OPHIUROIDEA 



175 



var. Insitanica Ljungman, and var. Abildgaardi Koehler. To 

 characterise all these varieties briefly is impossible, and as, more- 

 over, they are by no means constant, and are connected by all inter- 

 mediate forms, it ma}^ suffice to refer to the detailed descriptions 

 given by Koehler in his '"Echinodermes" in Faune deFrance (pp. 75- 

 77), or in Les ^chinodermes des mers d' Europe (i. pp. 267-77). 



This very common species occurs mainly on hard bottom, and 

 is often found in empty shells, among Serpulids, etc. ; also under 

 stones on the shore. It is able to press itself into small cavities, 

 from which it is hardty possible to remove it without breaking it 

 to pieces, the more so as its arms very easily break off. Its food 

 consists mainly of worms and Crustaceans, but it also eats small 

 mussels, echinoderms, compound Ascidians, Foraminifera, etc. 





Fig. 98. — Ophiothrix JragUis ; part of oral and dorsal side. x 8. 



It appears that ciliary currents also play some role in catching 

 food (detritus). It is eaten specially by Liiidia ciliaris. 



The larva (Fig. 88, 1) is very characteristic owing to its long, 

 sidewards -directed, postero-lateral arms, which are provided with 

 2-3 broad, dark pigment spots ; the other arms are short, unpig- 

 mented. Body skeleton (Fig. 87, 3) simple ; a small, unpaired 

 process from the transverse rods. The quite young larva is 

 peculiar through the postero-lateral arms being long already 

 before any of the other arms have begun to appear ; the ciliated 

 band accordingly goes in a nearly straight line across the body, 

 above and below the mouth. On metamorphosis the long postero- 

 lateral arms are not absorbed, but serve as a floating apparatus 

 for the young brittle-star, which latter is very characteristic 

 owing to its inroUed arms and its hook-shaped spines. When 



