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Bivalves
Find out what species of spectacular marine snails, nudibranchs, land and freshwater snails inhabit the reefs, rocky shores, forests, and suburban gardens of Queensland.
Overview
Bivalves are molluscs that have a shell composed of two valves attached by a skin-like ligament and usually interlocking hinge-teeth. The class Bivalvia includes many commercially significant species and numerous ecologically dominant groups. Although they are predominantly marine, there are also a number of families of freshwater mussels. The marine families consist of many groups that have been important to humans globally for thousands of years – either for food or cultural uses such as jewellery or decorative inlays. Examples include the various species of oysters, mussels, cockles, pearl oysters, arks, pipis, razor clams and scallops.
Many bivalves live in the sediments (venus clams and trough shells) and others live on the surface (mussels and oysters). The mantle, lining the inside of the shell, essentially encloses the animal. The head is poorly developed, and a radula (tongue ribbon) is absent. In most, the gills perform both breathing and food-gathering roles (filter-feeding). The foot is well-developed in burrowers (such as pipis), but poorly developed in attached forms like oysters and swimmers such as scallops. About 350 species have been recorded from Moreton Bay in south-east Queensland.
Common questions
The Giant Clam, Tridacna gigas, is the largest bivalve. It can reach 1.2 meters across and weigh more than 200 kilograms. There are other species of ‘giant clam’ in the genus Tridacna, but none reach such extraordinary dimensions.
There are many species of oysters, mussels, scallops, cockles and clams that are harvested and cultivated throughout the world. Edible species occurring in Queensland include the Sydney Rock Oyster, Saccostrea glomerata, and Ballot’s Saucer Scallop, Ylistrum balloti.
The majority of bivalves draw in water containing plankton (mostly), detritus and bacteria using an inhalant siphon. The gills then direct this food to flap-like lip-extensions and then to the mouth. The filtered water is later expelled using an exhalant siphon.
Only some of them, most can’t. Many bivalves (e.g., cockles and arks) live either just below, or deeply buried beneath, the surface of sand or mud substrates; others (e.g., oysters and mussels) are attached to rocks or rubble. However, some species such as the Fragile File Clam, Limaria fragilis, and Ballot’s Saucer Scallop Ylistrum balloti, can swim by expulsion of water when rapidly opening and closing their shell valves.
Fact sheets
Mud Ark
One of the most abundant bivalve molluscs on the mud and sand-flats of eastern and southern Australia, the Mud Ark can reach a shell length of almost 70 mm.
Strawberry Cockle
The Strawberry Cockle belongs to a group of molluscs known as bivalves (two shells). It is creamy white with strawberry-red scales and has a solid, strongly ribbed shell with a marked ridge along one side.
Sydney Rock Oyster
The Sydney Rock Oyster (Commercial Oyster) is the most ecologically and commercially important species of the oyster family (Ostreidae) from Australian waters.
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