diagram showing stages in development of a clam
Sexes are separate in most bivalves and paired gonads lie in the upper part of the foot region intermixed with elements of the digestive system. For this reason it is difficult to obtain reliable measuremens of gonad size; hence, gonad indices are unavailable. Paired gonoducts release gametes into the exhalent water flow just before it enters the exhalent siphon. Fertilisation leads to the development of a veliger larva that swims and feeds in the plankton for several weeks. This transforms into a bivalved form known as a pediveliger, that is the settling stage. All developmental times shown in the schematic are, of course, temperature-dependent. Abraham & Dillon 1986 Life histories & environmental requirements of coastal fishes & invertebrates. Biol Rept 82 SOFTSHELL CLAM U.S. Wildlife Serv, Natl Wetlands Res Center, Lafayette, LA.
NOTE about 4% of bivalves are hermaphroditic
NOTE a measure of size of gonad relative to body mass, changes in which allow seasonal cycles of gonadal growth and spawning to be monitored