. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. INVERTEBRATE BOTTOM FAUNA 483. and so is the sponge Thenea muricata (see Fig. 342), which adheres to the mud by means of long outgrowths, and the worm-like gephyrean Sipunculus 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,1 bryozoans, ascidians (includ
. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. INVERTEBRATE BOTTOM FAUNA 483. and so is the sponge Thenea muricata (see Fig. 342), which adheres to the mud by means of long outgrowths, and the worm-like gephyrean Sipunculus 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,1 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 pectunculoides), 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 Pecten abyssortim, 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, 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 m
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