ABYSSAL BENTHAL AND PELAGIAL 



253 



on hooks at depths of 360 m. by day feed on cephalopods {Ominas- 

 trephes) which are taken at the surface at night. Smaller animals also 

 make these periodic ascents and descents. The details have been 

 ascertained for Calanus fimnarchicus? During the day, from 6 a.m. 

 to 6 p.m., it is taken at 350- to 450-m. depth; from 6 to 8 p.m. it is 

 uniformly distributed from 350 m. to the surface; about midnight the 

 whole population accumulates between 46 and 3 m., and between 4 and 

 6 a.m. the majority are at a depth of 180 m. The composition of the 

 surface plankton in consequence varies from night to day. Animals of 



Fig. 66. — Deep-sea crab, Platymaia wyville-thomsoni from 275-800 m., one-third 



natural size. After Doflein. 



deep water may come to the surface for egg-laying. Nautilus, an 

 archaic cephalopod, an inhabitant of great deeps, comes to the shallow 

 water near Amboina from May to September for this purpose. 10 



Abyssal characters common to pelagial and benthal. — In spite 

 of the interdigitation of the deep-sea fauna with that of the lighted 

 zone, the peculiarities of the environment to which all deep-sea crea- 

 tures are subject result in many adaptations which produce similar 

 bodily characteristics. The peculiarities consist in the food, the absence 

 of light, the stillness of the water, the low temperature, and the great 

 pressure, the uniformity of these factors being more marked than in 

 the rest of the ocean. 



Living plants are not available to deep-sea animals as food. The 

 food of the deep-sea forms, except as they prey upon each other, is 



