Feeding, Digestion, and Extraction

Mollusca of the Bivalvia class are filter feeders. The most well known of these species is the clam. When a clam opens and closes its shell, it sucks water through the incurrent siphon, into its body, creating a current. This current travels through the gills of the clam. Many glands excrete mucous which coats the gills. while the clam respirates, tiny bits of food are caught in the mucus. This food filled mucous is then pushed along by cillia on the gills of the clam to the mouth where it is digested. After the food is digested, it is shot out of the excurrent siphon. The liquid waste is removed by the extractory gland and shot out of the siphon as well. This way of trapping food in mucous is quite similar to the way dirt particles are caught in the mucus of a human's nose, and then brought into the stomach for digestion.

Many molluscs feed using their radula. The radula is a chitin enforced tongue that is used to scrape algae, plant or animal matter off of the surface that the specimen is grazing over.

Cephalopods also feed using a radula but they also have a hard beak used to break open the shells of clams and crabs. Using their long tentacles they quickly snag their prey before pushing it towards their mouth. The beak then breaks open the shell and many digestive enzymes are excreted from glands around the mouth to digest the prey. The liquids are then sucked into the mouth, and the shell is dropped.