36 STAR-FISHES, SEA-URCHINS, ETC. 
Class 11.—STAR-FISHES (Asteroidea). 
The star-fishes assume the most varied and curious | 
shapes. In Sand-stars (Fig. 32), the body is a mere flat-" 
tened disk, the arms branching out suddenly, often round 
and snake-like, while the feet have no suckers, and appear 
from the sides of the rays instead of the bottom. The 
Ophiacantha spinulosa is not merely a star in shape, but is 
highly luminous. Some, as the Ophiothela, divide them- 
selves spontaneously, the body looking as if it had been 
chopped in two; the two halves become separate indi- 
viduals, new arms growing from the severed parts. In 
one of the brittle stars, known as the basket-fish, the arms 
are divided into many branches of twos—bifurcating, as it 
is called—and resemble, when coiled, a ball of snakes. 
They live in the coral reefs of the South, and are often 
found off the New England coast. 
Development.—The young are produced from eggs, some, 
as Ophiocoma vivipara, appearing at once in adult form, 
Fic. 33.—Development of common star-fish. A, free-swimming form ; 
A’, later stage settling on the bottom; B, same assuming star- 
shape. 
while others (Fig. 33) are at first minute sacs swimming 
by aid of cilia, undergoing many changes, finally in two 
or three years assuming the adult shape. The common 
star-fish (Fig. 34) preys upon the oyster. 
