Emplectonema gracile (Johnston 1837) is a hoplonemertean of marine intertidal hard-bottom communities and is distributed throughout the Northern Hemisphere. Although possessing a planktonic larval stage in its life history, the range of such cosmopolitan marine invertebrate species is often explained by cryptic speciation and anthropogenic transport. The purpose of this study is to test for possible cryptic species using mtDNA markers (COI and 16S rDNA) and to investigate population structure in E. gracile over a portion of its geographic range using mtDNA markers and ddRADseq nuclear SNP data. The results of both phylogenetic- and tree-based species delimitation revealed that E. gracileis a morphotype containing cryptic species. Three North Atlantic and one Pacific coast population are inferred as one species (E. gracile sensu stricto) and two Pacific coast populations (Akkeshi, Japan and Charleston, Oregon) are inferred as another species (Emplectonemasp 1), strongly confirming an earlier study and extending the range of the latter species to the Pacific coast of Japan. Anthropogenic transport is suggested as the likely mode of transport for E. gracile.Both Fst, PCA and haplotype network analyses suggest a lack of differentiation between E. gracile populations separated by large geographic distances.In contrast corresponding analyses forEmplectonemasp. 1 indicate differentiation between the two populations sampled. Further research will be necessary to reveal if rare anthropogenic transport or natural dispersal (larval transport, rafting) between geographically adjacent yet to be delimitedE. gracile morphotype populations is responsible for its seemingly disjunct distribution.