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Lecture 5 Animal Evolution – The Invertebrates. 2. Cnidarians. Have simple tissues, no organs Radial symmetry, tentacled, with sac-like gut, epithelia, a nerve net, epithelia & hydrostatic skeleton. Live in seas. Jellyfishes, sea anemones, hydra & corals. 2 common body plans/structure:
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2. Cnidarians • Have simple tissues, no organs • Radial symmetry, tentacled, with sac-like gut, epithelia, a nerve net, epithelia & hydrostatic skeleton. • Live in seas. • Jellyfishes, sea anemones, hydra & corals. • 2 common body plans/structure: • Medusa (medusae; plural) • Polyps
Medusae: float & look like bells/saucers. Mouth centered under the bell, often with tentacles & other extensions for prey capturing & feeding. Polyps: Tube shaped, usually attaches to substrate Tentacle-ringed mouth at one end, captures prey. Cnidarian gut-permanent food-processing chamber. Medusa vs Polyps