculature of the local species of Botula, Lithophaga, Modiolus, Mytilus and Septifer is also basically similar, with, however, certain specific differences in the different genera, In particular, the anterior adductor muscle is found wanting in Mytilus viridis L., while a peculiar arrangement and form of the adductor muscles are soon in Septifer binocularis (L.). The food of Lithophaga consists mainly of both plant and animal plankton and other planktonic material like the eggs and larvae of other marine organisms. Only a qualitative study of the food of Lithophaga was made. Little or no detritus organic matter was found in the stomach contents of the date mussels. A review including a description and distribution of the various species of the Mytilidae found in the Malay Peninsula is given. Of the total of twenty-two mytilid species now recorded in this region, nine are new records, while a few species in the collection of the Singapore National Museum have not been found again recently. An account of the economic importance of the Mytilidae is given. The only mytilid species of any economic importance or that has any economic potential appears to be Mytilus viridis, the green mussel.