The Colours of Ophiocomina Nigra (Abildgaard): I Colour Variation and its Relation to Distribution

Abstract

The ophiuroid, Ophiocomina nigra, is noted for its variability of colour, a phenomenon most pronounced where the species also has its greatest distribution in depth. Observations have been made on two geographically distinct populations, from the vicinities of Millport and Plymouth. The body colour of the observed animals ranges in a continuously graded series from black to orange-yellow. While both populations exhibit analogous variations, there is a distinct difference in the range and tone of coloration which each displays. It is suggested that this geographical difference is correlated in some degree with differences in colour tone of the substratum. It was observed that the incidence of light-coloured phases in each population increased with increasing depths, and some statistical evidence supports this conclusion. Thus, at least two factors, depth and substratum, may affect the distribution of colour variations in O. nigraIn addition to the variations in general body colour, there are two distinct colour patterns found on the disk. These are probably truly polymorphic and may be of cryptic value.A scheme of colour classification is described which facilitates observations in the field and in the laboratory.