266 MARINE ANIMALS 



Although most species of the deep-sea fish Cyclathone are subtropical, 

 C. livida occurs only on the West African coast, where it is abundant. 



Local specialization accordingly takes place also in the deep sea. 

 Such differentiation is further increased where there are great barriers 

 which are insurmountable for many animals. The Faeroe Ridge between 

 the Norwegian Sea and the Atlantic, and its continuation in the direc- 

 tion of the northeast corner of Scotland, the Wyville-Thomson Ridge, 

 is such a barrier. The effect of the latter is the more notable as it ex- 

 tends as a narrow ridge, whose deepest point is 556 m. below the 

 surface, between depths of more than 1000 m. on each side. North of 

 this ridge the temperature drops much faster with depth than it does 

 to the south (Fig. 14) so that in the Faeroe-Shetland channel, at depths 

 of 1100 m., a temperature of +0.41° prevails, and scarcely a degree 

 farther to the south, at an equal depth, the temperature is +8.07°. At 

 the deepest point on the ridge, the temperature is +7.5°, so that for 

 stenothermal cold-water forms this ridge is an impassable barrier. 

 This barrier shuts out the whole of the Atlantic deep-sea fauna from 

 the Norwegian Sea ; the only exchange of forms possible is in the upper- 

 most zone. Murray lecords 385 species of animals from both sides of 

 the barrier, of which only 48 (12%) are common to both the warmer 

 Atlantic and the colder Norwegian Sea. No Atlantic abyssal species of 

 fish are found in the northern ocean. The genera Cyclothone and 

 Macrurus, which play an important role in the Atlantic, are wholly 

 wanting, while in the Norwegian Sea Lycodes (related to the "eel 

 mother" Zoarces) predominates, with only a few special forms in the 

 Atlantic. Just south of the ridge animals are found which range to the 

 Canary Islands; a few kilometers to the north forms occur which 

 extend to Spitzbergen and even farther. 33 Similar differences are also 

 shown in the benthic fauna of the two sides of the ridge. 



Abyssal animals reviewed. — Although a considerable number of 

 the deep-sea animals are eurybathic and range upward into the lighted 

 zone, and although the peculiar adaptations to the deep-sea environ- 

 ment are by no means general, so that a special character of deep-sea 

 life can be asserted only with reservations, the composition of the deep- 

 sea community, according to the groups of animals represented, is so 

 different from that of the lighted zones in the ocean that there is a 

 recognizable peculiarity in this respect. A rapid review of the deep-sea 

 fauna shows this plainly. Among the radiolarians, Nasselaria and 

 Phaeodaria outnumber the Spumelaria and Acantharia with increasing 

 depth, and the family Challengeridae is confined to the abyssal pela- 

 gial. Foraminifera are abundant in the abyssal benthal, especially 

 imperforate forms with sandy shell. The Globigerina ooze is composed 



