16 THE HAUNTS OF LIFE 
OF UNCERTAIN POSITION.—There are many 
seashore animals whose relationships are ob- 
scure. Thus there are the Polyzoa, to which the 
common Sea-Mat (Flustra) belongs—the ani- 
mal on which Darwin wrote his first scientific 
paper. The Polyzoa form a large class, with 
a great variety of representatives, some sea- 
weed-like (Flustra), till you look into them; 
some coral-like (Cellepora) ; some gelatinous 
(Alcyonidium) ; some like zoophytes (Gemel- 
aria), but ever so much higher in structure. 
ECHINODERMS.—The prickly skinned ani- 
mals are represented by star-fishes, brittle-stars, 
sea-urchins, and sea-cucumbers, forming a well- 
marked “‘kenspeckle” class, with a great tend- 
ency to become very calcareous, least so in the 
sea-cucumbers, most in such sea-urchins as the 
sand-dollar. It is a most interesting sight to 
watch the common star-fish creep up the verti- 
cal surface of a submerged rock by means of its 
remarkable hydraulic locomotor system, while 
the sea-urchin, when moving on a flat surface, 
hobbles along on the tips of its five teeth! 
STINGING ANIMALS.—Sea-anemones nestle 
like flowers in the niches of the rocks. In 
