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ECHINODERMS OF THE BRITISH ISLES 



1. Ophiomitrella clavigera {Liungma,n) . (Fig. 103.) 



(Syn. Ophiactis clavigera Lj ungmaii ; Ophiolebes claviger(L\ ungman) ; 

 Ophiomitrella cordifera Koehler ; Ophiolebes acanellce Verrill.) 



Scales of disk simply imbricating, carrying short, thorny 

 stumps. Radial shields contiguous. Dorsal plates of arms small, 

 rhombic, widely separated by the lateral plates which join in the 

 mid-line. Ventral plates with slightly excavated outer edge, gener- 

 ally widely separated ; sometimes, however, the proximal ones are 

 almost contiguous. Five to six arm spines, the upper ones of which 

 are the longest, somewhat longer than an arm segment ; they 

 may, however, be somewhat shorter and thicker than shown in the 



Fig. 103. — Ophiomitrella clavigera. (a) Part of oral, (6) of dorsal, side. 

 X 9. (After Th. Mortensen, Scand. Echinod.) 



figure, also they are more or less serrate. One small tentacle 

 scale. Mouth shields small, rhombic, or more or less irregular. 

 Adoral plates large. The disk is, in adult specimens, as a rule 

 much swollen. It reaches a size of ca. 7 mm. diameter of disk ; 

 the rather robust arms are 4-5 times the length of the diameter 

 of disk. Colour in life unknown ; in alcohol, whitish. 



This species is viviparous, and a proterandric hermaphrodite. 

 A remarkable (undescribed) Crustacean with four egg-sacs lives 

 as a parasite in it ; the infected specimens are totally castrated 

 by the parasite. 



In British seas this species has been found off S.W. Ireland in 



