INVERTEBRATE BOTTOM FAUNA 493 



Special mention must be made of specimens of our common 

 sea-urchin Echimis esculentiis from two stations in the North 

 Sea: two specimens from ']'] metres, temperature 7.1° C, and 

 eight specimens from 96 metres, temperature 6.15° C. The 

 species generally varies very little, and individuals from our 

 littoral zone scarcely differ at all. Normally the shell is high 

 and of a reddish colour, while the spines are violet. The ten 

 specimens from the North Sea, however, all differed from the 

 typical form, having a flattened shape and varying considerably 

 in colour. The shell itself shows variations from the typical 

 red hue to a chocolate brown, and the spines assume every 

 intermediate shade from the most beautiful vermilion (like what 

 we find in E. elegans) to pure green. Many specimens have 

 in consequence an outward resemblance to Strongylocentrotus 

 or Echimis miliaris. Mortensen has described from the 

 North Sea (40 fathoms) two specimens of flattened shape with 

 unusually long bright red spines (like those of E. elegans). 

 Norman tells of a variety from deep water near the Shetlands 

 that had very fine spines and an exceptionally high shell, and 

 Sars has described a similar variety from the Great Edge. 



These facts appear to justify the conclusion that, whereas in 

 shallow water and along the coasts the species is of a fairly 

 constant type as regards both shape and colour, it has a marked 

 tendency to variation at greater depths, although the normal, 

 or almost normal, form is to be found also in deeper water, as 

 on the Faroe banks. The deeper portions of the North Sea 

 in particular appear to produce very striking variations. 



Of shell-bearing snails there are two forms which characterise 

 the area investigated, namely Nephmea antiqiia and Sipho 

 gracilis, both species being met with everywhere from Denmark 

 to the Scottish coast, and sometimes in great numbers.^ 

 Judging by our investigations Nephinea extends into shallower 

 water than Sipho, though both species exist plentifully side by 

 side at considerable depths. One biological peculiarity worth 

 recording was that every individual of Sipho in the haul referred 

 to had a sea-anemone {Chondi^actinia digitata) on its shell, and 

 at other stations, too, they were found living together in 

 symbiosis. These sea-anemones were likewise found on the 



Norwegian depression, from the Danish coast, and east of Aberdeen in 62 metres), Eckmaster 

 sangumolenius, Sti'ongylocentrotus drobachiensis (only from the Danish coast, one specimen with 

 Stylifer tiirtoni on its shell), Echinus esculent us var., Echinocyamus pusillus (only east of 

 Aberdeen in 62 metres), Cucwnaria lactea. 



^ We secured 130 specimens of Neptunea and 375 of Sipho at one haul from a depth of 96 

 metres (temperature 6.15° C. ). 



