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Terms in this set (497)

-A group of organisms with radial symmetry
-Two body structure (polyp and medusa)
-Have a nerve net and stinging cells in their tentacles
-Phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments.
-Their distinguishing feature are cnidocytes, a type of venomous cell used mainly for capturing prey.
-Contain only 2 layers of cells (endoderm and ectoderm). Includes jelly fish and hydra.
- diploblastic; two layers of cells — ectoderm and endoderm — with a jellylike mesoglea between them;
-predominantly radial symmetry: body parts (e.g., tentacles) arranged in whorls. However, in some sea anemones, there is only one plane through the tubular body that divides it into two mirror-image halves; thus revealing bilateral symmetry.
- cnidoblasts: specialized cells that secrete a stinging
capsule called a nematocyst.
-Food is taken through a mouth into the gastrovascular cavity. The cavity is also called a coelenteron and for many years the name of this phylum was Coelenterata. There is no anus.
-The phylum contains about 10,000 species distributed in 3 classes:
* Hydrozoa Although the freshwater hydra is a much-studied representative, it is not typical of the class.
Most members are
- marine
- colonial
- produce two body forms: the sessile polyp (like the hydra) and the free-floating medusa (which disperses the species)
* Scyphozoa Jellyfishes (the medusa stage is dominant). The jelly of the medusa is a much-enlarged mesoglea.
* Anthozoa Sea anemones and corals. Have only the polyp stage.