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Phylum Annelida (Taxonomic Divisions (Class Polychaeta (polychaetes)…
Phylum Annelida
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Body Systems
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Circulation
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Closed circulatory system -- Dorsal blood vessel -- ventral blood vessel -- capillary networks --may have aortic arches
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Nervous System
Anterior, dorsal BILOBED brain...a pair of central ganglia
Longitudinal nerve cords leave each ganglion, travel around the pharynx (circumpharyngeal connectives) adn combine to travel along the ventral surface... Double ventral nerve cord
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Leeches have another pair of ganglia at the posterior end (posterior brain) to control posterior sucker
Sensory System
Some with simple, single celled or clustered photoreceptors --> ocelli
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Body Structure
Most are long worm-like with three body regions:
-- head - with some degree of cephalization
-prostomium-with tentacles, palps, and sensory structures
-peristomium-behind postomium contains the mouth, may have pharynx and chitinous jaws
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Most have paired appendages on most segments....parapodia
--used for locomotion and respiration
--in some, may be modified into fans and mucus bags for feeding or to create water currents
Epidermis - single layer of columnar epithelial cells -- secretes a thin and flexible cuticle of chitin -- secretes bristle like setae or chaetae
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