Morphological and molecular investigation of <i>Scolelepis agilis</i> (Verrill, 1873) (Annelida: Spionidae) from beaches of the Atlantic coast of North America

Polychaete worms of the genus <i>Scolelepis</i> are one of the most abundant members of beach ecosystems worldwide. Along the Atlantic coast of North America, specimens of <i>Scolelepis</i> inhabiting high-energy beaches have long been erroneously identified as the European species <i>Scolelepis squamata</i> (O.F. Müller, 1806). In this study, we examined specimens of <i>Scolelepis</i> collected from Massachusetts to Virginia, finding they match <i>Scolelepis agilis</i> (Verrill, 1873), originally described from beaches in New Jersey. <i>Scolelepis agilis</i> can be most easily distinguished from <i>S. squamata</i> based on differences in palp ciliary pattern, morphology of neuropodial lamellae, and the quantity and start of both notopodial and neuropodial hooded hooks. Live specimens of <i>S. agilis</i> collected from New York were also examined to provide data on their reproduction and morphometric analyses. In addition, molecular data (18S, 28S rRNA, cytochrome c oxidase I and 16S rRNA) showed that specimens of <i>S. agilis</i> from the north to mid-Atlantic coast formed a monophyletic group (<i>p</i>-distance ≤ 0.004 for MA, RI, NY and VA populations) and were distinct from <i>S. squamata</i> (<i>p</i>-distance ≥ 0.196 (0.03 SE)). The molecular data also suggest the presence of several misidentified or undescribed species of <i>Scolelepis</i>, highlighting the need for additional taxonomic work on the genus from these localities as well as others (e.g. South Africa) where the worms have been incorrectly identified as <i>S. squamata</i>. A key to species of <i>Scolelepis</i> from the east coast of the United States is provided and a lectotype and paralectotypes for <i>S. agilis</i> are herein designated.