Parapholas quadrizonata (Spengler, 1792), dominating dead-coral boring bivalve from the Maldives, Indian Ocean

Endolithic bivalves were studied to establish abundance ranking and bioerosive impact on Maldivian coral reefs. In samples of dead coral, Parapholas quadrizonata (Spengler, 1792) was by far the most numerous bivalve borer. The assemblages of variously sized and aged specimens, their spatial situation and the resulting behaviour are described and discussed. The morphology of shells and boreholes is illustrated. Intra-species competition for space may have restricted the individual growth but was not necessarily lethal. The borings show unique internal features that allow distinction from those of Gastrochaena species, whereas the borehole apertures are undistinguishable between the two genera.