Post on 01-Jan-2016
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Phylum Annelida (Chapter 27.3)Please set up your notebook for Cornell Notes
AnnelidsCharacteristics
Body divided into segments separated by walls called septaHave a coelom coelomatesSome worms have bristles called setae attached to each segmentHave mouth and anus, digestive tractTriploblastic three germ layers
Form and FunctionFeeding and digestion
Filter feeders, predators, decomposersHave a pharynx
Pharynx has jaws in carnivoresPharynx covered in sticky mucus in decomposersPharynx pumps food and soil into esophagus
Crop – stores foodGizzard – grinds food into smaller pieces
Food absorbed in intestines
CirculationAnnelids have a closed circulatory systems
Two major blood vesselsNo heart – dorsal blood vessel contract and circulates blood
RespirationAquatic annelids breathe using gills feathery structures used to exchange gases underwaterLand dwelling annelids diffuse gases through moist skin
ExcretionDigestive waste passes out of the anusNitrogenous waste is excreted through the nephridia organs that filter fluid in coelom
ResponseMost annelids have a brain and several nerve cordsMarine annelids have many sensory adaptations
Sensory tentacles, chemical receptors, statocysts, eyes
MovementTwo major groups of muscles
Longitudinal contract to make the worm shorter and fatterCircular contract to make worm longer and thinner
Marine annelids have paddle-like appendages called parapodia on each segment used for swimming and crawling
Reproduction
Most annelids reproduce sexually
Some have separate sexes, and external fertilization
Others are hermaphroditic but do not fertilize their own eggs
Two worms attach to each other, exchange sperm and store for later
When eggs are ready, the clitellum secretes a thick mucus ring where eggs and sperm are deposited
Ring slips off and provides a cocoon for developing larva
Some annelids reproduce asexually through budding
Classes of annelidsClass Oligochaeta
Stream-lined bodies with very few setaeMostly live in soil and fresh waterEarthworms and tubifex worms
Class HirudineaExternal parasites that suck blood and body fluidsLeechesLive in moist habitats in tropical countriesHave powerful suckers at both ends
Posterior attachmentAnterior Eating
Class PolychaetaMarine annelids w/ paired, paddle-like appendages that have setae on the tipSandworms, blood wormsLive in cracks in coral reefs, in sand and mud and open water