Phylum Annelida Segmented Worms

Symmetry Bilateral No backbone

Characteristics Have setae, crop, gizzard, mouth, and anus Closed circulatory system Tiny brains and nervous systems Hermaphroditic Body cavity for organs

Examples Earthworms Leeches Bristle worms

Leeches Are segmented worms but body is not as round or as long as earthworms They don’t have setae Feed on blood of other animals Leeches produces an anesthetic so you don’t feel it when they bite Can suck out blood two to ten times its own body weight Can survive off eating aquatic insects or other organisms

Leeches & Medicine Used after surgery to keep blood flowing to the repaired area They secrete a chemical that acts like an anti coagulant and doesn’t allow the blood to clot They also produce a chemical that dilates the blood vessel to help with the flow of blood

Value of Segmented Worms Earthworms help to aerate the soil and get nitrogen back in the soil faster Researchers are developing drugs based on the chemicals produced by leeches Small marine worms and their larvae are part of ocean plankton and are food for other organisms

Origin of Segmented Worms Scientists hypothesize that they evolved from the sea Because of their soft bodies fossil records are limited Similarities between mollusks and segmented worms suggest that they have a common ancestor –First animals to have a body cavity for organs –One way digestive systems, with separate mouth and anus –Similar larvae