Marine coelenterates (class Hydrozoa) including some poisonous species, notably Physalia, the Portuguese man-of-war; toxin is injected into the skin by nematocysts on the tentacles, causing linear wheals. SYN: jelly (2).
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jel·ly·fish 'jel-ē-.fish n a free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells
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jel·ly·fish (jelґe-fish) 1. the medusa stage, a stage in the life cycle of certain invertebrates of the phylum Cnidaria, class Scyphozoa, when their bodies are transparent and umbrella-shaped and the organisms are free-swimming; the body can vary between species from a few millimeters to two meters in diameter. Genera that inflict poisonous stings include Aurelia, Carukia, Chironex, and Chiropsalmus. 2. the term is also used for certain other cnidarians that have a medusalike stage, such as members of the genera Gonionemus and Physalia.Medical dictionary. 2011.