Crassadoma

Adults of Crassadoma gigantea have one valve (the right valve) fixed to a base, often a vertical rock face. This valve often becomes deformed to fit the contours of the rock. The left valve is roughly circular but irregular in outline, thick and heavy, with deep radial ribs. Every third or fourth rib is clad with blunt spines that overhang each other. These often get abraded and worn smooth as the scallop ages. There are flaps of shell known as auricles on either side of the straight hinge. The general colour is brown with the inside of the shell being glossy white with a purple patch at the hinge and a large, central adductor muscle scar. Crassadoma gigantea grows to a diameter of in the intertidal zone and in the subtidal zone. Between the valves, the margin of the orange mantle can be seen, with a row of tiny blue eyes and a sparse fringe of short tentacles. ==Distribution and habitat==

Crassadoma gigantea is found on the Pacific Coast of North America, from British Columbia south to Baja California and Mexico. ==Biology==

Like other scallops, Crassadoma gigantea is a filter feeder, filtering phytoplankton from water as it passes over the gills. The particles are moved by cilia along grooves to the mouth where edible matter is separated from sediment particles. The waste is incorporated into mucous balls which are removed from the mantle cavity periodically by a clapping of the valves. Crassadoma gigantea is cryptic and difficult to detect because of the sponges, sea anemones, hydroids, barnacles, bryozoans, worms and algae which tend to grow on the shell. The parasitic boring sponge Cliona celata damages the shell by making hollows in it. Additional shell material is laid down by the mantle tissue to compensate for this. Other sponges, such as the yellow boring sponge (Cliona californiana) that grow on the shell may be considered mutualistic, granting some protection against predators such as the sunflower starfish (Pycnopodia helianthoides) and purple sea star (Pisaster ochraceus). ==References==