Re: Cnidarians

Cnidaria [ni-dare-ee-ah] and Coelenterata [so-lent-er-ahh-tah] are just different names for the same phylum. "Cnidaria" refers to the cnidae (threads) found in the stinging cells common to all members of the phylum, while "Coelenterata" refers the coelenteron (internal gut) common to all known members of the phylum. Coelenterata was the original name for the phylum, and has been replaced by Cnidaria, to reflect a more restrictive grouping of these organisms, to exclude genetically unrelated organisms that may have coelenterons but not cnidae.

Admin Note:
You may also want to look into phylum Ctenophora [ten-off-or-ah] which contains the "comb jellies." These organisms resemble jellyfish but have a morphology distinct from true medusae.