Annelida Members of the phylum Annelida are segmented worms, such as the earthworm. The segmented worms all display bilateral symmetry, cephalization, an open digestive system, segmentation, and a body cavity. The body cavity is a true body cavity called a coelom . This is a fluid-filled space between the innermost cell layer and the outer two cell layers. In this space, the reproductive and digestive organs have evolved into complex structures with complex functions. Also the digestive system is cushioned in the coelom, so the activities of the digestive system take place without interacting with the inner or outer body walls. Earthworms and other annelids have numerous segments, each separated from the others by internal partitions. Funnel-shaped excretory units called nephridia , located in most of the segments,
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