CHAPTER XII 
THE STARFISH FAMILY 
Optional 
149. The Starfish Group. — This group of animals in¬ 
cludes the well-known starfish, the sea-urchins, sea-lilies, and 
several soft-bodied forms such as the sea-cucumber. The 
technical name for these different animals is echinoderm 
(e-km'6-derm : Greek, echinos , spine ; derm, skin), mean¬ 
ing spiny-skinned animals. Most of these animals have a 
skeleton. Unlike that of 
man it is on the outside 
and is composed of calcare¬ 
ous plates. In some forms, 
like the starfish, the plants 
are embedded in the skin, 
while in the sea-urchin the 
plates fit edge to edge, 
forming a shell. The plates 
support many spines which 
project out from the body 
giving the spiny appearance 
characteristic of the group. 
Both the skeleton and soft 
parts are arranged in a radial manner. The presence of 
spines and the radial arrangement are two characters by 
means of which one can recognize most of the echinoderms. 
150. The Starfish. — Starfishes are found in salt water. 
They are composed of a central region, called a disk, from 
which extend five arms or rays. On the disk is a porous 
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