Phylum Coelenterata (Cnidaria) The phylum is divided into three large classes: Hydrozoa (hydras, Portuguese man-of-war), Scyphozoa (true jellyfish), and Anthozoa (soft corals, stone corals, anemones) Coelenterata have tentacles with specialized organelles called nematocysts, which are used for entangling, penetrating, anchoring, and poisoning prey ( Fig 90.15 ) When the tentacles touch an object, the nematocysts fire, releasing toxin-coated, barbed threads The severity of envenomation is related to venom toxicity, number of nematocysts discharged, and general condition of the victim Stings from sessile forms are generally not as severe as stings from free-floating forms Jellyfish venoms affect autonomic nervous systems via several mechanisms Paralysis and CNS effects appear to be related primarily to toxic proteins and peptides Burning pain and urticaria are caused by the release of various mediators of inflammation, including serotonin and histamine