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coelom

(Encyclopedia) coelom sē´ləm [key], fluid-filled body cavity, found in animals, which is lined by cells derived from mesoderm tissue in the embryo , and which provides for free, lubricated mo...

mesoderm

(Encyclopedia) mesoderm, in biology, middle layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ba...

pseudocoelomate

(Encyclopedia) pseudocoelomate so͞o˝dōsē´ləmāt˝ [key], any of a group of invertebrates with a three-layered body that has a fluid-filled body cavity (pseudocoelom) between the endoderm and the mesode...

Hertwig, Oscar

(Encyclopedia) Hertwig, Oscar ôs´kär hĕrt´vĭkh [key], 1849–1922, German embryologist. He studied medicine with Haeckel and Gegenbaur. In 1875 he established the fact that fertilization consists of th...

Priapulida

(Encyclopedia) Priapulida, phylum consisting of 17 species of predatory, unsegmented marine worms that live in the sand and mud at the sea bottom. The largest are 4 to 6 in. (10–17 cm) long, but the majorit...

Phoronida

(Encyclopedia) Phoronida fərŏn´ədə [key], small phylum of slender, wormlike marine tube-dwellers, typically found in temperate, shallow seas. About 10 species are known. Although the body is free in the...

Annelida

(Encyclopedia) Annelida ənĕl´ĭdə [key] [Lat., anellus =a ring], phylum of soft-bodied, bilaterally symmetrical (see symmetry, biological ), segmented animals, known as the segmented, or anne...

embryo

(Encyclopedia) embryo ĕm´brēō [key], name for the developing young of an animal or plant. In its widest definition, the embryo is the young from the moment of fertilization until it has become str...

Arthropoda

(Encyclopedia) Arthropoda ärthrŏp´ədə [key] [Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans , insects , centipedes , millipedes , ...

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