The phyla Annelida includes ringed or segmented worms. The phyla includes over 17,000 species such as ragworms, earthworms, and leeches ("Annelid: The Official Worms").
Annelids have an unsegmented gut that is located in the middle of the body. This gut runs from the organism's mouth to the anus. The coelom separates the gut from the body wall ("Annelid: The Official Worms"). Coelom:
Role of Evolution: If the worm is punctured, it loses its ability to move properly, since functioning of the body muscles is dependent on the maintenance of the fluid volume in the coelom. In primitive annelids each compartment of the coelom is connected to the outside by ducts for the release of sex cells, and by paired excretory organs, or nephridia. These openings are closed except when functioning, thus preventing the loss of coelomic fluid. In more advanced species both excretory and reproductive functions are sometimes served by a single type of duct, and ducts may be absent in certain segments ("Annelid: The Official Worms"). |
Ragworm DigestionRagworms use their net-like mouth and jaws to eat their food. From the mouth, the food directly travels through from the mouth to the anus, without stopping. The food travels from the mouth, into the esophagus, and then the intestine. Nutrients from the food are provided to the worm, and the excess waste is released through the anus ("Annelida").
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Leech DigestionLeeches' use their blade-like jaws to slice the skin of their host. The leech's mouth is located behind these blades. The mouth then leads to the esophagus, crop, gizzard, and intestinum. The crop acts as an expandable storage compartment. The leech also produces an anticoagulant that prevents the blood stored in their body from clotting ("Annelida").
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Earthworm Digestion
The digestive system is partitioned into many regions, each with a certain function. The digestive system consists of the pharynx, the esophagus, the crop, the intestine and the gizzard. Food such as soil enters the earthworm’s mouth where it is swallowed by the pharynx. Then the soil passes through the esophagus, which has calciferous glands that release calcium carbonate to rid the earthworm’s body of excess calcium. After it passes through the esophagus, the food moves into the crop where it is stored and then eventually moves into the gizzard. The gizzard uses stones that the earthworm eats to grind the food completely. The food moves into the intestines as gland cells in the intestine release fluids to aid in the digestive process. The intestinal wall contains blood vessels where the digested food is absorbed and transported to the rest of the body ("Annelida").