The phylum Mollusca is composed of snails and slugs (gastropods), squid, cuttlefish, and octopi (cephalopods) and clams. Mollusks are soft-bodied animals which usually have an internal or external shell and complex organ systems. The digestive system of a mollusk begins with its mouth. Its radulae which contains small teeth and serves as a tongue, scrapes algae and bacteria from rocks. Also in the mouth, are digestive glands that secrete mucus and trap food. Moving cilia then drive the mucus towards its stomach. The ingested food particles are sorted by cilia and large particles are digested in the stomach and smaller particles are excreted through the prostyle from which waste and mucus are excreted. Cephalopods obtain food by capturing prey with tentacles, bringing the prey to their mouths and using their beaks to bite it. The digestive system of a cephalopod contains four parts. Food passes through the crop, then to the stomach, to caecum, and then to the intestine. Digestion takes place in its digestive glands, and nutrients and wastes are exchanged stomach and digestive gland.
Dosidicus gigas (Humboldt Squid) The Humboldt squid, obtains its food by preying on ocean life such as fish, crabs, shrimp, and even other squid. The Humboldt squid uses its tentacles to catch its prey and then brings it to its beak where the prey is killed and shredded. Like all cephalopods, the Humboldt squid has a complex digestive system. Once food enters through the beak, it goes to the crop where it begins to be broken down. From the crop, the food goes to the muscular stomach where it is stored until it moves to the caecum where digestive enzymes are released to facilitate the breaking down of food. Next, food goes to the digestive gland or liver where nutrients are absorbed. Then, solid wastes are excreted through the anus.
Arion vulgaris (Spanish slug) The Spanish slug obtains its food by using its radula to scrape bacteria and algae from rocks and cutting small vegetation. The digestive system of the Spanish slug consists of the pharynx, esophagus, stomach, digestive glands, intestine, and anus. When food enters the slug by its radula, as a strain of mucus and food, it goes to its pharynx and then esophagus. From the esophagus, it enters the stomach. The stomach of the Spanish slug is lined with cilia which separates the mucus from food. Digestive glands in the stomach release enzymes that break down the ingested food. The cilia also separates large food particles from small ones and the large food particles enter the digestive gland where nutrients are absorbed. The small food particles enter the intestine where it is formed into solid waste. The solid wastes exits through the anus.
Cerastoderma edule (Cockle) The common cockle obtains its food by filter feeding or using its gills to capture food particles that contain phytoplankton from the surrounding water. The digestive tract of a cockle consists of an esophagus, stomach, and intestine. Cockle's digest both intracellularly and extracellularly in their digestive tracts. Once food enters the cockle's esophagus, it moves to the stomach where digestive glands release digestive enzymes to digest the food extracellularly. The stomach also contains cells that eat small particles or phagocytes and digest them intracellularly, diffusing nutrients to other cells. From the stomach, food travels to the intestine where nutrients are absorbed and wastes are consolidated. The solid wastes are expelled through an anal pore.