PHYLUM MOLLUSCA

Molluscs are bilaterally symmetrical, although some have secondarily lost the symmetry in part; they have well-developed excretory, digestive, respiratory and circulatory systems. In all molluscs except the cephalopods, the circulatory system is open. All molluscs are characterized by having three main body regions: a head-foot, which is the sensory and locomotor part of the body; a visceral mass, containing most of the organ systems; and a mantle, which covers the visceral mass and secretes the shell, if one is present. Most molluscs also have radula, a rasping structure covered with chitinous teeth, which is used in feeding.

"PHYLUM MOLLUSCA." Phylum Mollusca. Rutgers, n.d. Web. 16 June 2017.