Phylum Annelida (segmented worms) 2009.pdf

Phylum Annelida (segmented worms) 2009.pdf

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Annelida (L. annulus = little ring) Segmented body (metameric) 1. Coelom divided by septa 2. Chitinous setae 3. Circular and longitudinal muscles 4. Closed circulatory system 5. Solid ventral nerve cord 6. Respiration through skin, gills or parapodia 7. Metanephridial excretory system 8. Classes of Annelida Polychaeta Many setae in parapodia Separate sexes Mostly marine Oligochaeta Few setae, no parapodia Clitellum Hermaphroditic Hirudinea No setae nor parapodia Clitellum Hermaphroditic Metamerism: serial repetition of segments (somites) along the length of the animal Criteria of true metamerism: Mesodermal origin 1. Embryonic development 2. Penultimate budding 3. What are the advantages of metamerism? More efficient locomotion Functional independence among segments Provides a framework for specialization
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