CHAPTER VI 



PHYLUM CTENOPHORA 



THE Phylum CTENOPHORA (Gr. ktenos, of a comb; phoreo, 

 I bear) includes a small group of free-swimming marine animals 

 which are even more nearly transparent than the ccelenterate 

 jellyfishes. They have been placed by many authors under 

 the Phylum CCELENTERATA, but the present 

 tendency is to separate them from that 

 group and rank them as a distinct phylum 

 (p. 25). They are widely distributed, being 

 especially abundant in warm seas. 



Ctenophores are commonly called sea 

 walnuts because of their shape (Fig. 92), or 

 comb jellies on account of their jelly-like 

 consistency and the comb-like locomotor 

 organs arranged in eight rows on the sides 

 of the body (Fig. 93, A, 5; Fig. 93, B, ctr). 

 A few species have a slender ribbon-like (From Weysse, after 

 shape and may, like Venus' girdle (Fig. 94), A 8 assiz ^ . excretory 



. & . pore; b, paragastnc 



reach a length of from six inches to four aan al ; c, circular 



fggt canal ; d-h, ciliated 



bands. (From Weysse, 



The general structure of a ctenophore is after Agassiz.) 

 shown in Figure 93. It is said to possess 

 biradial symmetry, since the parts, though in general radially 

 disposed, lie half on one side and half on the other side of a 

 median longitudinal plane. An end view, as in Figure 93, B, 

 illustrates this fact. The mouth (Fig. 93, A, i) is situated at 

 one end (oral) and a sense-organ (Fig. 93, A, 2) at the opposite 

 or aboral end. Extending from near the oral surface to near 

 L 145 



FIG. 92. A cteno- 

 phore, Idyia roseola. 



