CHAPTER VI 



THE STARFISH FAMILY. (Optional) 



56. The Starfish Group. — This group of animals includes 

 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, echinus, 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 cal- 

 careous plates. In some 

 forms, like the starfish, 

 the plates 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 over the body giving 

 the spiny appearance char- 

 acteristic of the group. 



Both the skeleton and soft parts are arranged in a radial 

 manner. The presence of spines and the radial arrange- 

 ment are two characters by means of which one can 

 recognize most of the echinoderms. 



57. The Starfish. — Starfishes are found in salt water. 

 They are composed of a central region, called a disk, from 



71 



Figure 71. — Starfish. 



