PELAGIC ZONE SURFACE LIFE 



453 



of these curious Worms, like those of the last-named group, are 

 well represented in the surface waters of the sea, and some adult 

 Nemertines have given up creeping and taken to a pelagic life. 



One of the most remarkable (Pela- 



gonemertes) is represented in fig. 



1308. 



Plankton Thread-Worms (Ne- 



mathelmid). - - Among the 



corn- 



Fig. 1308. Pelagic Nemertine Worm 

 (Pelagonemertes], reduced 



Fig. 1309. Night-Light Animalcules 

 (Noctiluca], enlarged 



monest inhabitants of the surface waters are the curious little 

 fish-shaped Arrow -Worms (Sagitta, Spade lla, &c.), which con- 

 stitute a special group (Chatognatha) that is generally supposed 

 to be an outlying constituency of the Thread-Worms (see vol. iii, 

 p. 2 1 ), though its affinities are doubtful. 



Fig. 1310. Shells of Ray-Animalcules (Radzolatia], imbedded in the 

 fibrous skeleton of a sponge 



Plankton Zoophytes (Ccelenterata}. A bewildering variety of 

 jelly-fishes, belonging to all sorts of groups, abound in the surface 

 waters. Many of them have abandoned altogether the fixed 

 zoophyte-stage that is found in the life-history of many such 

 creatures (see vol. iii, p. 349). Perhaps the most interesting 



VOL. IV. 



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