ECHINODERMA 9 



In the Indo-Pacific regions several species of sea-cucumbers are 

 eaten, mainly by the Chinese ; only the skin is used, dried and 

 smoked (" beche de mer," " trepang "). 



Most echinoderms lend themselves excellently for preserva- 

 tion in a dried state ; they ought, however, first to lie in alcohol 

 or formalin for a few days. Formalin ought not to be used for 

 j^reserving echinoderms for any longer time, because, if not 

 neutralised, it dissolves the calcareous structures ; it is, however, 

 excellent for preserving sea-stars, in so far as it keeps the colour 

 fairly well, which is alwaj^s lost on using alcohol. If then sea-stars 

 are dried after having been preserved some days in formalin 

 they may keep their colour fairly well (though not all species). 

 Sea-cucumbers should always be preserved in alcohol. 



On account of the strongly developed calcareous skeleton the 

 echinoderms are among the commonest of fossils, especially sea- 

 lilies and sea-urchins. They occur in all formations, from the 

 oldest fossiliferous deposits to the most recent geological forma- 

 tions. During the glacial epoch numerous such fossils (especially 

 sea-urchins of the genera EcJmiocorys {Ananchytes) and Conulus) 

 from the Cretaceous formation were scattered all over the 

 countries of northern Europe, carried along by the ice. Such 

 earth-found specimens have plaj^ed a great part in folk-lore ; 

 they were regarded as thunder-stones, fallen from heaven 

 with the thunder, and supposed therefore to protect against the 

 thunder. They were also used in prehistoric times as amulets. 



The echinoderms are generally divided in two main groups : 

 the Stalked Echinoderms or Pelmatozoa (sea-lilies and their fossil 

 relatives, the Cystidea and the Blastoidea) and the Free-living 

 Echinoderms or Eleutherozoa (sea -stars, brittle -stars, sea-urchins, 

 and sea-cucumbers). A more recent classification distinguishes 

 three main groups : Pelmatozoa (sea-liUes, etc.), Asterozoa (sea- 

 stars and brittle-stars), and Echinozoa (sea-urchins and sea- 

 cucumbers). None of these classifications, apparently, represents 

 quite correctly the mutual relationship of the classes. It would 

 seem more probable that sea-stars and brittle-stars are closely 

 related and form one natural group, with which again the sea- 

 urchins are. somewhat more distantly, connected, whereas sea- 

 cucumbers and sea-lilies are not very closely related with this 

 group or with each other. 



Key to the Classes of recent Echinoderms. 

 1, Attached by means of a stalk, at least in the j'ounger stages. 

 Arms feather-shaped . . Sea-lilies or Crinoids (Crinoidea) 



Free -living, no stalk. Arms not feather-formed, or wanting 2 



