144 ANIMAL FORMS 
star, especially one of the basket-stars, by its dorsal side 
toastalk. In the crinoids the numerous branches of the 
arms are compara- 
tively short, and in 
the arrangement of 
the internal organs 
there are numer- 
ous differences, but 
for all that the re- 
semblance of these 
organisms to the 
other echinoderms 
is undoubted. 
138. Haunts. — 
The greater num- 
ber of  starfishes 
occur alongshore, 
slowly crawling 
; about in search of 
Fie. 90.—Sea-urchin shi (eal purpuratus). foo d, or concealed 
in dark crevices of 
the rocks, where they may often be found as the tide goes 
out, and we know that in gradually lessening nnmbers other 
species lead similar lives at different levels far down in the 
dark and gloomy depths. In these same locations the sea- 
urchins occur, sometimes singly, but more usually associa- 
ted in great numbers, several species excavating hollows in 
the rocks, within which they obtain protection. The brit- 
tle-stars and sea-cucumbers may also be found occasionally 
in open view, but more often they make their way about in 
search of food buried in the sand. The crinoids are usual- 
ly inhabitants of deeper water, where they are found asso- 
ciated often in great numbers. A few species upon attain- 
ing the adult condition separate from the stalk, and are 
able to move about (Fig. 95), but the remaining species 
never shift their position. 
