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Jellyfish or jellies〔Van Patten, Peg. ("Sting" ). (2004). Wrack Lines. Paper 11.〕 are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey. Jellyfish are found in every ocean, from the surface to the deep sea. Scyphozoans are exclusively marine, but some hydrozoans live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years,〔(Fossil Record Reveals Elusive Jellyfish More Than 500 Million Years Old ). ScienceDaily (2 November 2007).〕 and possibly 700 million years or more, making them the oldest multi-organ animal. == Terminology == The English popular name ''jellyfish'' has been in use since 1796.〔 It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores (members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as ''comb jellies'') were included as "jellyfishes". Even some scientists include the phylum ctenophora when they are referring to jellyfish.〔 〕 Other scientists prefer to use the more all-encompassing term ''gelatinous zooplankton'', when referring to these, together with other soft-bodied animals in the water column. As jellyfish are not true fish (which are vertebrates, unlike jellyfish), the word ''jellyfish'' is considered by some to be a misnomer. Public aquariums may use the terms ''jellies'' or ''sea jellies'' instead.〔(''Flower Hat Jelly'' ), New York Aquarium.〕 The term "jellies" may have become more popular than "jellyfish".〔 In scientific literature, "jelly" and "jellyfish" are often used interchangeably.〔See, e.g., Brotz, Lucas. (Changing Jellyfish Populations: Trends in Large Marine Ecosystems ). 2011. p.1.〕 Some sources may use the term "jelly" to refer to organisms in this taxon, as "jellyfish" may be considered inappropriate. Many textbooks and sources refer to only scyphozoa as "true jellyfish". A group of jellyfish is sometimes called a bloom or a swarm. "Bloom" is usually used for a large group of jellyfish that gather in a small area, but may also have a time component, referring to seasonal increases, or numbers beyond what was expected.〔(【引用サイトリンク】title= Jellyfish Take Over an Over-Fished Area )〕 Another collective name for a group of jellyfish is a ''smack'',〔"''Smack: a smattering; a taste; a small quantity. Examples: smack of jellyfish – Lipton, 1970; of knowledge; of my muse, 1766; ...''" from (The Free Dictionary ). For more detail see (An exaltation of larks ) by James Lipton.〕 although this term is not commonly used by scientists who study jellyfish. Jellyfish are "bloomy" by nature of their life cycles, being produced by their benthic polyps usually in the spring when sunshine and plankton increase, so they appear rather suddenly and often in large numbers, even when an ecosystem is in balance. Using "swarm" usually implies some kind of active ability to stay together, which a few species such as ''Aurelia'', the moon jelly, demonstrate. Medusa jellyfish may be classified as scyphomedusae ("true" jellyfish), stauromedusae (stalked jellyfish), cubomedusae (box jellyfish), or hydromedusae, according to which clade their species belongs. The term ''medusa'' was coined by Linnaeus in 1752, alluding to the tentacled head of Medusa in Greek mythology.〔(jellyfish ). Online Etymology Dictionary. Etymonline.com. Retrieved on 2013-01-10.〕 This term refers exclusively to the non-polyp life-stage which occurs in many cnidarians, which is typified by a large pulsating gelatinous bell with long trailing tentacles. All medusa-producing species belong to the sub-phylum Medusozoa. In biology, a ''medusa'' (plural: medusae) is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below. The upper or aboral surface is called the ''exumbrella'' and the lower surface is called the ''subumbrella''; the mouth is located on the lower surface, which may be partially closed by a membrane extending inward from the margin (called the ''velum''). The digestive cavity consists of the gastrovascular cavity and radiating canals which extend toward the margin; these canals may be simple or branching, and vary in number from few to many. The margin of the disk bears sensory organs and tentacles. German biologist Ernst Haeckel popularized medusae through his vivid illustrations, particularly in ''Kunstformen der Natur''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「jellyfish」の詳細全文を読む スポンサード リンク
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