Zoology 10th Edition by Stephen Miller,John Harley

Exercise 14

The class Bivalvia is the second largest of the molluscan classes. Bivalves are enclosed in a shell consisting of two valves. Most bivalves are filter feeders, using their mantle cavity and gills to filter food materials. Reproduction usually involves the formation of free-swimming larval stages. Bivalves live in nearly all aquatic habitats. They live completely or partially buried, attached to solid substrates, or inhabiting chambers that they bore into submerged wood, coral, or limestone.
What anatomical feature typical of most molluscs and bivalve ancestors is absent in modern bivalves, and what accounts for its loss in members of this class?
FIGURE 11.13 Larval Stages of Bivalves. ( a ) Trochophore larva (0.4 mm) of Yoldia limatula. ( b ) Veliger (0.5 mm) of an oyster. ( c ) Glochidia (1.0 mm) of a freshwater clam. Note the two tooth-like hooks on upper glochidium used to attach to fish gills.
FIGURE 11.14 Class Bivalvia. This photograph shows a modification of the mantle of a freshwater bivalve ( Lampsilis reeviana ) into a lure. The edge of the bivalve shell is shown in the lower right corner of the photograph. When a fish approaches and bites at the lure, glochidia are released onto the fish.