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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 freefloating 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 90.000 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 Giant Earthworm Darwin estimated that an acre of British farmland has about 50,000 earthworms which produce about 18 tons of castings per year. • 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.