ECHIXODERMS. 



43 



^ ' '' 



a character as to readily explain the other name, " serpent-stars,"' which 

 is frequently applied to them. Indeed, the scientific name of the group. 

 Ophiuroids (serpent-like), alludes to this very character. 



In both serpent-stars and true starfish each of the arms, as well as the 

 disc itself, is strengthened by an external skeleton of plates of carbonate 

 of lime which may bear spines and 

 other protective structures. Concern- 

 ing the brittle-stars there is little of 

 general interest to be said. About 

 four hundred and fifty species are 

 known from the whole world. The 

 general appearance of the great ma- 

 jority is shown by the adjacent cut; 

 but there is one group of forms, the 

 so-called basket-fish, which differ con- 

 siderably, for the arms branch again 

 and again, so that the number of ter- 

 minal branches is enormous. Usually, 

 the number is stated in the books as 

 eighty thousand, but this seems to be 

 much too large, for Mr. Lyman, who 

 recently investigated the subject, has 

 shown that the number is less than 

 six thousand. The common name, 

 "basket-fish," is suggested by the 

 shape the animal takes when drawn from the water. Its many arms 

 roll upwards and inwards, making the resemblance to a shallow basket 

 quite marked. Old Governor John Winthrop first described the species 

 from a specimen obtained near the shoals of Nantucket, calling it net- 

 fish as well as basket-fish. Their colors are not very attractive, dull 

 yellows and browns prevailing. 



A little more interest attaches to the true starfish, for they are known 

 to every visitor at the shore. Their five spiny arms, the red, orange, or 

 purple colors, and the curious little coral-like spots make them attractive, 

 while the immense numbers of them to be found on the mud fiats, and 

 especially on the mussel and oyster beds, after the tide has gone out, only 

 increases the interest in them. At favorable localities the whole bottom is 

 covered with them. One of the most common questions concerning them 

 is, '-'What do they live on?" and the answer that their food consist- of 

 mussels, oysters, and other shell-fish only increases the curiosity. The 

 question concerning; the diet of the shell-fish themselves never arises, — 



Fig. 44. — A brittle-star (Opiothrix). 



