PELAGIC ANIMAL LIFE 



567 



large forms, of which the 

 species P. naresi is the 

 largest. These forms have 

 been taken in abundance only 

 at the greatest depths, as is 

 the case with the giant race 

 of A ulacantha scolyinantJia. 

 Among Norwegian Sea forms 

 we may mention Protocystis 

 bicof'nis and P. harstoni, Chal- 

 lengeria xipliodon^ and Poros- 

 pathis Jiolostoma, the three 

 latter being found in the 

 Atlantic as well. P. holostoina 

 has been taken at great depths 

 in the Norwegian Sea and in 

 the Sargasso Sea. 



The Tuscaroridae are 

 genuine deep-sea forms, 

 having a bottle - shaped shell 

 provided with large strong 

 spikes arranged in rings 

 around the main axis (see 



Fi! 



195). 



In hauls with 



closing nets they have never 

 been taken in less than 400 

 metres of water ; some species, 

 for instance Tiiscaretta tubulosa, 

 occur in all oceans. 



Remarkable deep - sea 

 forms, as well as certain 

 small surface forms, belong 

 to the Medusettidae. Medu- 

 s etta arc ife ra has been 

 taken in the Norwegian 

 fjords. 



On the basis of his 

 study of the Radiolarians of 

 the " Valdivia " Expedition, 

 Haecker distinguishes the 

 following bathymetrical 

 regions : — 





IW 



(i) An upper Acanthometra- 

 layer. 



(2) A Challengeria-layer (50 to 



400 metres). Fig. 394. 



(3) A Pandora - layer (from Challengeridas (-f). i, Protocystis swirei, John 

 A i/lographis pandora, 400 to 1000 Murray; 2 and 3, Protocystis tridens, Haeckel ; 



metres), in which the Tuscaroridse 

 are also found. 



Protocystis ihomsoni, John Murray. 

 Haecker. ) 



(From 



