The aim of this study is to solve taxonomic problems pertaining to Spio filicornis (O.F. Muller, 1776). The original description by O.F. Muller was very brief and type material was not deposited. Based on the literature the confusion about the identity of the species has been tremendous; e.g., it was only recently realized that at least two different species from the North and Baltic Seas could be identified as S. filicornis (Bick et al. 2010). The present study is based on material collected by the authors in 2009 at the type locality in Iluilarssuk, near Paamiut, SW Greenland. Spio filicornis is redescribed in detail and illustrated comprehensively. A neotype has been designated and deposited in the collection of Rostock University. Species formerly referred to as S. cf. filicornis from the North and Baltic Seas (Bick et al. 2010) are formally described as two new species, Spio arndti sp. nov., and S. symphyta sp. nov. The morphological diagnostic characters within Spio are discussed. Information on three molecular markers (16S rDNA, 18S rDNA, cytochrome c oxidase subunit I) is also provided. The genetic divergence between the three Spio species corroborates the taxonomic discrimination.
