|
 Bivalvia
The class bivalvia consists of clams, oysters, scallops and
mussels. They are defined by the presence of two
laterally-compressed shells, hinged together by an elastic ligament
and shell teeth. The shells are closed by well-developed
adductor muscles.
Bivalves have a siphon that moves water, waste, food and
gamets. They have gills for respiration but lack a radula.
Mytilus californianus
The bivalvies are filter feeders, using currents set up by
cilia on their gills to bring in food particles. Particles are
trapped in mucus secreted by the gills and labial palps, and
moved to the mouth by ciliary action.
A few bivalves, such as scallops, are able to move rapidly
by clapping their valves together. Others are able to move slowly
by muscular action of their foot. Some are burrowers in sand,
wood and rock while others, like mussels, are sessile attached
permanently by secreted byssal threads.
|