How Does it Move and Get Food
mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both.
http://en.wikipedia.org/wiki/Cnidaria
http://en.wikipedia.org/wiki/Cnidaria
"Many cnidarians spend their lives attached to objects where they wait for fish or other organisms to swim by them and become trapped by their tentacles. "
http://www.biologycorner.com/worksheets/articles/hydra.html
http://www.biologycorner.com/worksheets/articles/hydra.html