One of a large class of sedentary marine coelenterates in which the medusoid phase is entirely suppressed: The actinozoa include the sea anemones, sea-pens, and corals.

"Coelenterates" are invertebrate animals that include the hydras, jellyfishes, sea anemones, and corals, all of which are characterized by a single internal cavity serving for digestion, excretion, and other functions and having tentacles on the oral (mouth) end.

"Medusoid" refers to the tentacled, usually bell-shaped, free-swimming sexual stage in the life cycle of a coelenterate, such as a jellyfish.