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Cnidaria
Cnidaria or Coelenterata , phylum of invertebrate animals comprising the sea anemones , corals , jellyfish , and hydroids. Cnidarians are radially symmetrical (see symmetry, biological ). The mouth, located at the center of one end of the body, opens into a gastrovascular cavity, which is us...
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Coelenterata
Coelenterata , another name for the phylum Cnidaria .
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sea fan
sea fan colonial marine animal forming erect, flattened, branching colonies in tropical and subtropical waters. Colonies may be several feet high and are often colorful, with purples, reds, and yellows predominating. The individuals, or polyps (see polyp and medusa ), have eight feathery tentacles...
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hydra
hydra , common name for freshwater organisms in the phylum Cnidaria, which includes jellyfish, sea anemones, and corals. Hydras are widely distributed in lakes, ponds, and sluggish streams. They are small, cylindrical, solitary organisms, the largest reaching about 1 in. (2.5 cm) in length. They att...
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invertebrate
invertebrate , any animal lacking a backbone. The invertebrates include the tunicates and lancelets of phylum Chordata, as well as all animal phyla other than Chordata. The major invertebrate phyla include: the sponges ( Porifera ), coelenterates ( Cnidaria ), echinoderms ( Echinodermata ), flat...
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sea pen
sea pen long, slender colonial organism of the same phylum as the jellyfish. Sea pen colonies are formed by several genera of the order Pennatulacea. The colony consists of a stalk formed by an organism called a primary polyp (see polyp and medusa ) and short branches formed by secondary polyps. T...
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sea anemone
sea anemone , any of the relatively large, predominantly solitary polyps (see polyp and medusa ) of the class Anthozoa, phylum Cnidaria. Unlike the closely related corals, these organisms do not have a skeleton. Sea anemones occur everywhere in the oceans, at all depths, but are particularly abunda...
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ectoderm
ectoderm layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endoderm , or inner layer, is present in all early embryos. In the development of animals of the phyla Porifera , Ctenophora , and Cnidaria , t...
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jellyfish
jellyfish common name for the free-swimming stage (see polyp and medusa ), of certain invertebrate animals of the phylum Cnidaria (the coelenterates). The body of a jellyfish is shaped like a bell or umbrella, with a clear, jellylike material filling most of the space between the upper and lower...
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Ctenophora
Ctenophora , a small phylum of exclusively marine, invertebrate animals, commonly known as sea walnuts or comb jellies. Because they are so delicate that specimens are difficult to collect, little was known about them until the advent of blue-water scuba and submersible collecting. Ctenophores are c...
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