178 



ECHINODERMS OF THE BRITISH ISLES 



1. OpUocomina nigra ( Abildgaard) . (Fig. 83, p. 145 ; Fig. 100.) 



(Syn. Ophiocoma nigra (Abildg.) ; 0. granulata Forbes ; 

 0. Nilssoni Miill. and Troschel ; 0. RascJii G. 0. Sars.) 



Dorsal plates of arms broad, contiguous, with outer edge 

 slightly rounded ; the proximal ones sometimes covered or 

 surrounded by granules. Ventral plates wdth a very obtuse inner 

 angle, the outer edge rounded or slightly concave in the middle. 

 Two tentacle scales, the outer one slightly the larger ; in the 

 distal part of arm only one, on a few of the proximal pores some- 

 times three tentacle scales. Arm spines 5-7, smooth, slender, 

 about as long as two arm joints ; the lower ones are sUghtly 



Fig. 100. — Oi^hiocomina nigra; part of oral side. x 8. 



shorter. Granules covering only the outer part of ventral side 

 of disk, the scales being distinct on the inner part. Mouth 

 shields as a rule broader than long, oval, with a rounded peak 

 on outer side ; they are, however, rather variable in shape. 

 Diameter of disk up to 25 mm. ; arms ca. five times as long as the 

 diameter of disk. Colour in life varying much, from entirely black 

 to brown or grey or even pink ; often it is more or less spotted. 



Ophiocoma Baschi G. O. Sars is the larger Atlantic form, not 

 to be distinguished from the minor 0. nigra of the Scandinavian 

 seas, mainly the fjords, by any constant character, and can 

 scarcely be maintained even as a variety. 



The larva (Figs. 87, 1 ; 88, 2) is pecuUar through having two 

 pairs of ciliated lobes ; body rods simple, end rods with one or 



