Vv 
DISTRIBUTION OF ANIMAL LIFE IN THE SEA 
LL 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. Hach 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, ete., 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 
23 
