290 DEEP-SEA ECHINODERMS 



fied to suit the peculiar conditions under which they 

 live, but they also retain certain ancestral leanings 

 which have been lost by their more modern adult- 

 relatives of the shallow water, and are devoid of 

 certain specially- Holothurian characters which the 

 latter have acquired. These Elasipods, of which 

 fourteen species have been dredged by the Investigator 

 in depths ranging from 200 to 2000 fathoms, have, in 

 fact, more the shape of large slugs than of ordinary 

 Holothurians. Their body is bilaterally symmetrical : 

 its ventral surface, where alone tube-feet are found, 

 forms a broad, flat sole for crawling, the breadth of 

 which is often increased by a marginal fringe or fin ; 

 the back is usually humped ; and, as in a crawling 

 animal, the mouth is either situated upon or turned 

 towards the ventral surface, to facilitate browsing. 

 Though their tissues are often as soft as jelly, yet 

 some of them, such as Deima (Fig. 90), have a 

 "shell" of calcareous plates like the test of a sea- 

 urchin on an attenuated scale. 



As regards their habits, the deep-sea Holothurians 

 gorge on mud, just as their shallow-water kindred do, 

 and some of them appear to be strongly gregarious. 



In EupyrgMS scaber, an Arctic species which is also 

 found in the Laccadive and Andaman Seas in 405- 

 738 fathoms, we have a strange geographical range 

 paralleled by that of the brittle-star Astronyx loveni 

 before mentioned. 



