Research Article Summary

Annelida is a phylum of soft bilaterally symmetrical worms. 12,000 species of Annelida is grouped into three classes: the oligochaetes [earthworms and freshwater worms], hirudineans [leeches], and the polychaetes [marine worms]. You can find these segmented worms in mud, sand, and rock crevices and among many other things even a sponge. The body of an annelid consists of a head, a trunk, and a section of the body called a pygidium which is unsegmented. Their body wall consists of muscles that assist the annelid in crawling and swimming. They also possess short bristles called setae that are used to grip the soil to hold the animal in the tube and/or assist it in swimming.

The annelids digest through a single gut that runs through the middle of their body and is separated from their body wall by coelom which is the worm’s body cavity. The body cavity works as a skeleton in the annelids except for the leeches. The annelid’s muscles depend on the fluid found in their body cavity to function properly. Reproduction in annelids is either sexual or asexual. In most annelids, respiration occurs directly through their body wall because they have no special organs for gas exchange. However some aquatic annelids have gills used for respiration. The nervous system of an annelid consists of a brain which is connected by nerves to a nerve cord that runs throughout their body. The sense organs of annelids include eyes, taste buds, tentacles, and equilibrium organs. Circulation throughout the annelids body occurs through the containment of a red-oxygen carrying pigment, a green-oxygen carrying pigment, or some have unpigmented blood. The system is usually confined within blood vessels or the system is found partially open in some annelids such as the leeches.