Morphological differentiation in the ragworm,Hediste diversicolor(Polychaeta, Nereididae), as revealed by variation of paragnath number and distribution

Variation in the number and distribution of paragnaths in populations of the ragworm, Hediste diversicolor, from 14 localities across a large part of its European range was analysed. Significant inter‐population variation was revealed by ANOVA applied to (i) the number of paragnaths in each zone of the pharynx, (ii) the number of paragnaths in each of the two belts (maxillary and oral), (iii) the total number of paragnaths on the pharynx and (iv) the measures of asymmetry for paired zones. No geographical pattern of morphological variation was detected by multidimensional scaling on population centroids and no signals of morphological population substructuring were found. Explanations of variation in paragnath number and pattern among populations may reflect local differences in diet or dominant mode of feeding. Factor analysis suggested that the two belts of the pharynx behave as separate functional units in feeding activities. The comparison with two samples of the other nereidid, Perinereis cultrifera, showed only a moderate distinction between the two species. We recommend use of the paragnath pattern and number coupled with other kinds of markers when addressing the analysis of species boundaries or subtle population differentiation.