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Phylum Cnidaria • Cnidarians (phylum Cnidaria) are multicellular animals with tissues that perform specific functions • Cnidarians include the sea anemones, jellyfish, coral, and their relatives • Cnidarians have radial symmetry; in fact radial symmetry evolved in the Cnidarians! Cnidarians are rad! • Animals with radial symmetry look the same from all sides and have no head, front or back • Instead have an oral surface (where mouth is) and aboral surface Phylum Cnidaria • Cnidarians have a centrally-located mouth surrounded by tentacles, slender, finger-like projections used to capture and handle food • All possess stinging cells, or nematocysts • Nematocysts employ neurotoxins which paralyze prey; 7-17 different types • The mouth opens up to a gut, with only one opening Nematocysts http://www.youtube.com/watch?v=BpKKGBivQo&feature=related Phylum Cnidaria • Cnidarians occur in two basic forms: a polyp, a sac-like attached form with its mouth and tentacles pointed upward, and a bell-like medusa, which resembles an upside-down polyp adapted to swimming • Some Cnidarians have both polyp and medusa stages; others spend their entire lives as either a polyp or a medusa