538 DEPTHS OF THE OCEAN 



Such great temperature differences produce a corresponding 

 dissimilarity in the fauna (see pp. 13 and 661). We have trawled 

 in the cold Norwegian Sea deep basin and captured more or less 

 familiar arctic forms, and then only a few hours steam farther south 

 we have trawled again on the southern slope of the Wyville 

 Thomson Ridge, and taken forms, fishes as well as inverte- 

 brates, which one would expect to find in quite southern areas. 

 Among the deep-water forms of the Atlantic that are 

 present in large quantities on the southern slopes of the ridges 

 and plateaus we have first some species of sea-urchins belonging 

 to the remarkable family of the Echinothuridae (see Fig. 2>77)-^ 

 They differ from all other sea-urchins in the structure of their 

 shells, for, instead of having continuous plates of lime, their plates 

 are connected by non-calcareous attach- 

 ments of skin, so that their shells are 

 flexible and more or less like leather. 

 One species of holothurian, Lcstmogone 

 violacea, is very abundant. It belongs 

 to the same division as the forms Elpidia 

 and Kolga, which are so plentiful in the 

 Norwegian Sea. The " Michael Sars " 

 also found large numbers of the star- 

 fish Zoroaster fic/gens (see Fig. 378). 



The following are a few other 

 forms met with on the southern slopes 

 of the ridges : — 



Regular sea-urchins : Echinus alexandri 

 and E. affinis, Porocidaris purpuvata. Irre- 

 gular sea-urchins : UrecJdmis naresianus, Pourtalesia wandeli, Echinosigra 

 pldale, Hemiaster expergitiis. Starfishes : BatJiybiaster rolmstus (a species 

 which outwardly resembles B. vcxUlifcr of the Norwegian Sea, though 

 the structure of its skeleton is different),- Plutonaster bifrons, Benthopecten 

 spinosus (see Fig. 379), Pentagonaster perrieri, Solaster abyssicola. 

 Ophiurids : Ophiopleura aurantiaca, OpJuomusium lymani, Amphiura 

 denticulata. Coelenterates : EpizoantJius paguripJnhis (in symbiosis with 

 Parapagurus pilosimanus, see Fig. 380), the ^enmXuYids Ant hoptdum mur- 

 rayi and UmbeUula lindaJdi, the true corals StephanotrocJms diadema (see 

 Fig. 381) and Flabelluin sp. (see Fig. 382), the \iOX\\-zox7>\'s, Acanthogorgia 

 annata and Strophogorgia challengeri. Decapod crustaceans : Lispogna- 

 tJms tho7nsoni, ScyramatJna carpenteri^ Geryon affinis, Cymonomus normani, 

 Neolithodes griinaldi, Parapagiirus pdosimanus, Munida microphthalma, 

 Munidopsis curvirostra, Uroptydius rubro-vittatus, Polycheles sculptus and 



Fk;. 380. 

 Epizoanthus paguriphilus, ii 

 osis with Parapagurui 

 manus. Reduced. 

 Sars," 1902, 750 metres 



I symbi- 



pilosi- 



Michael 



^ The species occurring here include Phormosoina placenta, Calveria [Asthenosoma) hystrix, 

 and Sperosoma grinialdii. 



^ According to J. A. (irieg, Conservator of the Bergen Museum. . 



