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Phylum Annelida: Segmented Worms • Body composed of segments separated by internal partitions (appears as little rings around the body of the worms) • Greek word “annellus” means little ring • Includes earthworms, exotic seafloor worms, and leeches Segmented Worms Body Systems Circulation • Have a closed circulatory system that includes vessels Respiration: • Aquatic annelids breathe using gills • Terrestrial annelids diffuse oxygen through their moist skin Segmented Worms Body Systems Nervous System • Most annelids have a well developed nervous system consisting of a brain and several nerve cords Digestion • Digestion occurs as food passes through a tube-like digestive system with two ends (mouth and anus) • Range from filter feeders to fearsome predators (at least for their size) Movement of Segmented Worms Have longitudinal and circular muscles • Longitudinal muscles run parallel to the length of the worm and contract to make the worm shorter and fatter • Circular muscles wrap around each body segment and contract to make the worm longer and thinner • Movement is obtained by alternating contractions of these muscles Segmented Worm Reproduction Sexual Reproduction Only! • Typically includes a male and female • Segmented worms are hermaphroditic • Fertilization occurs externally External Fertilization • Two Hermaphroditic individuals swap sperm simultaneously • The sperm are stored in special sacs on the body until the eggs are ready for fertilization • The eggs and sperm are released into a mucus ring that slips off the end of the worms’ body and forms a protective cocoon • Young hatch two to three weeks later Classes of Annelids Class Oligochaeta – (Oligochaetes) – earthworms and their relatives found in soil and fresh water Class Hirudinea – leeches; parasites that suck blood. – Most feed on snails, worms, and insect larvae Class Polychaeta – (Polychaetes) – sandworms and bloodworms Earthworms: Friend or Foe? • Spend their lives burrowing in soil, aerating it, and mixing it to depths of two meters or more. • But do they decrease the amount of duff (organic matter; leaves) leading to changes in the ecosystem