ClamsBivalvia

Bivalves are molluscs characterised by two hinged shell valves that fully enclose their soft body. These shells vary significantly in shape and surface texture, from smooth and rounded forms to heavily ribbed or spiny structures, often showing a wide range of colours and patterns. Sizes vary from shells a few millimetres wide to the giant clams (Tridacna spp.), which reach about 40 cm (16 in); the metre-long Tridacna gigas of the wider Indo-Pacific does not occur in this sea.

Most bivalves are sedentary, living buried in sand or rubble, cemented to hard substrates, or boring into rock or coral, but a few species are capable of movement, such as scallops that swim with quick clapping motions of their valves, or file shells that use tentacles for limited crawling. Most species are filter feeders, drawing water through siphons to strain out plankton and organic particles using their gills. Giant clams, however, also host symbiotic zooxanthellae in their exposed mantle tissue, supplementing their filter-feeding with photosynthesis. They are commonly found from the intertidal zone to depths exceeding 100 m (330 ft).