262 MARINE ANIMALS 



snail Glaucus (Fig. 53a). The dorsal half of pelagic juvenile fishes 

 (Mullus) , and of adult fishes like sardines, mackerels, and the flying 

 fishes, is blue. The dark brown back of the herring is invisible from 

 the surface, and only the silvery gleams from their sides make them 

 visible. In the lower stages of the lighted zone, with dim light, the 

 fishes are predominantly silvery. 



In greater depths, where light is absent, and where a uniform ooze 

 covers the bottom, colorations are much more uniform. There is a 

 decided predominance of red colorations in all tones, besides dark 

 brown, dark violet, and black. The absence of red light in depths even 

 of 50 m. makes red appear as black, as shown by Fol in diving experi- 

 ments in the Mediterranean. Some Foraminifera of the deep sea are 

 striking for their dark reddish violet and black coloration. In the 

 abyssal benthal are red hydroid polyps, such as the gigantic Branchio- 

 cerianthus imperator, bright red sea anemones, and intensely red 

 alcyonarians, in contrast with the yellow, green, and brown forms of 

 the littoral. 20 The starfish of the deep sea are red, orange, or terra 

 cotta in color. Red cephalopods are not rare, and red crustaceans are 

 abundant. The shells of snails and lamellibranchs, however, are mostly 

 colorless, or with pale coloration. The same colorations are found in 

 the lightless pelagial. The scyphomedusan Atolla has increasingly dark 

 coloration with depth, in contrast with its glass-like relatives of the 

 surface. The bathypelagic larvae of Velella are red. The deep-sea 

 nemertean (Pelagonemertes) , some arrowworms, and a number of 

 pelagic cephalopods are red; the deep-sea pelagic holothurian Pelago- 

 thuria (Fig. 57) is deep rose. Many deep-sea copepods are dark violet. 

 Almost all decapod crustaceans below 750 m. in the tropics, 500 m. in 

 the temperate zones, and 200 m. in polar seas are uniformly red. The 

 abyssal fishes are mostly dark violet or black, and red is a rare color 

 among them. Cyclothone microdon, from deep water, is black, while 

 C. signata, whose lower limit coincides with the upward range of the 

 former species, is light-colored. There are also, to be sure, colorless 

 animals in the abyssal pelagial such as the crustacean Sergestes mag- 

 nificus, the annelid Tomopteris (Fig. 53c), and the fish Bathypterois 

 longicauda (Fig. 72). 



Body form and skeleton. — In depths below 100 m. the water has 

 little motion. This makes possible structural forms which are impossible 

 in moving water. Delicate, slender, long-stalked animals, or forms with 

 an ungainly walk on stilt-like legs, are not uncommon. The wonderfully 

 fragile glass sponges (Hexactinellidae) , the long-stemmed crinoids, and 

 long-legged crabs like Kaempfferia require motionless water. Fishes 

 with tails drawn out into long points, such as Chimaera (Fig. 73), the 



