ANTHOZOA. 29 



Class II. Anthozoa (Actinozoa). Corals. 



Polypes with gullet (stomodseum), which, is fixed to the body- wall by 

 mesenteries, which bear mesenteric filaments and the endodermal genital 

 glands. Sexes generally separated. A crown of hollow tentacles sur- 

 rounds the elongated mouth. Usually with a firm calcareous non- 

 superficial skeleton, and frequently colonial by budding. For the most 

 part inhabitants of shallow water (coral reefs). 



Order 1. Rugosa (Tetracoralla). Palaeozoic (except Holocystis) corals, 

 with numerous tetramerously grouped septa. Cyathophyllum. 



Order 2. Alcyonaria (Octactinia, Octocoralla), with eight pinnate 

 tentacles, and as many uncalcified mesenteric folds with ventral retractor 

 muscles. Calcareous spicules usually present in the mesoglcea. 

 Alcyonium digitatum, dead man's fingers, stocks of fleshy polypes. 

 Pennatula rubra and Veretillum, sea-pens, stocks, of which the naked 

 basis sticks in the mud, horny axial skeleton ; the latter dioecious. 

 Gorgonia ; Corallium rubrum, red coral. Tubipora purpurea, organ- 

 pipe coral. Heliopora, massive skeleton, dimorphic polypes. ,: 



Order 3. Zoantharia (Hexactinia, Hexacoralla). The number of the 

 non-pinnate tentacles, and mesenteric pouches, six, or a multiple thereof. 

 Mesenteries usually paired, and the retractor muscles not arranged as 

 in Alcyonaria. Generally a compact skeleton. Actinia mesembry- 

 anthemum, sea anemone, a solitary form with several alternating circlets 

 of tentacles ; fixed by an adhesive disc ; Cerianthus, elongated with an 

 aboral pore ; hermaphrodite. Antipathes, with six tentacles and a 

 horny skeletal axis. 



We group together as Madreporaria the forms with a firm cal- 

 careous skeleton. Aporosa : Caryophyllaea. Oculina virginea. 

 Astrsea. Maeandrina, brain coral. Fungia discus, mushroom coral. 

 Perforata : Madrepora cervicornis. Asteroides. 



