A fragment of the cytochrome c oxidase subunit I (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.