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Download Zoo Ch 37-2 Annelida
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CHAPTER 37-2 Annelida Phylum: Annelida Annelid: means “little rings” Many body segments Can include marine species Earthworms Leeches Characteristics and Classification Bilateral Symmetry Coelomates Segmented (important evolution) Developed organ systems External Bristles and Fleshy Protrusions Setae # Parapodia Presence Determine or absence which class division Oligochaeta, Polychaeta, Hirudinea Oligochaeta Live in soil or fresh water Look for adaptations for burrowing Have no parapodia Name means “few bristles” Have few Setae Most familiar member is the Earthworm Oligochaeta – Structure and Movement Earthworm body divided in more than 100 virtually identical segments Locomotion method Worm anchors some middle segments by setae Contracts muscles in front of those segments This increases pressure on coelomic fluid Elongates the animal and pushes anterior end forward Anterior setae then grip ground, pulling the posterior segments forward Oligochaeta – Feeding and Digestion Ingest soil as they burrow through Sucked into mouth by the pharynx Esophagus – crop – gizzard – intestine - anus Play an important role to maintain soil fertility Decomposition Release nutrients Oxygen penetration Loosen soil Oligochaeta – Circulation Closed circulatory system Blood travels to posterior end through ventral blood vessel Blood returns to anterior end through dorsal vessel Aortic arches link the two blood vessels at the anterior end Oligochaeta – Respiration and Excretion No specialized respiratory organs Oxygen and CO2 diffuse directly through skin Gas exchange only happens if skin is moist Secrete mucus and have a thin cuticle Eliminate cellular waste and excess water Excretory tubules called nephridia Each segment (except first 3 and last 1) contain a pair Nephridia Oligochaeta – Neural Control Nervous system Chain of ganglia connected by a ventral nerve cord Most segments contain a single ganglion Nerves Several Main branch from each ganglion ganglia fused to form “brain” (cerebral ganglia) function is to process simple info from sensory structures Present in all segments, but concentrated at anterior Oligochaeta – Reproduction Hermaphrodites (Cannot self fertilize) Mating: 2 worms press ventral surface together, anterior pointing in opposite directions Held together by: Setae & Mucus Secreted by clitellum (thickened section) Sperm moves through mucus to seminal receptacle Oligochaeta – Reproduction Cont’d The worms separate After several weeks the clitellum secretes a tube Made of mucus and chitin Tube slide forward and picks up eggs and sperm Fertilization occurs within tube Young worm develops inside for 2-3 weeks before hatching Polychaeta 2/3 of all annelids “many bristles” Mostly marine Have antennae and specialized mouthparts Hirudinea Smallest class, about 300 species Leeches Mostly freshwater No setae or parapodia Sucker at each end of body Some are carnivores, but many are parasitic Suck blood from host Secrete anesthetic and anti-clotting substance
