Arctic Pholoe (Polychaeta: Pholoidae): When integrative taxonomy helps to sort out barcodes

Pholoe longa (O.F. Müller, 1776) and Pholoe minuta (Fabricius, 1780), two of the earliest described polychaete species from the Arctic, are redescribed. Freshly collected specimens from the type locality in Western Greenland were used for a combined morphological and molecular approach to reassess the identity of the species, and to study their phylogeny and distribution. Illustrated descriptions are presented and neotypes are designated. Staining with Shirlastain A was found to be an appropriate method for confocal laser scanning microscopy (CLSM) studies. An extended data set, including publicly available data along with our newly provided sequences, was analysed. It was revealed that taxonomic problems had obviously prevented the correct designation of barcodes in public databases, and consequently a number of entries are suggested to require correction. Phylogenetic reconstructions and species delimitation analyses based on cytochrome c oxidase subunit I (COI) data revealed the occurrence of at least seven species of Pholoe in the Arctic and subarctic regions, with P. longa and P. minuta among them. Pholoe longa shows a broad distribution and a geographic pattern in the COI network, but has low genetic divergence. Pholoe minuta exhibits a narrow distribution range, but has high genetic divergence with a large number of low-frequency haplotypes. The geographic pattern observed for P. longa suggests a strong influence of the last ice ages on the distribution in the Arctic.