92 



SYSTEMATIC ZOOLOGY 



At first the cilia cover the entire larva, but they early become 

 confined to definite bands. Many arms develop, and finally the 

 starfish begins to form, budding out as it were on one side of 

 the body of the larva (Fig. 81 ), while the larva itself is gradually 

 absorbed into the growing starfish. 



The common starfishes found in 

 the tide pools along the eastern 

 coast of the United States are usu- 

 ally only from fifteen to twenty 

 centimeters in diameter, while in 

 deeper waters they are sometimes 

 found from twenty-five to thirty 

 centimeters in diameter. But on 

 the Pacific coast there are much 

 larger species, which grow to be 

 from seventy-five centimeters to a 

 meter in diameter. Great variation 

 occurs in the size and distribution 

 of the spines, in the size and num- 

 ber of the arms, and in the extent 

 of the interradial spaces, for these 

 in some cases are almost filled up, 

 so that the animal is pentagonal 

 ( Figs. 82 and 83). In some species, 

 too, the chief axis, i.e. the axis from 

 the oral to the aboral pole, which 

 is usually short, may be much 

 lengthened in proportion to the 

 diameter of the starfish, which thus 

 appears much swollen. In color 

 there is also much diversity. Some 

 starfishes are a deep purple, others are red, or various shades 

 of yellow, orange, or light brown. The chief economic inter- 

 est in the starfishes lies in the fact that they feed upon oysters 

 and thus cause much loss to the oystermen. The practice of 

 cutting up the starfishes and throwing them back into the water 

 when they were found clinging to the oysters proved of little 

 value, for the separate pieces might each develop into a com- 

 plete animal. The starfishes possess this power to a consider- 



FlG. 81. Brachiolarian larva of the 

 common starfish, Asterias, lateral as- 

 pect, with young starfish developing at 

 tin- posterior etui; highly magnified. 

 (Drawn from life by the author.) 



