CHAPTER IV 



Sea walnut and Venus' girdle 



The Comb Jellies 



{Pliyhini CtcuopJwra) 



o 



N a smooth stretch of wave-washed sandy 

 beach one's attention is easily caught, even at some 

 distance, by little oval balls of clear jelly that glisten 

 in the sun like crystal beads. "Cat's eyes," fishermen 

 on the American Pacific coast call them, and on 

 many other shores such stranded comb jellies are 

 known as "sea gooseberries" or, in the case of some 

 of the slightly larger species, as "sea walnuts." If 

 they are not too far gone the Httle sea gooseberries 

 will revive in sea water, regain their gossamer loveli- 

 ness, and swim about like paddle boats, propelled 

 by the rapid beating of eight vertical rows of ciliary 

 combs that radiate over the rounded body like the 

 lines of longitude on a globe. The delicate trans- 

 parency of comb jellies makes them all but invisible 

 in the water, so that often they reveal themselves 

 only in the rippling iridescence of the rows of beating 

 combs as they difi'ract the light. Unless the water is 

 smooth as glass they are likely to remain below the 

 surface, and even when they come within one's 

 reach they slip between the fingers or tear to shreds 

 at the touch of an oar. Such diaphanous creatures 

 are best gathered by towing a net behind a boat, but 

 a few may be dipped up in a small net or container. 

 The daytime play of rainbow colors is replaced at 

 night by luminescent waves of an intensity that is 

 matched only by some of the deep-sea fishes. On 

 summer nights the waters beneath a jutting wharf 

 may shine with hundreds of languidly gliding 

 comb jellies, which at the slightest disturbance light 

 up along the eight comb rows. Dipped up and taken 

 in a jar of sea water to a lighted room, they cease to 



glow. Then, if the room is darkened for at least 

 twenty minutes, they shine again with a bluish or 

 greenish light. 



The phylum name, Ctenophora, means "comb- 

 bearers," and the swimming paddles are made of 

 large cilia that are fused at the attached end like the 

 teeth of a comb. They are regulated and coordi- 

 nated in their movements by a network of nerve cells 

 that connect with a tiny sense organ housed in a 

 glassy little dome atop the upper pole, the one oppo- 

 site the mouth. Presumably the sense organ is con- 

 cerned with balancing and helps to orient the ani- 

 mal as it swims. 



The more primitive comb jellies, like the little sea 

 gooseberries, have two long tentacles with which they 

 fish for food. At times these are drawn up into 

 knotted, stringlike masses, at other times stretched 

 far out in graceful sweeping curves, the side 

 branches that fringe one edge lending a plumelike 

 elegance. The more advanced groups of comb jellies 

 have only fringes of short tentacles or lack them al- 

 together. When present, the tentacles or their side 

 branches are thickly studded with special adhesive 

 cells, unique to ctenophores and not to be confused 

 with the thread capsules of coelenterates. The pro- 

 truding heads of the adhesive cells are very sticky 

 and cling to prey. At their inner ends they are at- 

 tached to spirally coiled contractile filaments that 

 yield to the pull of struggling prey but cannot be 

 wrenched loose. 



This is an exclusively marine group, though some 

 do flourish in bays and estuaries with a salt content 



[115 



