It is a phylum containing over 9,000 species found only in aquatic and mostly marine environments.
Cnidaria. Cnidaria is a phylum containing over 9,000 species found only in aquatic and mostly marine environments. All cnidarians have radial symmetrical. There are two major body forms among the Cnidaria-the polyp and the medusa. Sea anemones and corals have the polyp form, while jellyfish are typical medusae. When you look at them, you can see that these body forms are the same except that one is upside down. Box Jellyfish. Phylum Cnidaria. Cnidaria is a large phylum composed of some of the most beautiful of all the salt and freshwater organisms: the true jellyfish, box jellyfish, coral and sea anemones, and hydra. Although Cnidaria is an incredibly diverse group of animals, there are several traits that link them together.  Cnidaria is one of the more primitive animal phyla. It includes aquatic organisms such as jellyfish, sea anemones, corals, and hydras. Most cnidarians are marine, although a few, such as the well-known hydra, are freshwater species. Cnidaria A phylum that comprises the sea anemones, jellyfish, and corals, and which is known from the late Precambrian. Cnidarians are basically radially symmetrical and have tentacles. The body contains a gastrovascular cavity and the body wall is diploblastic. In some species, cnidocytes can also be used as anchors. Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians; more complex animals have three main cell layers and no intermediate jelly-like layer. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from endosymbiotic algae, and a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish and turtles. Fossil cnidarians have been found in rocks formed about 580 million years ago, and other fossils show that corals may have been present shortly before 490 million years ago and diversified a few million years later. Fossils of cnidarians that do not build mineralized structures are very rare. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from endosymbiotic algae, and a few are parasites. Many are preyed on by other animals including starfish, sea slugs, fish and turtles. Jellyfish, corals, and other stingers. Cnidarians are incredibly diverse in form, as evidenced by colonial siphonophores, massive medusae and corals, feathery hydroids, and box jellies with complex eyes. Yet, these diverse animals are all armed with stinging cells called nematocysts. Cnidarians are united based on the presumption that their nematocysts have been inherited from a single common ancestor. The name Cnidaria comes from the Greek word cnidos, which means stinging nettle. All jellyfish are Cnidaria, an animal phylum that contains jellies, sea anemones, and corals, among others. There are more than 10,000 species of Cnidaria, and less than 4,000 of these are Medusazoa—those animals we think of as jellyfish. Those 4,000 jellyfish can be divided into four different groups.  What is a Cnidarian? cnidarians, such as jelly fish, sea anemones, hydra, and corals, have tentacles surrounding their mouth. they are a hollow-bodied animal with two celled layers that are organ … ized into tissues. the inner layer forms a digestive cavity where food is broken down. A jelly fish. 1 Animals of the Phylum Cnidaria The phylum Cnidaria includes animals such as corals, jellyfish, and sea anemones. 2  All Cnidarians are aquatic and carnivorous, and they occur in two basic body shapes: polyps,…
http://www.mesa.edu.au/cnidaria/ http://www.angelfire.com/mo2/animals1/phylum/jellyfish.html http://www.encyclopedia.com/topic/Cnidaria.aspx https://en.wikipedia.org/wiki/Cnidaria https://en.wikipedia.org/wiki/Cnidaria http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html http://ocean.si.edu/jellyfish-and-comb-jellies http://www.answers.com/Q/Where_do_Cnidarians_live
where are most cnidarians found