Coelenterates are radially symmetrical, diploblastic aquatic animals with diffused nervous system. Stinging cells or nematocysts are present for defense. Digestive system is in a blind sac plan, with mouth as the only opening. Life cycle shows a kind of alternation of generations called metagenesis.
Solitary or colonial, with polyp as the dominant stage. Mesogloea is acellular. Cnidocytes are confined to epidermis. Gonads are epidermal. Ex. Hydra; Bougainvillea; Obelia; Millepora; Stylaster; Physalia; Vellela; Porpita.
Solitary marine animals, with medusa as dominant stage and without a velum. Mesogloea is highly enlarged with cells. Reproductive organs are gastrodermal. Sense organs are located on the bell margin. Ex. Aurelia; Pelagia; Cyanea.
Similar to Scyphozoa but smaller and having strong nematocysts. Commonly known as sea wasps. Quadriradial symmetry, with 4-sided bell and having 4 bunches of tentacles. Oral arms absent. Ex. Chironex; Tripedalia; Tamoya; Carybdea.
Class ANTHOZOA (=ACTINOZOA)
They occur only in polyp form. Medusa form is absent. Pharynx present with two ciliated grooves called siphonoglyphs. Mesogloea is cellular and gonads gastrodermal.
Subclass OCTOCORALLIA (=ALCYONARIA)
Polyp with 8 tentacles and 8 septa. Colonial forms only. Ex. Tubipora; Alcyonium; Heliopora; Gorgonia; Corallium; Pennatula; Renilla.
Subclass HEXACORALLIA (=ZOANTHARIA)
Solitary or colonial; polyp with 6 or multiple of 6 tentacles. Ex. Zoanthus; Metridium; Adamsia; Antipathes; Fungia; Astraea; Madrepora; Meandrina.