: Like most mollusks, they have an open circulatory system where the heart pumps blood into the body cavity. Internal Anatomy Summary Characteristic Digestive
Mouth (near the foot), stomach, liver, and intestine. They lack a radula (grating tongue). Plate-like gills (ctenidia) located in the mantle cavity. Excretory Two kidneys that open into the mantle cavity. Nervous Simplified, consisting of three pairs of ganglia. Ecological and Economic Importance
: Swan mussels ( Anodonta ), thick-shelled river mussels ( Unio ), and giant clams ( Tridacna ).
: The body is laterally compressed and divided into two main parts: the trunk and the wedge-shaped foot . Unlike gastropods, bivalves lack a head, tentacles, and eyes.
