We investigated whether the different colour morphs in Harmothoe imbricata constitute a single polymorphic species or if there are several species present. We sequenced the mitochondrial COI and the nuclear ITS1–5.8SrDNA–ITS2 region from 57 specimens representing 10 distinct colour morphs collected from Svalbard to the Swedish west coast. The resulting minimum spanning haplotype network based on mitochondrial COI unequivocally shows H. imbricata to be a single and colour polymorphic species, whereas variation in the ITS region was very limited.
