Reappraisal of the hyperdiverse Platynereis dumerilii (Annelida: Nereididae) species complex in the Northern Atlantic, with the description of two new species

Morphologically similar species are often overlooked but molecular techniques have been effective in signalling potential hidden diversity, boosting the documentation of unique evolutionary lineages and ecological diversity. Platynereis dumerilii and Platynereis massiliensis are part of a recognised species complex, where differences in the reproductive biology have mainly been highlighted to date. Analyses of DNA sequence data (COI, 16S rDNA and D2 region of the 28S rDNA) of populations of the apparent morphotype of P. dumerilii obtained from a broader sampling area along European marine waters, including the Azores and Webbnesia islands (Madeira and Canaries), provided compelling evidence for the existence of at least 10 divergent evolutionary lineages. Complementing the genetic data, morphological observations of the better represented lineages revealed two major groups with distinctive paragnath patterns. Two new Platynereis species were erected: P. nunezi sp. nov., widespread in the Azores and Webbnesia islands, and P. jourdei sp. nov., restricted to the western Mediterranean. The new combination P. agilis is also proposed for Nereis agilis, previously unaccepted for one of the lineages present both in the Northeast Atlantic and western Mediterranean. Platynereis dumerilii is redescribed based on topotypic material. However, uncertainty in the identity of P. massiliensis due to the original brief description and the absence of type and topotypic material prevents the unequivocal assignment to the lineage assumed in this and previous studies. The remaining five lineages are represented by only a few small specimens with morphological features poorly preserved and were therefore not described in this study.

This study was supported by the project Next generation monitoring of coastal ecosystems in a scenario of global change (NextSea, NORTE-01-0145-FEDER-000032), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). Thanks are due, for the financial support of CESAM – Centro de Estudos do Ambiente e do Mar (UIDB/50017/2020+UIDP/50017/2020), to Portuguese Foundation for Science and Technology and Ministry of Education and Science (FCT/MEC) through national funds, and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. The research leading to these results also received partial funding, from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730984, ASSEMBLE Plus project (application n. 8229, 4th CALL, "Crypticism in the marine realm: DNA barcode-based outlook into selected invertebrate taxa of the Eastern Mediterranean"). Marcos AL Teixeira was supported by a PhD grant from FCT co-financed by ESF (SFRH/BD/131527/2017) and from the DNAqua-Net STSM grant "Rich and hidden biodiversity not yet barcoded in the Canary archipelago (Spain) as an opportunity to enrich the DNA barcode reference library for European polychaetes", under the EU Cost action CA15219 - Developing new genetic tools for bioassessment of aquatic ecosystems in Europe. Pedro Vieira work was supported by national funds through the Portuguese Foundation for Science and Technology (FCT, I.P.) in the scope of the project (Early detection and monitoring of non-indigenous species in coastal ecosystems based on high-throughput sequencing tools, PTDC/BIA-BMA/29754/2017). Ascensão Ravara was funded by national funds, through FCT, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. Financial support to Arne Nygren from the Norwegian Taxonomy Initiative [http://www.biodiversity.no/Pages/135523] (Cryptic polychaete species in Norwegian waters, knr 49-13, pnr 70184228), the Swedish Taxonomy Initiative [https://www.artdatabanken.se/en/the-swedish-taxonomy-initiative/] (Polychaete species complexes in Swedish waters, dnr 140/07 1.4 and 166/08 1.4), and Kungliga Fysiografiska sällskapet Nilsson-Ehle donationerna [https://www.fysiografen.se/sv/]. Financial support to Torkild Bakken from the Norwegian Taxonomy Initiative project Polychaetes in Norwegian Ports project no. 70184238.