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Hydrozoa

Hydrozoa (hydroids; phylum Cnidaria) A class of multicellular, mainly marine animals in which the cells are derived from two layers, epidermis and gastrodermis (endodermis), separated by a gelatinous mesogloea. These enclose a continuous gastrovascular cavity (coelenteron), which communicates directly with the exterior by a single aperture (mouth) and is lined by a gastrodermis. The gastrodermis lacks nematocysts. Eggs and sperm are shed outside the animal and not into the gastrovascular cavity.

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Hydrozoa

Hydrozoa (hydroids; phylum Cnidaria) Class of multicellular, mainly marine animals with cells arranged in two layers, the epidermis and the gastrodermis (endodermis), separated by a gelatinous mesogloea. These enclose a continuous digestive cavity (coelenteron), which communicates directly with the exterior by a single aperture (mouth) and is lined by a gastrodermis. The gastrodermis lacks nematocysts. Hydrozoa are Lower Cambrian to Recent. See also MILLEPORINA; and STYLASTERINA.

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hydrozoa

hydrozoa Class of animals without backbones, all living in water, belonging to the phylum Coelenterata. They vary in shape and size from the large Portuguese man-of-war to the simple hydra.

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Hydrozoa

Hydrozoa See Cnidaria.

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