Anus 



Stomach 



COELENTERATA AND CTENOPHORA 

 Sense organ 



Tentacle 



Pharynx 



Mouth 



Fig. 10.17. General structure of a ctenophore; diagrammatic. The characteristic rows of ciliary 

 combs, as well as the external portions of the tentacles, have been omitted. (Redrawn from L. 

 H. Hyman, The Invertebrates: Protozoa through Ctenophora, copyright 1940 by McGraw-Hill Book 

 Co., Inc., printed by permission.) 



the prey until it can be drawn into the mouth. The gastrovascular cavity is 

 divided into pharynx, stomach, and branching diverticula which ramify exten- 

 sively throughout the body. A small anus is present at the aboral end. The 

 resemblances between coelenterates and ctenophores are thus rather super- 

 ficial and are considered insufficient to warrant placing these groups in the 

 same phylum. 



As shown by Figure 10.17, the structure of a ctenophore is rather com- 

 plicated for an animal whose basic organization is so simple. The eight rows 

 of combs, responsible for the name Ctenophora ("comb bearers"), are a unique 

 feature of the phylum. Each row consists of a series of comb-like plates 

 composed of fused cilia; the combs are found in all members of the phylum 

 except a few, where they are lost or modified in the course of development. 

 Locomotion is effected by the beating of the combs, which has been much 

 studied as an example of ciliary action controlled by a nervous system. 

 In addition to a coelenterate-type nerve plexus throughout the body, nervous 

 elements are concentrated beneath the ciliary rows. 



311 



