THE BRITTLE STARS 



Starfish are sluggish animals, rarely moving of themselves, and staying for 

 days in the same position. Those kept in tanks or in glass vessels prefer to cling 

 to the side, instead of lying on the bottom. When disturbed, however, a starfish 

 can travel at a considerable pace. Those starfish that have suckers crawl by means 

 of their tube feet, while those that have no suckers still use their tube feet slightly, 

 but also progress by the muscular movements of the rays. The short-armed 

 Asterina and Astropecten can right themselves in less than a minute, and accomplish 

 the act by raising themselves on the tips of four rays, and then turning a somer- 

 sault by throwing over the fifth ray. Asterias takes rather longer, and effects its 

 purpose by first twisting over one or two of the rays and catching hold of the 

 ground by the suckers. It then gradually turns over the rest of the body. 

 Cribrella rights itself in the same way as Asterias, but, apparently because of the 

 stiffness of its skeleton, takes much longer over the process. Starfish, like other 

 echinoderms, are a sociable class. 

 Even the deep-sea forms sometimes 

 live in swarms. Many shallow-water 

 forms also are gregarious, and some 

 species have been observed to pair at 

 the breeding season. The deep-sea 

 starfish, writes Alcock, "subsist 

 largely on mollusks, the shells of 

 which, along with the chitinous re- 

 mains of prawns and amphipods, are 

 often to be found in their stomachs; 

 but some of the characteristic deep- 

 sea forms appear to gorge themselves 

 with globigerinaooze." The shallow- 

 water forms prefer hard ground, 

 rocks, reefs, or beds of hard sand, 

 where they find in abundance the 

 mollusks and small crustaceans on 

 which they feed. 



Between the Asteroidea and Ophiuroidea, the family Brisingidce has been con- 

 sidered by some a link; but in all essential features of structure they agree with the 

 Asteroids. Superficially they resemble the Ophiuroids in having long, thin, flexi- 

 ble arms, clearly distinguished from the small central disc or body. 



THE BRITTLE STARS Class Ophiuroidea 



The name Ophiuroidea, given to the brittle stars, refers to their long serpent- 

 like arms which are attached to a relatively small and usually rounded body or disc. 

 The digestive and generative systems do not extend into the arms, but are confined 

 to the body; so that the arms are appendages to the body, rather than portions of 

 it. They are cylindrical, and have no groove on the under side, such as exist in 

 starfish, but have little openings through which the tube feet pass. In this class it 



STARFISH TURNING OVER. 



