Annelida: Oligochaete Digestion

Oligochaete Digestion

The mouth, located under the head, leads to a relatively simple, straight digestive tract consisting of a pharynx, an esophagus, and an intestine, terminating in an anal opening. Terrestrial oligochaetes tunnel through the ground, swallowing soil as they go. The digestive tract of such a worm is specially modified for this rough diet. Typically it has a thin-walled storage area, or crop, and a muscular gizzard for grinding the soil to remove the organic matter that is the actual food of the worm. Specialized calciferous glands remove excess calcium, magnesium, strontium, and phosphate and regulate the level of these ions in the blood. Solid wastes are egested and plastered against the burrow wall, or ejected from the mouth of the burrow; the ejected material is called castings. Earthworms, through their burrowing and digestive processes, are largely responsible for the mixing and aeration of the soil. Not all oligochaetes have soil diets; some of the small aquatic worms are active predators on other small invertebrates. Excretion is typically carried out by a pair of tubes in each segment.

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