Mollusca Digestive System
The most common similarity among the various Mollusca's digestive system would be the use of cilia. Cilium are short eyelashlike filament that are numerous on tissue cells of most animals especially the Mollusca animals. They are used for movement are are inside all the digestive tracts providing movement for various reasons. Mainly because the digestive tracts of Mollusca are primitive and need external forces to churn and move the food when other developments have not been made to do so. The use of a radula is common among the majority of Mollusca but not all, and is gone through in more detail in the Garden Snail tag. -T.J. Gray
Helix aspersa, Garden Snail
The first part of the Garden Snail's digestive system is the buccal mass. This is comprised of the mouth and the pharynx. The mouth of the snail has an adaption called the radula. The radula can be described as toothed ribbon which the snail uses for scraping and cutting food, for this snail that would be plants. There is also a jaw on the snail that basically keeps the food still while the radula tries to cut off pieces of it. Then there are ducts that protrude from large salivary glands that into the mouth and the oesophagus of the snail. Digestive enzymes are added from these ducts to help break down the food. The stomach in the snail is a basic sac where the main part of the digestion takes place. The farthest part of the stomach is lined with cilia to help with the movement of the food. This part of the stomach rotates pushing the food forward steadily. Then there are two glands that come from the stomach that add digestive acids that help break down the food. At the end of the stomach there is an opening which then goes into a coiled intestine. This intestine helps re-absorb the moisture from the food particles. This then produces pellets. The anus hole is not in the back of the snail but the hole opens up above the head. An intriguing location to say the least. |
•Histioteuthis reversa (Cock-Eyed Squid)
Squids have a very muscular stomach found in the middle of the visceral mass. (The top-hat head on the squid.) After the bolus moves away from the stomach it enters into the organ known as the caecum for digestion. The bolus is a mass of food that has been chewed at the point of swallowing. The caecum is the pouch at the beginning of the large intestine where most of the digestion and absorption of nutrients takes place. After the digestion the bolus moves through the rest of the intestines. The bolus makes a 180' turn back the other way and is consolidated in the colon. The feces are then pushed through the anal. In male squids reproduction is seen as a more important function than digestion so when a male has become fertile the stomach and other digestive organs shrink in size to make room for reproductive organs. This process continues until death where the older male squid has a very small, shriveled stomach when compared to a female's stomach which does not shrink. |
•Margaritifera margaritifera (Freshwater Pearl Mussel)
The digestive tract of the Freshwater Pearl Mussel starts out with the incurrent sucking plankton into its shell. Inside it enters into the mouth of the mussel. Something cool about that is the mouth of the mussel is actually inside the mussel's shell! After the food enters through the mouth it goes through an esophagus into the stomach chamber. Rotating cilia in the stomach sac swirls the food in the stomach until the smaller pieces of food enter into the digestive glands, and the bigger pieces go into the intestines. In the intestines the larger pieces are broken down more with acidic acids and the nutrients are absorbed. The physical waste is then compressed in the rectum and pooped out as pellets through the anal opening. The excretion of waste and and the feeding of plankton and other microscopic organisms in the Freshwater Pearl Mussel depends on the current and waves of the body of water it is in. In a way the mussel does not have control over whether it is eating or excreting, but the water does. |