With plural agreement: a former class of coelenterate organisms including jellyfish, comb jellies, siphonophores, and (originally) sea anemones. With singular agreement (also in form acalepha): an animal of this class (usually in plural, the animals of this class collectively).
Introduced by Cuvier as a subdivision of Radiata; the sea anemones were later moved to the class Polypi. By some later authors restricted to the Scyphozoa or true jellyfish.
Early 19th century; earliest use found in John Fleming (1785–1857), naturalist and Free Church of Scotland minister. Partly from scientific Latin Acalepha, class name, alteration of Acalephae; and partly from scientific Latin Acalephae, class name, feminine plural from ancient Greek ἀκαλήϕη stinging nettle, sea anemone (so called on account of its stinging properties), of unknown origin.