Variation in Nymphon brevirostre (Hodge), and the status of N. rubrum (Hodge) (Arthropoda: Pycnogonida)

A series of morphometric analyses conducted on specimens of Nymphon brevirostre Hodge and Nymphon rubrum Hodge from British waters has shown that the characteristics variously used in the past to distinguish these two species are invalid. In this material these characteristics range from the extreme of the typical N. brevirostre form to that of the typical N. rubrum form, with most of the specimens exhibiting an intermediate morphology. Multivariate analyses showed no significant splitting of the material into two groups which might correlate to Hodge's two species. Protonymphon larvae from males of both typical extreme forms were morphologically identical. It is concluded that N. rubrum is a junior synonym of N. brevirostre, a variable species whose morphology tends towards the rubrum form as the animal grows.