HOLOTHUROIDEA 



61 



more worm-like in appearance. Some are so long and slender 

 that they are sometimes thought to be worms. 



The size varies from | inch in one species found upon the 

 Massachusetts coast, to 3 feet, in another species found in 

 Monterey Bay, California. 



The body wall is tough, leathery, muscular, and not so rigid 

 as in the starfish or sea-urchin, although minute calcareous 

 spicules are scattered throughout it. 



The tube-feet may be in rows, or scattered, or entirely want- 

 ing, depending upon the species, of which several hundred are 

 recorded. The sea-cucumbers 

 move with their long axis parallel 

 to the ground. They creep along 

 with the help of the tentacles. 



Protective Resemblance. 

 Their colors, which are reddish 

 brown or yellowish, harmonize 

 so closely with those of their en- 

 vironment that their protective 

 resemblance is almost perfect. 

 As the animals rest on the bot- 

 tom of the sea with their feathery 

 tentacles spread out they closely 

 resemble the vegetation of the 

 sea bottom. A person may 

 stand within a foot of the sea- 

 cucumber and not see it. 



The alimentary tube (Fig. 47) 

 is several times the length of 

 the animal, and the intestine is 

 coiled in a uniform manner. 



The food of the holothurians consists of organic matter 

 obtained from the sand which they swallow, or of small animals 

 which they capture with their tentacles. They are nocturnal 

 in their feeding habits, resting quietly during the day on the 

 bottom of the sea or buried in the sand. 



The respiratory system consists, probably, of the so-called 

 " respiratory trees," two hollow, much-branched organs open- 

 ing into the cloaca, which is periodically filled with water. 



Fig. 47. -^-Sea-cucumber (Holo- 

 thuriari) dissected to show ali- 

 mentary tube, al.t. (Leuckart.) 



