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Annelida Segmented Worms Phylum Annelida General Characteristics Includes duster worms, tube worms, earthworms, & leeches Bilateral symmetry Soft-bodied with divisions called metameres (ring-like segments) 15,000+ species; marine, fresh water, and soil Most are free-living, capturing live prey or scavenging; some live in burrows or tubes; some are parasites Body segments covered with setae (bristle-like structures), used for movement, anchorage, or burrowing Phylum Annelida General Characteristics Internal organ systems such as blood vessels, muscles, and nerves repeated in each body segment (septa: internal segments) Coelomates with hydrostatic skeleton Triploblatic: Endoderm, Mesoderm, and Ectoderm One way digestion: mouth and anus Anterior end or head (prostomium) typically equipped with mouth and jaws, eyes and other sense organs Phylum Annelida General Characteristics Body wall has layers of circular and longitudinal muscles that enable worm to extend and shorten Nervous system: cerebral ganglion (“brain”), two ventral nerve cords Closed circulatory system: 5 aortic arches (“hearts”) pump blood into ventral vessel Secrete mucus to keep skin moist and exchange gases through diffusion Filter wastes from blood through nephridia (ciliated paired tubules) Phylum Annelida Classes of Annelids Polychaeta – Nereis (clam worms), Arenicola (lugworms), bloodworms, sandworms Oligochaeta – Lumbricus (earthworms), Tubifex (sludge worm or sewage worm) Hirudinea – Hirudo (medicinal leech) Phylum Annelida Class Polychaeta Mostly marine Parapodia (lobes w/setae and other parts) Cuticle 1st segment – prostomium (bears eyes, tentacles, and sensory palps) 2nd segment – peristomium (surrounds mouth) Phylum Annelida Polychaeta Feeding Most carnivorous – Some have venom – Gut is straight tube Some are detritovores – Extract nutrition from sediment (or soil) Many are filter feeders Some can get food by diffusion Phylum Annelida Other polychaete Systems Respiration by diffusion 2-4 pairs of eyes on/near prostomium Metanephridium for excretion Phylum Annelida Polychaete Reproduction Can regenerate Asexual reproduction – Budding Sexual reproduction – Most fertilization external Phylum Annelida Oligochaeta (“few long hairs”) Terrestrial, freshwater, some marine Have a clitellum – For mucus secretion – Used in copulation – Used to form cocoons No parapodia Few setae Phylum Annelida Oligochaete Locomotion Use circular and longitudinal muscles Can use setae as anchors Use hydrostatic pressure Scavengers and/or detritovores Path of food – – – – – – – Mouth Pharynx (helps suck up food) Crop (storage) Gizzard (grinds food up) Stomach (digestion) Intestine (absorption of nutrients) Anus (castings) Phylum Annelida Other Oligochaete Systems Simple brain with dorsal and ventral nerve cords Sensitive to light, touch, moisture, chemicals, temperature, & vibrations Use metanephridia for excretion Chloragogen tissue (surround intestine, serve in synthesis of glycogen and fat = liver cells) Phylum Annelida Oligochaete Reproduction Hermaphroditic Must line up clitella Held together by mucus sheath Cocoon formed – Fertilization occurs here – No larval stages – Clitellum only present in sexually mature Some freshwater species asexual Phylum Annelida Hirudinea Terrestrial, freshwater or marine No parapodia Circular, longitudinal and oblique muscle layers Phylum Annelida Hirudinean Feeding Many carnivorous – Eat Small invertebrates – Suck Body fluids Mouth in the anterior sucker Gut specialized for storage of large quantities of blood Produce “hirudin” – anticoagulant (prevents blood from clotting) Phylum Annelida Other Hirudinea Systems Gas exchange by diffusion Nervous system – Photoreceptors – Can sense temperature – Sensory papillae 10-17 pairs of metanephridia for waste Chloragogen tissue Phylum Annelida Hirudinea Reproduction All hermaphroditic All sexually reproducing Have a penis for sperm transfer Clitellum seen during breeding season No larval stages Phylum Annelida Economic Importance Castings and burrows help root growth, aeration, and drainage of crops Grinding of soil by gizzard + secretions improves soil structure and quality Earthworms bring organic molecules into the soil Fish bait Leeches are used in medicine for circulation: prevents gangrene Phylum Annelida