Phylum Annelida

Phylum Annelida - Phylum Annelida Polychaeta Nearly all...

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Phylum Annelida Polychaeta Nearly all marine, few brackish and fw Head appendages: palps and antennae (tentacles); fleshy peristomial cirri; or none Each segment typically has pair of unjointed appendages: parapodia; and bundles of setae- spine-like structures from epidermal cells Parapodia: biramous- dorsal notopodium and ventral neuropodium, each with own setae o functions: locomotion, gas exchange, protection, anchorage, creation of water currents depends on region of body Dioecious Simple reproductive structures o Gametes grow from peritoneum Order Myzostomida adapted for symbiotic life Body Wall Thin cuticle of scleroprotein and mucopolysaccharide fibers Epidermis: columnar epithelium; often ciliated on parts Connective tissue, circular muscle, and longitudinal muscles under epidermis Peritonium: inner lining Coelom divided into left/right and is segmented within the trunk o Dorsal and ventral mesenteries separate members of each pair of coeloms o Muscular intersegmental septa isolate each pair from the next Lost or incomplete in some (continuous coelomic fluid here) Some have no coelomic lining altering hydraulic qualities Parapodia: evagination of wall; movable by oblique muscles (originate near ventral body midline); Large parapodia contain pair of chitinous and scleroproteinous supporting rods (acicula) Setae: can be retracted and extended Support and Locomotion Coelomic spaces: hydrostatic skeleton Tube provides protection and keeps animal oriented Feeding 3 types: raptorial, deposit, and suspension feeders Raptorial: hunting predators (nereids) locate prey by chemical or mechanical means, evert pharynx by contractions of body wall muscles increasing hydrostatic pressure in coelomic spaces, jaws gape, coelomic pressure released, jaws close, prey and proboscis retracted; some scavenge feeding on dead organic matter; some predatory sit and wait, then ambush
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Some live in tubes and detect presence of prey by chemosensory or vibration-sensory means Some have poison glands associated with jaws ( Glycera ) Direct deposit feeders: ingest substratum and digest organic matter (Arenicolidae); irrigate burrow by drawing water into open end through peristalsis, water liquefies sand at blind end (near mouth) and is ingested by proboscis Selective deposit feeders sort organic material from sediment prior to ingestion Suspension feeding in tube-dwellers (Serpulidae and Sabellidae) and some that live in permanent burrows: peristomial tentacles (radioles) as feeding structure; cilia drive water upward between pinnules (branches) of radioles, particles sorted into 3 sizes as carried into groove (smallest go to mouth, largest rejected, medium stored for tube building) Chaetopteridae filter water for food extracting suspended materials; notopodial fans create water current through burrow (these and some other segments have suckers from neuropodia); mucus bag produced by secretions from segment 12 captures
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Phylum Annelida - Phylum Annelida Polychaeta Nearly all...

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