Morphometric analysis of two sympatric species of Perinereis (Annelida: Nereididae) from the Brazilian coast

Species definition is not an easy task, when considering the more than 27 known species concepts. Among them, the morphospecies concept has been one of the most applied since it is based on the use of observable morphological features. Morphometry has been used to delimitate morphospecies or similar taxa complementing the morphological observations and contributing to clarify taxonomic problems. Specimens from the sympatric species Perinereis anderssoni and Perinereis ponteni, collected from the north-eastern to southern coast of Brazil and considered synonymous by some authors, were compared through morphometric analyses for the evaluation of their taxonomic status. Morphometric analysis indicates that notopodial cirri lengths in the median and posterior regions on the body clearly allowed differentiation between the two species. Our results indicate that the number and arrangement of paragnaths demonstrate a pattern of variation that effectively differs and could be used to discriminate these two Perinereis species. This distinction was confirmed by the restricted among-population variability within each species, even when populations that are geographically very distant from each other were considered.