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. 



Ccelenteron simple, without septa. Gonads usu- 

 ally ectodermal. Fully formed medusae have a 

 velum. 

 Order 1. Leptolinse. 



With a fixed zoophyte stage. 

 Suborder 1. Anthomedusse. 



Without hydrothecse or gonothecse. The medusa 

 bears gonads on the manubrium. (Bougain- 

 villia, Clava, Hydra, Hydractinia, Tubularia.) 

 Suborder 2. Leptomedusse. 



With hydrothecse and gonothecse. The medusa 

 bears gonads on the radial canal. (Campanu- 

 laria, Gonionemus, Obelia, Sertulfiria.) 

 Order 2. Trachylinse. 



Without fixed zoophyte stage. 

 Suborder 1. Trachymedusa?. 



Tentacles from the margin of the umbrella. 

 Gonads on the radial canals. (Petasus.) 

 Suborder 2. Narcomedusse. 



Tentacles from the exumbrella. Gonads on the 

 manubrium. (^Eginopsis.) 

 Order 3. Hydrocorallina. 



Massive calcareous exoskeleton. (Millepora.) 

 Order 4. Siphonophora. 



Pelagic. Colonial. Colony usually shows extreme 

 polymorphism of its zooids. (Physalia.) 

 CLASS 2. Scyphozoa. 



Body-wall of polyp thrown into four ridges 

 (tsenioles) which project into the ccelenteron. 

 Medusa generally without velum and with gas- 

 tric tentacles. Medusoid form predominating. 

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