The Black Pill Millipede,Glomeris marginata, is the best studied millipede species and a model organism for Diplopoda.Glomeris marginatais widespread, with numerous colour morphs occurring across its range, especially in the south. This study investigates whether colour morphs might represent cryptic species as well as the haplotype diversity and biogeography ofG. marginata. The results of the COI barcoding fragment analysis include 97G. marginata, as well as 21 specimens from seven potentially related species:G. intermediaLatzel, 1884,G. klugiiBrandt, 1833 (G. undulataC.L. Koch, 1844),G. connexaKoch, 1847,G. hexastichaBrandt, 1833,G. maerensAttems, 1927,G. annulataBrandt, 1833 andG. apuanaVerhoeff, 1911. The majority of the barcoding data was obtained through the German Barcode of Life project (GBOL). Interspecifically,G. marginatais separated from its congeners by a minimum uncorrected genetic distance of 12.9 %, confirming its monophyly. Uncorrected intraspecific distances ofG. marginataare comparable to those of other widespreadGlomerisspecies, varying between 0–4.7%, with the largest genetic distances (>2.5 %) found at the Mediterranean coast. 97 sampled specimens ofG. marginatayielded 47 different haplotypes, with identical haplotypes occurring at large distances from one another, and different haplotypes being present in populations occurring in close proximity. The highest number of haplotypes was found in the best-sampled area, western Germany. The English haplotype is identical to northern Spain; specimens from southern Spain are closer to French Mediterranean specimens. Analyses (CHAO1) show that approximately 400 different haplotypes can be expected inG. marginata. To cover all haplotypes, it is projected that up to 6,000 specimens would need to be sequenced, highlighting the impossibility of covering the whole genetic diversity in barcoding attempts of immobile soil arthropod species.
