INVERTEBRATE BOTTOM FAUNA 



483 



:%^i 



and so is the sponge TJienea inuricata (see Fig. 342), which adheres to 

 the mud by means of long outgrowths, and the worm-like gephyrean 

 Sipunculiis priapuloides. 



Thus the majority of the mud-fauna in the deep parts of 

 the fjords, owing to the nature of the bottom, 

 consists of unattached animal forms, most of 

 the sponges, corals, hydroids,^ bryozoans, 

 ascidians (including the unattached molgulids), 

 and brachiopods being absent ; in other words, 

 the nature of the bottom gives the fauna its 

 character. Still even here it is possible for 

 certain attached forms to occur normally, and 

 very often abundantly. There are frequently 

 great quantities of the little mussel [Area 

 pectiuiciLloides), which fastens itself by its 

 byssus-filaments sometimes to the larger for- 

 aminifera, sometimes to slag from steamers, 

 or any other hard substances which it happens 

 to come across in the mud. There are also 

 numbers of the white semi-transparent Peden 

 abyssorimi, which occurs, according to Sars, 

 also in the deepest parts of the Christiania 

 fjord, where it attaches itself to rotten bits 

 of sea- weed. 



I shall now turn to the faunal conditions 

 in the fjords where there is hard rocky 

 bottom, i.e. the more or less steep sides of 

 the fjords and the submarine ridges or emin- 

 ences. These latter are sometimes isolated 

 raised portions of the floor surrounded on 

 all sides by softer bottom, and sometimes 

 spurs running out from the walls of the fjord. 

 The slopes of the ridges and eminences are 

 frequently covered with coarse sand and 

 stones, as are also the sides of the fjords 

 where not too steep. In many cases, how- 

 ever, the walls go down so steeply that no 

 loose deposits occur till we reach. a depth of 

 several hundred metres. 



The fauna here is quite different from that on the muddy 

 bottom, consisting mostly of attached forms of various groups, 



^ Only a little form {Perigoniimis abyssi) is common here, attached to mussel shells, 

 ■especially those of Nticula tuviidula. 



Fig. 341. 

 Kophobelevinonstelliferum, 

 O. F. Miill. (After 

 Asbjornsen. ) 



