A class of Cælenterata; radiated, marine zoöphytes, embracing the sea-anemones, corals, sea-pens, etc., in which the mouth is furnished with hollow retractile tentacles, simple in one subclass (Zoantharia) or fringed in the other (Alcyonaria).
the GNU version of the Collaborative International Dictionary of English
noun plural.
A group of Cœlenterata, comprising the Anthozoa and Ctenophora. The sea anemone, or actinia, is a familiar example.