Although there are several nuisance species of serpulids reported worldwide, the present study shows that some of them have been overlooked even in geographic areas that are considered well studied. We report for the first time in Majorca the invasive species Ficopomatus enigmaticus and the first records for the Balearic Islands of the also non-native species Hydroides dianthus, H. dirampha, H. elegans and H. nigra. The most abundant species were F. enigmaticus, found at higher densities in Portixol (with up to 280 ind. m^-2), and H. elegans, found at highest densities in the port of Palma (with up to 270 ind. m^-2). Species have been identified after morphological examination and corroborated by mitochondrial DNA sequence data: cytochrome c oxidase subunit 1 (COI) and cytochrome b (Cytb). Molecular data show that the same haplotypes have been found in distant and disjoint biogeographic areas worldwide, which is only explicable by unintentional translocation of specimens through vectors (i.e. ship hulls or ballast water). Species delimitation analyses support previous findings that species complexes are common in both Ficopomatus and Hydroides. In fact, only among the Majorcan samples were we able to detect three species of the F. enigmaticus species complex, two of the H. elegans species complex and two of the H. dianthus species complex. The genetic distances between members of the F. enigmaticus species complex are 8.7% to 16.7% in COI sequences. The species of Hydroides hold 5.4% to 47.6 % genetic divergence between species of the same complex.