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The clam is a flat, round invertebrate that posses a shell which consists of two separate valves. The two valves are held together by a hinge and the shell is kept closed by a tense abductor muscle.  Each valves is created by secretions from the mantle and each valve consist of three layers (Porch, p468). The first, outermost layer is meant for protection and it has a rough, bumpy texture. The middle layer is a hard, protective layer made of calcium carbonate. Lastly, the third innermost layer is made of a smooth, pearly substance. Because it is a mollusk, the clam has a foot which it uses to burrow in the sand. The clam has two tube-like siphons that it uses to filter water. Water is brought into its body through the incurrent siphon and the water is removed from its body through the excurrent siphon. The clam breathes using it's gills. Water containing oxygen is brought into the gills and the many blood vessels within the thin-walled gills exchange carbon dioxide. The gills also assist in obtaining food. The incurrent siphon brings water into the gills and mucus secreted by the gills and the palps, which are organs surrounding the clams mouth, capture tiny bits of food . The food is then moved by cilia on the palps through the esophagus and into the stomach. The food particles are later digested by the digestive gland attached to the stomach. The intestines take care of indigestible materials and expel them trough the anus. A clam has an open circulatory system with a pumping heart that send its clear blood through the blood vessels to distribute food an oxygen. A clam also has one kidney to filter the waste from its blood. Within the clam’s nervous system are three ganglia which are connected by nerves and sensory organs including light and touch receptors on the mantles edge.
Clams reproduce sexually and like most mollusks they are hermaphroditic, although some soft shelled clams are dioecious, meaning they have distinct genders. Some clams begin as males and as they grow older turn into females . Clams mate in the spring when the water temperature begins to rise. The clams release both their sperm and their eggs into the water to be fertilized. Once a free swimming sperm fertilizes the cells within the egg divide until they form a free swimming, larval called a trochophore (Porch, p469). The trochophore shows no resemblance to its parents for they lack a shell and are more round than flat. The trochophore matures into a veliger, which is the second stage of its development. The veliger begins to resemble its parents with the beginning stages of a shell. The veliger has a unique way of feeding. A formation of cilia surrounding the mouth called a velum assist the veliger capture food particles. The velum is also used to push the veliger through the water (Russell, p5). The third and final larval stage is called the pediveliger. The pediveligar has a ciliated foot and it is no longer a swimming larva. The pediveligar burrows into the sediment where it develops into a mature clam.
From oceans to rivers to ponds, clams can be found in almost any squatic anvirement. There over 15,000 species of clams worldwide. Both freshwater and marine clams spend their lives burrowing freely through the sediment near the shore. Allmost all clams are motile and can move about freely through the sand, allthough there are a few exceptions such as the Giant Clam, which is sessile and spends the majority of its life fastened to one spot . Clams are filter feeders, meaninf they feed on pankton strained from the water using their siphon. Clams can very in sizes but are typically small in caomparision to other animals.
- BIOLOGY Third Edition, Thomas E. Porch and Brad R. Bratorf, BJU PRESS, 2005 .
- The Illustrated Manual of Hard Clam Reproduction and Development Carrie J. Deming, Jeffrey C. Gruber, Norman R. Dollahon, Russell Williams, George E. Flimflin Jr., Jerry Zodl, and Micheal P. Russell, New Jersey Sea Grant, 1998.
- reference title author, publisher, date.