Freshwater mussels

Code KP019999

Class Bivalvia: Order Eulamellibranchia. Formerly known as Mutelidae when revised by McMichael and Hiscock (1958).

Elongate bivalved molluscs, somewhat similar in shape to sea and brackish-water mussels of family Mytilidae, but restricted to freshwater.

Hyriidae are bottom-dwelling, filter feeding bivalves. They occur in still or running water and often are found in seasonally shallow lakes and rivers with a firm, silty mud bottom. Dry periods generally are survived by forming a cocoon in the mud. The family is restricted to South America and Australasia with 6 genera and 17 species recorded from Australia. They range throughout mainland Australia and in Tasmania only in the South Esk River system of north Tasmania. Some species are endemic to particular catchments whilst others are cosmopolitan.

The ecology of some species has been studied by Walker (1981), with additional in formation from Smith (1996). Fertilisation takes place in the gill chamber, giving rise to larvae, called glochidia , which are parasitic on the fins, gills or general body surface of freshwater fish. Here they encyst and become covered by fish tissue. The parasitic stage may last from days to months, after which the mussel drops off and settles as a young adult. Young mussels are rarely collected.

External shell morphology can be greatly affected by environmental factors and this makes generic and species level identification difficult. In fast flowing waters, individuals tend to develop elongate shells whereas on gravel substrates the shells generally are heavy. Fluctuation in the physical, chemical or biological environment tends to cause shell dulling or deformity. The internal morphology also alters with shell form: eg. the adductor muscles are larger in bigger shells. Erosion of shells with age produces further morphological diversity. Bivalves accumulate toxic chemicals in the tissues, and hydriids, notably genus Velesunio , have been used to monitor organochlorine pesticide levels.

References:

McMichael, D.F. and Hiscock, I.D. (1958). A monograph of the freshwater mussels (Mollusca: Pelecypoda) of the Australian Region. Australian Journal of Marine and Freshwater Research 9 : 372-508.

Smith, B.J. (1996) Identification keys to the Families and Genera of Bivalve and Gastropod Molluscs found in Australian Inland Waters . Cooperative Research Centre for Freshwater Ecology Identification Guide No. 6., Albury, NSW.

Walker, K.F. (1981) Ecology of freshwater mussels in the River Murray. Australian Water Resources Council Technical Paper 63 : 1-119.