From Openwaterpedia

noun - Cnidarian is any invertebrate animal, as a hydra, jellyfish, sea anemone, or coral, considered as belonging to the phylum Cnidaria, characterized by the specialized stinging structures in the tentacles surrounding the mouth.

adjective - Cnidarian belongs or pertains to the Cnidaria.

[Origin: from New Latin Cnidaria, from Greek knidē nettle]