Modern Forms



Some examples of modern bivalves include clams, scallops, oysters and mussels. A brief account of each of these forms is given here.

Picture from http://www.assateague.com/nt-bival.html

CLAMS

Clams are bivalves that use their muscle foot to dig down into the sand. To survive under the sediment they have long siphons that reach from the mantle to the surface of the sediment; their mode of life is deep infaunal. Clams are filter feeders; water and food particles are drawn in through the siphon to the gills where tiny hairs (cilia) catch the food. These food particles are then driven down along a groove to the palps, which push them into the clam's mouth. The second siphon then carries away the water. The gills are also used to extract oxygen from the water.

SCALLOPS

Scallops are epifaunal bivalves. They use their adductor muscle to rapidly open and close their valves, ejecting water around the hinge, an effective escape mechanism. Around the edge of the scallop's mantle is a series of blue eyes that are very weak but can detect the movement of nearby predators such as starfish. Scallops are hermaphroditic i.e. they have both male and female sex organs.

Picture from http://www.assateague.com/nt-bival.html

Picture from http://www.assateague.com/nt-bival.html

OYSTERS

Oysters either attach themselves to a hard substrate or they simply rest on the sea floor. They are generally non-mobile. Oysters filter-feed on micro-organisms that are brought into the shell via the current. They can change their sex during their lives, starting off as a male and usually ending as a female. The shape of oysters is very variable and mainly depends upon how many other oysters are crowded about them as they grow.

MUSSELS

Mussels may be marine or freshwater, with the latter forming mother-of-pearl inside their shells. Mussels attach themselves to hard substrates with the help of byssal threads from byssal glands. These sticky threads are so secure that mussels are able to live in very high-energy environments.


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