CHAPTER XXIX 



PHYLUM CTENOPHORA 



Sfomodeum 



''addle 

 plate 



Tentacle, 



Bearing considerable resemblance to coelenterates because of their 

 jelly-like consistency, the ctenophores are considered by many zoologists 



to be a class of Coelenterata. For 

 reasons which will soon appear, how- 

 ever, it seems more logical to put 

 them in a separate phylum, Cteno- 

 phora (te nof 5 ra; G., ktenos, comb, 

 and phoros, bearing). The cteno- 

 phores are all marine, and the species 

 are relatively few in number. They 

 are widely distributed but are most 

 abundant in the tropics. They are 

 yery transparent and usually delicately 

 tinted with some shade of blue, 

 lavender, or pink. 



182. Structure. — A typical cteno- 

 phore is ellipsoidal or nearly spherical 

 in form and possesses eight rows of 

 paddle plates running from one pole 

 to the other (Fig. 70). Each paddle 

 Paddle plafe plate is a projecting shelf formed by 

 the fusion of the bases of cilia which 

 themselves fringe the margin of the 

 plate. When seen from the side the 

 plates resemble the teeth of a comb, 

 which suggests one common name for 

 this group — comb jellies. Because 



Fig. 70.-A c'tenophore, Pleuro- ^^^^^ ^""^^ ^f paddle pktes form 



brachia bachei A. Agassiz, from Puget TOUghened ridges running from one 

 Sound. A, the organism seen from i . .y^ nthpr sompwhaf rp^pmh- 

 the side. Somewhat diagrammatic. P°^^ ^" ^'^^ °^"^^ SOmewnat reSCmO- 



X i}4- B, diagram of a cross section ling the ridges on a walnut, cteno- 



the*c^anais!°"''* *° '^°'' *^' ''^^*'°''' °^ P^^^^^ ''^^ often Called sea walnuts. 



The mouth is at one pole and leads 

 into a stomodeum, which is connected with a series of canals run- 

 ning through the body. On each side is a sac into which may 



154 



Meridional 

 canal 



Tentacle 



B 



