CCELENTERATA, 



With a single continuous ccelenteron or gastro-vascular cav- 

 ity. With tentacles and nettle cells. With 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. Leptolinae. I 



With a fixed zoophyte stage. 

 Suborder 1. Anthomedusse. 



Without hydrothecae or gonothecse. The medusa 

 bears gonads on the manubrium. (Bougain- 

 villia, Eudendrium, Clava, Hydra, Hydrac- 

 tinia, Pennaria, Tubularia.) 

 Suborder 2. Leptomedusse. 



With hydrothecse and gonothecse. The medusa 

 bears gonads on the radial canal. (Campanu- 

 laria, Gonionemus, Obelia, Sertularia, Tima.) 

 Order 2. Trachylinse. 



Without fixed zoophyte stage. 

 Suborder 1. Trachymedusse. 



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. (^lillepora.) 

 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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