cnidaria - Phylum Cnidaria - Jellyfish - about 9,000...

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Phylum Cnidaria - Jellyfish - about 9,000 species, all aquatic, and mostly marine. - radial symmetry, acoelomate (remember - a gastrovascular cavity is NOT a body cavity). - basically consist of a sac, which forms a gastrovascular cavity (gut) which is surrounded by tentacles at the opening to the outside (easy to see how one can get from a “gastrula” to a Cnidarian). - there is only one opening, so this functions as mouth and anus. Prey is caught with the tentacles, moved into the gut, digested, and then the remains are expelled. - two main forms [Fig. 33.5, p. 671] : polyps - animal is usually anchored in one place, and the opening is on the opposite side of the anchor (i.e., it usually points up). medusa - animal floats (can move actively), opening usually points down (sort of like a bell). many species go through both forms during their life cycle, but one form usually predominates. Basic body plan: have two layers, an ectoderm and an endoderm. This usually surrounds what is known as the mesoglea. Mesoglea - a middle layer of gelatinous (i.e. the “jelly”) material.
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This note was uploaded on 04/29/2009 for the course BIOL 303 taught by Professor Birchard during the Spring '08 term at George Mason.

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cnidaria - Phylum Cnidaria - Jellyfish - about 9,000...

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