Is Hydroides brachyacanthus (Serpulidae, Annelida) a widely distributed species?

Hydroides brachyacanthus Rioja, 1941 (Serpulidae, Annelida), an important fouling species originally described from Southern Gulf of California, Mexico, has been reported from Mexican Pacific and numerous other tropical and... [ view full abstract ]

Hydroides brachyacanthus Rioja, 1941 (Serpulidae, Annelida), an important fouling species originally described from Southern Gulf of California, Mexico, has been reported from Mexican Pacific and numerous other tropical and subtropical localities. However, a recent description of H. amrii Sun et al., 2015, a species from southern Australia (NSW to SA) that was historically misidentified as H. brachyacanthus, suggested that the widely distributed nominal H. brachyacanthus is a complex of morphologically similar species. We compared fragments of 18S, ITS2, and cyt b DNA sequences of H. brachyacanthus sensu stricto from the type locality in Mexico with those of H. amrii from Australia. Our molecular data supported the morphology-based hypothesis of H. amrii and H. brachyacanthus sensu stricto as distinct species. However, the morphospecies H. amrii was represented by two well supported clades not recovered as sister taxa, one of which was instead closely related to tropical congeneric H. tuberculatus, but found only in St Vincent Gulf, South Australia. Whether the distribution of these two clades is a result of the combined effects of oceanic currents in southern Australia, human-driven introduction, or both, remains unknown. This study highlights the need for a global integrative approach when dealing with potentially invasive species easily translocated by human activities and calls for a revision of the entire H. brachyacanthus complex.