STARFISH, SEA URCHIN, BRITTLE STARS 99 



A characteristic feature of the sea cucumlDers is the much- 

 branched tentacles about the mouth (Fig. 51). The 

 tentacles vary in number from eight to twentj' and some- 

 times more. These are supposed to be much-modified 

 tube feet, and are used to push food into the mouth. When 

 the animal is disturbed, they can be 

 greatly contracted and drawn completely 

 back within the mouth. 



Sea cucumbers vary from two to fifteen 

 inches in length, depending upon the 

 species and the age of the individual. 

 One species of Cucumaria sometimes 

 attains a length of three feet and is 

 orange-red in color. 



Feather stars. — This group of echino- 

 derms comprises the lowest representa- 

 tives and at the same time the oldest 

 members of the branch. The feather 

 stars, crinoids, or sea lilies as they are 

 variously called, are found as fossils in 

 the rocks of the paleozoic age and weie 

 very abundant in the past. The living 

 forms are few and, for the most part, 

 inhabit the deeper regions of the sea. It 

 is a characteristic of the crinoids that 

 they are attached to objects ui the sea, Fiq- 52. — Seauiy. 

 either for a short period of their life, or permanently. 

 Most of the species are permanently attached to submarine 

 objects by a stem, which frequently is very long, and 

 made up of a series of joints perforated by a central canal. 

 The body (Fig. 52), borne on the enrl of the stalk, has the 

 oral side uppermost, which position, it will be recalled, is 



