Pediatric emergency medicine trisk 1993 1993
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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.
