Segmented worms are included in the group Annelida. In our city parks and yards as well as from the deepest marine sediments to the soils, annelids are found worldwide. Annelids were divided into three major groups that include Polychaeta, Oligochaeta and Hirudinea in 20th century. Their length is about 20 feet and width in the contracted state may exceed 2.5 centimeters. They are vermiform and having bilateral symmetry. More than 2 cell layers are on body. Their body cavity is divided by internal septa. A prosomium, a trunk and a pygidium are three sections of annelids body possesses. They are having closed circulatory system and having no true respiratory organs. Reproduction is generally sexual and or hermaphroditic.



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