Distribution and genetic diversity of two earthworms, Helodrilus oculatus and Satchellius mammalis (Clitellata: Lumbricidae) in Scandinavia

We report on the Scandinavian distribution of two earthworm species, Helodrilus oculatus and Satchellius mammalis. Both appear relatively new to the Scandinavian Peninsula, as they were not included in the monographic revisions of the earthworm fauna of Sweden and Norway in the mid-1900s. We provide recent records of both species from Norway and Sweden, H. oculatus also from Denmark, and haplotype networks of four markers (COI, 16S, H3, and ITS2) are used to visualise the genetic diversity within each species. There is moderate genetic variation in COI for both taxa, and for H. oculatus, there is a West-East division between the specimens from Norway, Gothenburg (western Sweden) and Bavaria (Germany), and the ones from eastern Sweden and the Bornholm island (easternmost Denmark). This could potentially be explained by different origin and colonisation routes. In the other markers the variation is limited, and in the nuclear genes no pattern to support this split is seen. We also analyse the phylogenetic positions of H. oculatus and S. mammalis in the family Lumbricidae by combining our data (including also some 12S, 18S and 28S sequences) with a published dataset. We conclude that neither Helodrilus nor Satchellius are monophyletic. Helodrilus oculatus (type species of Helodrilus), however, forms a clade with some of its current congeners.