. 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. "Michael Sars" North Atlantic Deep-sea Expedition (1910); Oceanography; North Atlantic Ocean. 472 DEPTHS OF THE OCEAN grows. Litto7'ina littorea and L. obtusata again are found in greatest abundance wherever there is shelter, while Nacella pelliicida generally lives on the blades of Laminaria hyperborea. In the sheltered haunts of Lmnmaria saccharina and L. digitata, particularly on the first named,
. 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. "Michael Sars" North Atlantic Deep-sea Expedition (1910); Oceanography; North Atlantic Ocean. 472 DEPTHS OF THE OCEAN grows. Litto7'ina littorea and L. obtusata again are found in greatest abundance wherever there is shelter, while Nacella pelliicida generally lives on the blades of Laminaria hyperborea. In the sheltered haunts of Lmnmaria saccharina and L. digitata, particularly on the first named, we find the brittle-star OpJiiothrix fragilis, while the localities with L. hyperborea have evidently no attractions for it; the blades of L. saccharina, too, are much patronised by the bryozoan Aetea. Asterias glacialis (see Fig. 334) also prefers sheltered localities. Why there should be these apparently capricious affections is as yet un- known, but it may be that in undisturbed waters there are higher temperatures during the summer, and that consequently various influences are brought to bear upon the organisms at one stage or another of their lives. The most typical localities of this kind are met with as portion of the a in sounds amongst the skerries, where there is a more or less strong current, which carries away the finer particles of mud that would otherwise settle, and leaves only large fragments of shells and similar debris. On the hard bottom there are usually numbers of both attached and unattached forms, chiefly consisting of bryo- zoans, hydroids, especially the genus Ttibitlaria, and ascidians. The coral Alcyoniiim digitatiim too is often plentiful,^ generally attached to large empty mussel shells or stones. The empty mussel shells are also patronised by big colonies of the serpulid Pomatoceros triqueter, which however is just as much at home on the rocks up to the very shore. There are, besides, Anoinia ephippittm, Chiton cinereus, Tectura virginea, Bu
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