A fragment of the cytochromec oxidase subunitI (COI) gene has been used increasingly for species identification and discovery in eukaryotes. However, amplifying COI has proven difficult, or even impossible, in some taxa due to non-homology between the universal primers and the target DNA region. Among the most problematic animal groups is Serpulidae (Annelida). These sedentary marine animals live in self-secreted calcareous tubes and many of them, especially of the genus Hydroides, are economically important reef-builders, foulers, and biological invaders. We developed novel taxon-specific primers for amplifying COI from Hydroides, and for the first time generated 460-bp COI sequences from 11 of 14 species attempted. Average Kimura-2-parameter interspecific sequence distance (26.2%) was >60 times greater than the average intraspecific distance (0.43%), indicating that the COI gene is effective for species delimitation in Hydroides. Although applicability of the new primers for a wide range of serpulids needs to be tested, barcoding of Hydroides is now on its way from impossible to difficult. We anticipate that COI barcoding will provide a modern species identification tool and, combined with other molecular markers, yield important insights in phylogeny and evolutionary ecology of this large and important genus.