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.
Class HYDROZOA
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.
Class SCYPHOZOA
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.
Class CUBOZOA
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.