XIX. 



CHARACTERISTIC DEEP-SEA TYPES. — ECHINODERMS. 



HOLOTHURIANS. 



The order of Apoda among liolotliurians has neither pedicels 

 nor suckers, while the Pedata have a highly developed ambula- 

 cral system and a well-defined dorsal and ventral surface, with 

 pedicels scattered over the whole body. The large lobes of the 

 Elasipoda (the new order of deep-sea holothurians established by 

 Dr. Theel) are perhaps tactile. The ventral surface of the Ela- 

 sipoda is intended for locomotion, and, as suggested by Dr. 

 Theel, they probably move along the bottom with the actinos- 

 tome wide open, constantly filling their alimentary canal with 

 the ooze stirred up by the tentacles of the mouth. The cal- 

 careous deposits resemble those of the larval holothurians, and 

 they possess other features showing them to be an embryonic 

 type. The auditory capsules are often present in great num- 

 bers. 



The Elasipoda are strictly abyssal types, no member of the 

 group having been dredged in less than 50 fathoms, and that 

 only in the Arctic Ocean, where, as we know, deep-sea types are 

 found in comparatively shallow Avater. Of the large number of 

 " Challenger " species, only five are found within the 500-fathom 

 line, as many more inside the 1,000-fathom line, and the others 

 all below that limit. At the localities where the " Blake " was 

 fortunate enough to find Elasipoda, they occurred in large num- 

 bers, and, judging from the contents of the trawl, they appar- 

 ently live in communities including several species, and prefer 

 soft ooze. The experience of the " Challenger " and of the Fish 

 Commission was a similar one. The " Challenger " obtained on 

 one occasion no less than ten species associated together. 



