42 COELENTERATA 



Order 1. Stauromedusae. 



Conical or vase-shaped umbrella. No ten- 

 taculocysts. (Lucernaria, Tessera.) 



Order 2. Peromedusae. 



Conical umbrella with transverse constriction. 

 Four interradial tentaculocysts. (Pericolpa.) 



Order 3. Cubomedusae. 



Four-sided umbrella. With perradial tentacu- 

 locysts. Velum present. (Charybdea.) 



Order 4. Discomedusae. 



Saucer-shaped umbrella. Perradial and inter- 

 radial tentaculocysts. (Aurelia, Cyanea.) 



Class 3. Actinozoa. 



With a stomodaeum, and with mesenteries ex- 

 tending into the coelenteron. Fixed forms. 



Subclass 1. Zoantharia. 



Mesenteries and tentacles usually very numer- 

 ous. 



Order 1. Actiniaria. 



Usually single. No skeleton. (Metridium, Sa- 

 gartia.) 



Order 2. Madreporaria. 



Usually form colonies and always have cal- 

 careous exoskeleton. (Astrangia, Orbicella, 

 Meandrina.) 



Order 3. Antipatharia. 



Treelike. Mesenteries and tentacles compara- 

 tively few. Chitinoid skeleton. (Cirripathes.) 



Subclass 2. Alcyonaria. 



Mesenteries and tentacles eight in number. 

 Tentacles branched. 



Order 1. Alcyonacea. 



Skeleton in the form of small, irregular bodies, 

 frequently calcareous spicules. (Alcyonium, 

 Tubipora.) 



Order 2. Gorgonacea. 



Treelike, with calcareous or horny exoskeleton. 

 No siphonoglyphes. (Gorgonia.) 



Order 3. Pennatulacea. 



Colony with one end usually embedded in the 

 sea bottom. (Pennatula, Renilla.) 



