500 DEPTHS OF THE OCEAN 



except the sea - anemones already referred to/ which are 

 universally distributed over the central portion of the North 

 Sea, namely dead-men's fingers {Alcyonmin digitatuni) and the 

 sea-pen Virgidaria mirabilis. The former generally consists 

 of irregularly shaped ramifying masses attached by the base to 

 other substances, but in the area examined by the " Michael 

 Sars " during 1904, in depths between 2)^ and 96 metres, 

 temperature 10° to 6.15° C, there was an interesting variation 

 in its relation to its foundation. An annelid [Sabel/a pavonid), 

 commonly met with here, inhabits an upright muddy tube 

 attached at the lower end. The whole length of this tube was 

 covered by the dead-men's fingers, which in some instances grew 

 out from the lower end of the tube into the usual irregularly 

 ramifying masses. This symbiosis was no fortuitous occurrence, 

 but was invariable throughout the whole of the central portion 

 of the North Sea where these two forms are everywhere to be 

 found." On the coasts of Scotland and Jutland, on the other 

 hand, Alcyoniwn occurred in its ordinary form. The common 

 Virgularia mirabilis, found at depths of 50 to 100 metres, 

 with a temperature of 7°-8° C, was the only sea-pen met with 

 in the area examined, but we obtained a fairly large number 

 of individuals. 



Sponges constitute a group of attached forms abounding 

 in individuals, though remarkably poor in species ; they cannot 

 be said to be regularly distributed, but are more or less local. 

 On the north side of the Great Fisher Bank in particular 

 we got enormous quantities of a ramifying whitish form 

 [Halickojidria panicea van bibitla)} The different variations of 

 Ficulina {^Siiberites) fiats are, however, the most prevalent. 

 The commonest of these variations, where the sponge grows 

 round shells and gives shelter to the hermit crab Pagiiriis 

 pubescens, are comparatively scarce in the central portion of 

 the North Sea, and we came across them at only one or two 

 stations, but in the more northern parts of the North Sea 

 plateau they were plentiful. Another variety, attached to 

 empty shells of the sea-tooth [Anfa/is entalis) which as a rule 

 shelter the gephyrean Phascolosoma strovibi, was abundant at 



^ Urttcina crassicornis, Metridiuin dia>it/uis, chiefly found on large shells of Mytihis modiolus 

 and NepUinea, Boloccra tuedia and Chondradinia digitata on shells of Neptunea and Sipho ; at 

 one or two stations (depth about lOO metres, temperature slightly over 6° C. ) we got Zoatithns. 



^ Several of these overgrown tubes were empty, which looks as if the worm benefited least 

 by the symbiosis. 



^ Thanks to information kindly sent me by Professor Plate, Berlin, I can add H. panicea 

 forma typica as being common on the Great P'isher Bank ; this form was also abundant on the 

 northern slope of the Dogger Bank. 



