Cnidaria (silent c - pronounced // from New Latin cnida, fr. Gk κνιδη "nettle") is a phylum containing some 11000 species of relatively simple animals found exclusively in aquatic, mostly marine, environments. Cnidarians get their name from cnidocytes, which are specialized cells that carry stinging organelles. The corals, which are important reef-builders, belong here, as do the familiar sea anemones, jellyfish, sea pens, sea pansies and sea wasps. The names Coelenterata and Coelentera were formerly applied to the group, but as those names included the Ctenophores (comb jellies), they have been abandoned. Cnidarians are highly evident in the fossil records, having first appeared in the Precambrian era.

The basic body shape of a cnidarian consists of a sac with a gastrovascular cavity, with a single opening that functions as both mouth and anus. It has radial symmetry, meaning that whichever way it is cut along its central axis, the resulting halves would always be mirror images of each other. Their movement is coordinated by a decentralized nerve net and simple receptors. Several free-swimming Cubozoa and Scyphozoa possess rhopalia, complex sensory structures that can include image-forming eyes with lenses and retinas ^*, and a gravity-sensing statolith comparable in function to the otolith of the vertebrate inner ear. Tentacles surrounding the mouth contain nematocysts, specialized stinging cells, which they use to catch prey and defend themselves from predators. The ability to sting is what gives cnidarians their name.

There are four main classes of Cnidaria:

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Acanthocephala, Acoelomorpha, Annelida, Arthropoda, Brachiopoda, Bryozoa, Chaetognatha, Chordata, Cnidaria, Ctenophora, Cycliophora...
pippppo (Philippe Araujo) Sat, 12 Dec 2009 01:54:42 -0000
Acanthocephala, Acoelomorpha, Annelida, Arthropoda, Brachiopoda, Bryozoa, Chaetognatha, Chordata, Cnidaria, Ctenophora, Cycliophora...
@edyong209 yeah, bloody taxonomist show offs. Phyla with only 1 member should be made to squeeze in somewhere else. Cnidaria maybe.
AdamRutherford (Adam Rutherford) Wed, 09 Dec 2009 21:12:02 -0000
@edyong209 yeah, bloody taxonomist show offs. Phyla with only 1 member should be made to squeeze in somewhere else. Cnidaria maybe.
Just hit the four page mark on my paper about Cnidaria. Woo hoo! I can stop at any time!
jessicayaq (Jessica Yaquiant) Wed, 09 Dec 2009 17:50:05 -0000
Just hit the four page mark on my paper about Cnidaria. Woo hoo! I can stop at any time!
Phylum: porifera, cnidaria, nematoda, anthropoda, annelidia, echinodermata, platyhelminthes, chordata, mollusca <-- sigh.
veeronicaa (veronica deguzman) Wed, 09 Dec 2009 07:47:25 -0000
Phylum: porifera, cnidaria, nematoda, anthropoda, annelidia, echinodermata, platyhelminthes, chordata, mollusca <-- sigh.

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