2. Phylum Cnidaria - Jellyfish, Sea Anemones, Coral, and Hydras. Cnidarians show radial symmetry Are carnivores, with cnidocytes(stinging cells) on their tentacles. Consist of more than 10,000 mostly marine species Have a body plan that is a sac with a central digestive compartment, the gastrovascular cavity. This cavity functions as a mouth and as an anus. Two body forms: the sessile polyp attaches to a substrate, and the free- floating medusa.

Cnidocytes, and Purple Striped Jellyfish Jellyfish How a Cnidocyst Stinging Cell Works

3. Phylum Platyhelminthes-Flat Worms-Tapeworms, Flukes, & Planaria Flatworms are the simplest bilateral animals. Range from about 1 millimeter (mm) to about 20 meters in length. Live in marine, freshwater, and damp terrestrial habitats Include many parasitic species including flukes and tape worms. Tapeworms have a ribbon like body which can be up to 20m long in humans. Lack a digestive tract, so they absorb partially digested food from the intestines of their hosts. Humans can become infected with tapeworms by eating undercooked beef. Watch 4 minute tape of fisherman with a parasitic friend.

4. Phylum Nematoda-Round Worms Roundworms get their common name from the cylindrical bodies tapered at both ends. Roundworms are among the most diverse and widespread animals Roundworms consist of about known species (perhaps 10 times more actually exist). Range in length from 1mm to 1 meter, Live in most aquatic habitats, in wet soil, and as parasites in the body fluids and tissues of plants and animals. Exhibit a complete digestive tract with a mouth and anus. Have a body cavity; pseudocoelom. Humans host at least 50 parasitic species including: pinworms, hookworms, and the parasite which causes trichinosis. A free-living roundworm Nematode

5. Phylum Annelida-Segmented Worms- Earthworms, Polychaetes, & Leeches Annelids are worms with body segmentation, the division of the body along its length into a series of repeated parts. Annelids consist of about 15,000 species. Range in length from 1mm to 3 meters long. Live in the sea, most freshwater habitats, and damp soil. The three major classes of annelids are earthworms, polychaetes, and leeches. Farmers value the earthworm because they eat their way through the soil, extracting nutrients, tilling the soil, and producing castings which improve the texture of the soil. Giant Earthworm Darwin estimated that an acre of British farmland has about 50,000 earthworms which produce about 18 tons of castings per year.