cnidarian

cni·dar·i·an

(nī-dâr'ē-ən) pronunciation

n.
Any of various invertebrate animals of the phylum Cnidaria, characterized by a radially symmetrical body with a saclike internal cavity, and including the jellyfishes, hydras, sea anemones, and corals. Also called coelenterate.

adj.
Of, relating to, or belonging to the phylum Cnidaria.

[New Latin Cnīdāria, phylum name, from Greek knīdē, sea nettle.]

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cnidarian

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(click to enlarge)
Cnidarian body forms. A cnidarian may display either the sessile polyp form or the free-swimming (credit: © Merriam-Webster Inc.)

Any of about 9,000 species of mostly marine aquatic invertebrates, constituting the phylum Cnidaria (or Coelenterata), that are unique in possessing specialized stinging cells (cnidocytes) borne on the tentacles. Cnidocytes contain fluid-filled capsules (nematocysts) with a harpoonlike coiled thread used for stinging, paralyzing, and capturing prey. Cnidarians have no well-defined separate respiratory, circulatory, or excretory organs; their tissues, composed of two cell layers, surround a cavity known as a coelenteron (gastrovascular cavity), which is the basic internal organ. Tentacles surrounding the mouth are used to capture and ingest food. Cnidarians are carnivorous, feeding mostly on zooplankton but also on small crustaceans, fish eggs, worms, smaller cnidarians, and even small fish. Cnidarians range in size from nearly microscopic to more than 100 ft (30 m) long and more than a ton (910 kg) in weight. There are two basic body forms: the polyp (e.g., coral) and the medusa (e.g., jellyfish). See also hydra; Portuguese man-of-war; sea anemone.

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cnidarian

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IN BRIEF: n. - Radially symmetrical animals having saclike bodies with only one opening and tentacles with stinging structures.

Tutor's tip: This word was used in the 2006 Scripps National Spelling Bee finals.

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For a list of words related to cnidarian, see:

Mollusks and aquatic invertebrates - cnidarian: formerly coelenterate; member of a phylum of invertebrates having a single, internal digestive cavity with tentacles on the oral end, a primitive nervous system, and special protective stinger cells, including jellyfish, sea anemones, and coral

Related topics:

	craspedon (invertebrate zoology)
	Heterophyllidae (paleontology)
	gonopalpon (invertebrate zoology)

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