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• True coelom that is lined • Segmented bodies • Septa: internal walls between each segment • Setae: bristles that are attached to each segment; used in respiration • Filter feeders to predators • Get their food using a pharynx • Crop: in earthworms; part of the digestive system in which food can be stored • Gizzard: in earthworms; part of the digestive system in which food is ground into smaller pieces • Have complex organ systems • Segmented body • Closed circulatory system: blood is contained within a network of blood vessels • Blood circulates through two major blood vessels that run from head to tail • Aquatic annelids: gills • Land-dwelling annelids: diffusion through their moist skin • Two kinds of waste • Digestive waste passes out through the anus at the end of the digestive tract • Nephridia: excretory organs that filter fluid in the coelom • Well-developed nervous system consisting of a brain and several nerve cords • The sense organs are best developed in free-living marine annelids • Hydrostatic skeleton • Longitudinal muscles and circular muscles • Moves by alternating contracting these two sets of muscles • Sexually • Some use external fertilization or have separate sexes • Others, such as earthworms and leeches, are hermaphrodites – Exchange sperm – Clitellum: a band of thickened, specialized segments that secretes a mucus ring into which eggs and sperm are released and fertilization occurs – The ring slips off the body and form a protective cocoon for the worms that hatch a week later • Oligochaetes – Streamlined bodies and have relatively few setae compared to polychaetes, live in soil or fresh water • Leeches – External parasites that suck the blood and body fluids of their host • Polychaetes – Marine annelids that have paired, paddlelike appendages tipped with setae • Provide passageways for plant roots and water and allow the growth of beneficial, oxygen requiring soil bacteria • Important in the diet of many birds, moles, skunks, toads and snakes • In the sea they participate in a wide range of food chains Segmented Worms True coelomates; cephalized Digestive tract with mouth & anus (tube-within-a-tube) Closed circulatory system (blood contained in vessels) Segmented body Mouth Most are marine, but many live in freshwater Gut Examples: Earthworms Leeches Deep ocean Anus tube worms Ectoderm Mesoderm Endoderm Annelids 3 germ layers Coelom