Actinozo'a

Actinozo'a (Gr. aktis, 'a ray,' and zōon, 'an animal'), one of the three classes of Cœlenterates, including sea-anemones, dead-men's fingers, corals, &c. Like all Cœlenterates, they possess a central mouth and digestive cavity, and are provided with Stinging Cells (q.v.); but they are distinguished from the other two classes (Hydrozoa and Ctenophora) by the possession of a turned-in mouth-tube, forming a stomach region distinct from the body-cavity, and by the presence of a definite number of radial partitions extending from the inner tube to the body-wall. They are provided with tentacles round the mouth, and live either isolated or in colonies. The generative products are always formed on the cross partitions or mesenteries above referred to. The Actinozoa include two orders—Alcyonaria or Octacoralla, with eight tentacles; and Zoantharia or Hexacoralla, with tentacles in sixes. Of the former, Alcyonium, or dead-men's fingers, is a convenient type; and the sea-anemone is a familiar representative of the latter, to which the vast majority of corals also belong. See ALCYONIUM, ANEMONE, CORAL.