FRESHWATER CLAM-ASIATIC CLAM 



Corbicula fluminea , Muller 



The freshwater clam, or mussel, is quite extensive throughout 

 inland waters of the United States. Species range from a few 

 millimeters to over 100 millimeters in length. Many species have some 

 commercial value, while others are troublesome pests. 



The Asiatic clam, Corbicula fluminea, is a species that has caused 

 problems in irrigation systems in the Western United States by fouling 

 pumps and inlet screens, plugging tubes of heat exchange devices, and 

 reducing the carrying capacity of canals and conduits. These organisms 

 have been reported in numerous areas of California, Arizona, and the 

 Pacific Northwest; and some species of this genera are rapidly 

 spreading into freshwaters of the Eastern United States. 



Members of the Corbicula genus are easily recognized by the 

 distinctive concentric sculpture of the outer shell; but they are often 

 overlooked until the population becomes dense, because of their habit 

 of burying in the bottom mud. Some shells are thin and easily crushed 

 while others are very thick. The shells of these animals are divided in 

 halves or valves that are securely attached to each other by an elastic 

 hinge. Under natural conditions, the valves open slightly to allow 

 protrusions of the muscular foot at the lower margins of the shell. This 

 foot provides for sluggish locomotion of the animal. 



The animal feeds on microorganisms which are drawn into the 

 body cavity by an incurrent siphon. Wastes are excreted through a 

 similar or excurrent siphon. These siphons can be seen barely 

 protruding above the mud surface when the animal is feeding. During 

 periods of disturbances or unfavorable environmental conditions, the 

 animal will tightly close its shell halves and often bury itself deep into 

 the soil. 



The species is reproduced by development and hatch of fertilized 

 eggs within the adult clam. Individual clams may release thousands 

 of microscopic larvae, which soon take up residence on the bottom 

 strata. Little is known of the exact duration of the spawning season, 

 which occurs chiefly in the summer months with a number of 

 generations being produced in one season. 



A typical silt bar heavily infested with clams and remanent shells, 

 as might be seen in a canal, is illustrated. The shells of Asiatic clams 

 range from 35 to 50 millimeters in diameter when mature and vary 

 in shape from somewhat triangular to oval. 



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