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"jellyfish," 1758, as genus name, from the name of one of the three Gorgons with snakes for hair, whose glance turned to stone him who looked upon it (attested in English from late 14c.). Her name is from Greek Medousa, literally "guardian," fem. present participle of the verb medein "to protect, rule over" (see Medea). The zoological name was chosen by Linnæus, suggested by the creature's long tentacles. Related: Medusoid.
Plural medusas or medusae (mĭ-d'sē)
A cnidarian in its free-swimming stage. Medusas are bell-shaped, with tentacles hanging down around a central mouth. Jellyfish are medusas, while corals and sea anemones lack a medusa stage and exist only as polyps. Compare polyp.