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