1. 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

2. 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

3. 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)

4. 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

5. Segmented Worm Reproduction Sexual Reproduction Only! Typically includes a male and female Segmented worms are hermaphroditic Fertilization occurs externally

6. 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

7. 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

8. 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