Annelids, or segmented worms, have bilateral symmetry and a body cavity containing organs. Earthworms have over 100 segments and move using setae and muscles. They ingest soil, grind it, and excrete waste to aid the soil. Earthworms have a closed circulatory system and exchange gases through their skin. They are hermaphrodites that need to mate to reproduce. Marine worms have segments with bundled setae, with some free-moving and others building tubes. Leeches lack setae and feed on blood, being used medicinally to prevent coagulation and study treatments. Segmented worms are valuable as they aerate soil, produce medicines, and provide food.

1. Segmented Worms Chapter 13 Section 2

3. 1. Earthworms ingest soil which moves to the crop for storage, then to the gizzard for grinding, then to the intestine; wastes exit the anus and help the soil.

4. 2. Earthworms have a closed circulatory system and exchange oxygen and carbon dioxide through skin covered with watery mucus.

5. 3. Earthworms have a small brain and nerves in each segment, joining to a main nerve; they are hermaphrodites that must exchange sperm with another earthworm to reproduce.