Integrative taxonomy reveals multiple Mediterranean invasions by Indo-Pacific Dorvillea (Annelida, Dorvilleidae)

Abstract

Biological invasions are a major driver of global biodiversity loss, with the Mediterranean Sea among the most heavily invaded marine regions. However, identification and monitoring of Non-Indigenous Species (NIS) are hindered by taxonomic uncertainty and cryptic diversity, especially in taxonomic groups whose complexity remains poorly explored, such as polychaete annelids. In this study, specimens morphologically identified as Dorvillea similis (Crossland, 1924) according to the current identification keys, were collected from the Mediterranean Sea, Red Sea, Arabian Gulf, and north-western Indian Ocean. Combined morphological and molecular analyses revealed eight distinct molecular operational taxonomic units (MOTUs), four of which are NIS in the Mediterranean. Five of these MOTUs (MOTUs 4–8) form a morphologically homogeneous group, designated here as the Dorvillea similis species complex. Two distinct lineages were shown to represent two new species, with one recently formalized as D. phoenicia Putignano et al. 2026 (MOTU 2), and another formally described herein as Dorvillea ariannae sp. nov. (MOTU 3). The MOTU 1 also belongs to a distinct but as yet unidentified Dorvillea sp. Although species previously identified as D. similis show a relatively homogeneous morphology of chaetae and jaw pieces, our results highlight the diagnostic value of both live colouration and arrangement of sub-epidermal glandular tissue for their distinction. This study further supports previous findings that marine annelid invasions in the Mediterranean Sea are currently underestimated and underscores the pivotal role of integrative taxonomy in improving our understanding of biological invasions.