226 TEXTBOOK OF ZOOLOGY 



STARFISH OF CLASS ASTEROmEA 



Habitat and Behavior 



The starfish lives along the shores and in the shore waters (to a 

 depth of over 125 feet) of our stony coasts of the Atlantic and 

 Pacific, with scattered ones occurring in the Gulf of Mexico. A few 

 scattered individuals may be found on muddy or sandy shores, but 

 they are quite scarce. They are often found clinging to pilings, 

 old boats, and other objects in the water. By action of the tube 

 feet they are able to cling very tenaciously to almost any solid 

 object. At low tide they may be found under the rocks, out of the 

 sun, where they are protected from the heat and drying. Due to 

 a food relationship they are usually found in the same area with 

 marine clams, oysters, and rock barnacles. During the day they 

 are rather inactive, but at night they are much more active and 

 respond to such stimuli as light, temperature, contact, and chemicals. 

 It has been demonstrated experimentally that starfishes may form 

 habits. They ordinarily live and move about with the oral side 

 next to the substratum, and if turned over, will right themselves 

 in the same way time after time. If the arms which are habitually 

 used for this are incapacitated, they will acquire the habit of using 

 another combination of rays in this act. 



External Anatomy 



The body is composed of a central disc and some (usually five) 

 radiating arms or rays. The mouth is located in the center of the 

 under or oral surface while the upper or aboral surface is covered 

 with spines of various lengths. On the arms these spines are ar- 

 ranged somewhat in rows. Between the spines the exposed skin 

 is extended into projections known as papula or dermal dranchiae. 

 There are some small pincherlike structures, called pedicellariae, 

 arranged around the bases of the spines, which serve to keep the 

 surface of the exposed papulae clear of debris and foreign material. 

 The pedicellariae are composed of two jaws or Mades and a basal 

 plate with which the jaws articulate. There are large and small 

 pedicellariae. In an eccentric position on the aboral side of the 

 central disc is found the calcareous, sievelike madreporite. The 

 portion of the central disc and two rays adjacent to the madreporite 



