Abstract
Using molecular markers and species delimitation analyses, a high diversity of bi-tentaculate Cirratulidae was discovered from the North-East Atlantic. Five new species are described: Chaetozone pseudosetosa sp. nov., Chaetozone quinta sp. nov., Chaetozone barentsensis sp. nov., Chaetozone monteverdii sp. nov., and Chaetozone chambersae sp. nov. Several morphogroups are also described, even though the presence of cryptic diversity prevented naming of individual species. For each species presented, a molecular diagnostic is given from the universal barcode COI and, when available, the D1-D2 domains of the 28S rRNA. This increases the number of species in Chaetozone in northern European waters from ten to at least 17 species, the exact number of species remaining uncertain as taxonomic issues with older names remain unresolved.