cni·dar·i·an 
(nī-dârē-ən)
(nī-dârē-ən)n.
Any of various invertebrate animals of the phylum Cnidaria, characterized by a radially symmetrical body with a saclike internal cavity and stinging nematocysts, and including the jellyfishes, hydras, sea anemones, and corals.
[New Latin Cnīdāria, phylum name, from Greek knīdē, sea nettle.]
cni·dari·an adj.