18 LIFE IN THE SEA [OH. 



comparatively small area of sea-bottom. Among the 

 attached forms we find the algae, the zoophytes and 

 polyzoa, the sponges, the reef-building and solitary 

 corals, the sea-anemones, the branching corals and 

 alcyonarians, the crinoids, some Crustacea of which 

 the barnacle is the most familiar example, many 

 molluscs such as the cockle, mussel and oyster and 

 most of the tunicates. Among the burrowing forms 

 are some protozoa, many worms, some sea-urchins, 

 and sea- cucumbers (Holothurians), some sea-anemones, 

 many Crustacea, and many molluscs such as the clams 

 or razor-shells. The sluggish, slowly moving, bottom 

 living animals include the starfishes and most of the 

 sea-urchins, crabs, lobsters and hosts of other Crustacea, 

 many worms, many molluscs such as the scallops, 

 periwinkles and whelks. Some fishes are also to be 

 placed in this category. Benthic animals thus include 

 representatives of all the great groups of life. When 

 we remember that distinct faunas are to be found 

 on sea-bottoms of different depths, and of different 

 physical conditions, we see that it is convenient to 

 speak of littoral, shallow water, deep water, and 

 abyssal benthic populations. In the wider economy 

 of the sea all these categories of life are distinct from 

 each other. 



Now the great majority of marine animals are 

 mthic in habit but there are a number which possess 

 >werful locomotory organs and which are thus able 



