Annelids are bilaterally symmetrical, segmented schizoatecoelomates. About 17,000 species have been described, common species include earthworms, leeches, lugworms, etc. Body length ranges from a few millimeters to 3 meters. Inhabiting the ocean, fresh water or moist soil, it is the most dominant lurking animal in soft substrate habitats. A few live parasitically in the camp. Divided into 3 classes: Polychaeta, Oligochaeta and Bleeding Class.