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KINGDOM ANIMALIA Phylum Annelida Phylum Annelida Cylindrical, bilateral, & segmented True coelom Complete digestive system Closed circulatory system Body Plan Annelids have a true body cavity or coelom that is located between layers of mesoderm Annelids are the first major phyla showing segmentation (metamerism) which is advantageous to movement, safety, and tagmatization Feeding Annelids have a complete digestive system Their system contains mouth, pharynx, esophagus, crop, gizzard, intestine and anus They use muscles to help in the mechanical digestion of food Movement Each annelid segment contains its own longitudinal and circular muscles These muscles work antagonistically, such that when the longitudinal muscles contract the circular muscles relax and the segment become short and thick In contrast, when the circular muscles contract, the longitudinal muscles relax and the segment becomes long and thin Reproduction Oligochaetes are hermaphroditic and during copulation they line up facing in the opposite direction The clitellum secretes a mucous that holds the worms in place Later, the clitellum acts as a cocoon where the fertilized egg develops Classification Class Polychaeta (many hairs) Class Oligochaeta (few hairs) Class Hirudinae (leeches)
