DISTRIBUTION OF ANIMAL LIFE IN THE SEA 



AiL living things which inhabit the sea have their appointed 

 boundaries, and the localization of marine life is as distinct 

 as is that of terrestrial life. Each kind of beach has forms of life 

 peculiar to itself. Those animals which inhabit rocky shores or 

 stony beaches or sand or mud may be looked for anywhere under 

 similar physical surroundings. They are, however, modified by 

 climatic conditions, and in wide ranges differ in genera and 

 species. The rocky coast of Maine has a class of sea-urchins and 

 starfishes which are different from those which live on the rocky 

 shores of the northern Pacific coast, yet they are all easily recog- 

 nized as belonging to the same family, and a description of 

 typical forms is a sufficient guide to the recognition of their 

 relationships. 



A bathymetrical division defines the classes of animals accord- 

 ing to the depth of water in which they live. Those which live 

 near the shore are littoral species, those of the broad sea are 

 pelagic, while those living at great depths are abyssal. 



Their modes of life are distinguished by other terms. Those 

 which float at or near the surface and are carried about by the 

 currents, like the jellyfishes and the minute organisms mentioned 

 elsewhere, are plankton. Strong swimming animals which move 

 about at will are nekton. Those which are fixed, like oysters, 

 sponges, etc., and those which crawl on the bottom, like crabs, 

 echinoderms, etc., are benthos. 



Again, geographical divisions are named, in recognition of 

 climatic influences. The boreal fauna and flora on the Atlantic 



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