86 



THE MOST PRIMITIVE METAZOA 



Fig. 29. Ctenophora. A typical ctenophoran such as Pleurobrachia 

 shown here is a round transparent animal with eight ciliated comb 



rows. (From Hyman.) 



suggested that the nematocysts were formed mainly during the 

 larval phase of the ctenophore. The nematocysts differ in 

 structure from those of the narcomedusae, which would indicate 

 that they cannot be derived from Cunina. Furthermore all the 

 specimens had nematocysts. 



All these points lead one to conclude that Euchlora has its own 

 true nematocysts. This would then indicate that the ctenophores, 

 or at least this ctenophoran, belong to the Cnidaria ! 



The apparent wide embryological differences between the 

 coelenterates and the ctenophores may be diminished when we 

 know more about the range of embryological development of the 



