There are 50,000 known species of Mollusks. Some of the most well-known would include: snails, octopuses, squid, clams, and scallops. In general, mollusks have 3 body regions: a head, a visceral mass, and a "foot." The head contains the sense organs and the mollusk's "brain," while the visceral mass contains the internal organs. The "foot" of the mollusk is the muscular lower part of the body. Mollusks usually have a shell even though there are many that do not. Mollusks also have an extension of the body wall called the mantle. This portion of the animal's anatomy is responsible for secreting the shell. The mantle encloses the mantle cavity which contains the gills, anus, and excretory pores.
The digestive system of mollusks
Mollusks break up their food using a radula which is a tongue-like structure with hooks called cuticulae which act as teeth. After the snail attains its food, the food is then transported to the digestive tract.The digestive tract starts at the head with the mouth, continues down to the esophagus, the crop, then to the stomach, to the intestines, and ends at the anus. The anus is located in the front of the mantle cavity, where all the undigested waste is released.
The garden snail’s digestive system begins with its buccal mass, which is basically the mouth. It is used to intake the food that is being digested. After going through the snail's mouth, it passes through the radula, where the food is broke up and cut into pieces that can be digested more easily. The oesophagus, which is connected to the snail's stomach, is used to transport the broken down food from the radula to the stomach.
The squid's stomach has very rough walls that are used to break down the food. This "breaking down" gets all of the digested foods nutrients. The squid's esophagus is covered with mucus, so the food will withhold in the esophagus until it is fully broken down and the radula grinds it up. Lastly, the food is transported into the stomach of the squid.
Most scallops are filter feeders. The plankton sometimes has scallop larvae in it. Siphons bring water over a filtering structure. Mucus then traps the food. Next, the cilia on the structure moves the food to the mouth. Then, the scallop digests the food in the stomach and digestive gland.