Abstract
The karyotype of the common ragworm Hediste diversicolor (OF Muller 1776) (Polychaeta, Nereididae) was determined for the first time; it comprised 8 metacentric, 2 submetacentric and 4 subtelocentric chromosome pairs. In a few metaphases, we observed an easily distinguishable undersized supernumerary chromosome. Recent taxonomic revisions of the family Nereididae have highlighted the need for further studies in several genera. To understand the taxonomic relationships in this family, we carried out a comparative karyological analysis through multivariate analyses (principal component analysis and hierarchical cluster analysis), using morphological and structural features of karyotypes, between H. diversicolor and 10 other Nereididae species. This analysis showed the distinctiveness of H. limnicola, H. diversicolor and Nereis oligohalina, which could be explained by the presence of 3 or 4 morphological categories of chromosomes in these species. The remaining species presented more symmetrical karyotypes with only 2 morphological categories and were grouped in 2 main clusters, mainly due to different percentages of metacentric chromosomal pairs. This study highlights the importance of cytogenetics in taxonomic studies of polychaetes.