In contrast to roundworms, how do segmented worms elongate or stretch lengthwise?

The polychaetes

Cultured pearls are made by

Of all of the freshwater organisms, more freshwater clams are becoming endangered than other species. What is the likely reason?

Oligochaetes are primarily

The cocoon in the earthworm is produced by the

The radula

Cephalopods feed on

Gaseous exchange in gastropods may involve

Gas exchange in the earthworm occurs through the