640 



DEPTHS OF THE OCEAN 



largely due to the enormous abundance of this species, which 



constitutes the food of the arctic whales. 

 Vertical In the boreal parts of the Norwegian Sea most of the arctic 



distribution of species occur in the deeper layers in accordance with the hydro- 



Copepocia in ^ , . , ,. , ^1 •' ■, 1 r n • 1 r 



the Norwegian graphical conditious, as shown by the ioUowmg abstract trom a 

 ^^f- table given by Damas and Koefoed : — 



According to this table a peculiar bathypelagic fauna appears 

 to exist in the Norwegian Sea, whether the surface layers be 

 warm or cold. We find, however, many transitions between 

 the typically arctic and the typically boreal forms, and the 

 most intimate knowledge of their distribution and life-history 

 is necessary to enable us fully to characterise the various 

 species. 



Among the pteropoda Limacina helicina is typically arctic ; 

 it spawns on the coast banks of Greenland at a temperature of 

 0° C, and between the ice-floes, the young being gradually 

 distributed into deeper water. 



As already indicated, there are certain medusae which must 

 be considered as arctic coast forms (see Fig. 398, p. 570), such 

 as Hippocrene superciliaris, Codonium princeps, Catablevia 

 campanula. Of oceanic medusae Aglantha digitalis is found 

 in the upper layers, and Crossota norvegica in the deepest layers 

 of the Norwegian Sea, both being characteristic forms. 



The siphonophore Diphyes arctica, the sagittidae Krohnia 

 kamata, Sagitta gigantea and S. arctica, the ostracod Conchcecia 

 borealis, the schizopoda Meganyctiphanes norvegica, Boreophausia 

 inennis and Thysanocssa longicaitdata, the amphipoda Euthetnisto 



