Phylum Annelida (Chapter 27.3) Please set up your notebook for Cornell Notes

Annelids Characteristics Body divided into segments separated by walls called septa Have a coelom  coelomates Some worms have bristles called setae attached to each segment Have mouth and anus, digestive tract Triploblastic  three germ layers

Form and Function Feeding and digestion Filter feeders, predators, decomposers Have a pharynx Pharynx has jaws in carnivores Pharynx covered in sticky mucus in decomposers Pharynx pumps food and soil into esophagus Crop – stores food Gizzard – grinds food into smaller pieces Food absorbed in intestines

Circulation Annelids have a closed circulatory systems Two major blood vessels No heart – dorsal blood vessel contract and circulates blood Respiration Aquatic annelids breathe using gills feathery structures used to exchange gases underwater Land dwelling annelids diffuse gases through moist skin

Excretion Digestive waste passes out of the anus Nitrogenous waste is excreted through the nephridia  organs that filter fluid in coelom Response Most annelids have a brain and several nerve cords Marine annelids have many sensory adaptations Sensory tentacles, chemical receptors, statocysts, eyes

Movement Two major groups of muscles Longitudinal  contract to make the worm shorter and fatter Circular  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 annelids Class Oligochaeta Stream-lined bodies with very few setae Mostly live in soil and fresh water Earthworms and tubifex worms

Class Hirudinea External parasites that suck blood and body fluids Leeches Live in moist habitats in tropical countries Have powerful suckers at both ends Posterior  attachment Anterior  Eating

Class Polychaeta Marine annelids w/ paired, paddle-like appendages that have setae on the tip Sandworms, blood worms Live in cracks in coral reefs, in sand and mud and open water