COELENTERATA. 



With a single continuous coelenteron or gastro-vascular cav- 

 ity. With the exception of the Ctenophora all have nettle cells. 

 There are two cellular layers and a mesoglea. 



Class 1. Hydrozoa. 



Coelenteron simple, without septa. Gonads usu- 

 ally ectodermal. Fully formed medusae have a 

 velum. 

 Order 1. Leptolinse. 



With a fixed zooph3^te stage. 

 Suborder 1. Anthomeclusse. 



Without hydrothecse or gonothecse. The medusa 

 bears gonads on the manubrium. (Hydra, Pary- 

 pha.) 

 Suborder 2. Leptomedusse. 



With hydrothecffi and gonothecae. The medusa 

 bears gonads on the radial canal. (Obelia, Goni- 

 onemus.) 

 Order 2. Trachylinae. 



Without fixed zoophyte stage. 

 Suborder 1. Trachymedusae. 



Tentacles from the margin of the umbrella. 

 Gonads on the radial canals. (Petasus.) 

 Suborder 2. Narcomedusae. 



Tentacles from the exumbrella. Gonads on the 

 manubrium. (^Eginopsis.) 

 Order 3. Hydrocorallina. 



Massive calcareous exoskeleton. (j\Iillepora.) 

 Order 4. Siphonophora. 



Pelagic. Colonial. Colony usuall}^ shows extreme 

 polymorphism of its zooids. (Physalia.) 

 Class 2. Scyphozoa. 



Body-wall of polyp thrown into four ridges (taeni- 

 oles) which project into the coelenteron. Medusae 

 without velum and with gastric tentacles. 

 Medusoid form predominating. 

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