INVERTEBRATE BOTTOM FAUNA 525 



series of species that do not descend to the profound depths. 

 These latter may be designated arctic shallow-water forms, or, Arctic 

 to use a different zoo-geographical description, arctic continental £0^^,^°^"^^^^"^ 

 forms, though it is as well to remember that the depth on the 

 plateaus averages about 400 metres. As in the case of the 

 boreal plateaus, so here, too, we can distinguish between forms 

 that keep entirely to less depths and those which chiefly 

 inhabit the deeper portions. The bottom conditions of the 

 plateaus are quite different from those that prevail in the 

 abyssal region, since hard bottom is to be found as well as soft, 

 whereas the floor of the deep basin consists almost entirely of 

 soft materials ; consequently the plateaus have a far greater 

 abundance of attached animal forms. 



Currents, owing to the increased abundance of nourishment 

 they bring with them, are likewise responsible for the greater 

 profusion of attached forms on the arctic plateaus. To what 

 extent they affect the distribution of animal-life may be seen by 

 comparing the fauna of the west and east coasts of Spitsbergen. 

 Romer and Schaudinn, who made careful researches in 1898, 

 found that on the western side non-attached forms, especially 

 echinoderms, were most in evidence, while on the eastern side, 

 where strong currents flow through the sounds, attached forms 

 predominated. Of this latter area Romer and Schaudinn 

 write as follows : " Most of the rocks and large stones are 

 covered with barnacles, while monascidians and synascidians 

 form populous colonies on the bottom. Sponges, which are 

 scarce on the western side, are represented by numerous 

 species, and alcyonids inhabit the deeper channels. The 

 shallower rocky localities accommodate large congregations of 

 actiniae. The animals, however, which, so to speak, hall-mark 

 the fauna, and are developed in almost fabulous fashion, are 

 hydroids and bryozoa. So dense are the thickets formed in 

 some places by these organisms that the heavy dredge failed 

 to reach the bottom, and merely brought up animals instead of 

 bottom-material." Amongst these attached forms, moreover, 

 there is, just as in the boreal region, a rich fauna of non- 

 attached forms like worms, crustaceans, and molluscs. Romer 

 and Schaudinn drew attention to the fact that the worms, 

 crustaceans, and molluscs, in particular, did not show such a 

 striking difference in their distribution around Spitsbergen as 

 other groups, but were, on the contrary, fairly equally distributed 

 between east and west. Nor are echinoderms absent on the 

 eastern side, where in fact there are actually more species than 



