Molecular phylogenetic position of a rare and enigmatic meiofaunal flatworm from the Pacific Ocean: Retronectes hyacinthe sp. nov. (Platyhelminthes: Catenulida)

Abstract

Catenulids comprise the earliest diverging major lineage of flatworms. Although the majority of catenulid species live in fresh water, a small number of taxa have been documented from marine interstitial environments and most of these belong to the genera Retronectes and Paracatenula within the family Retronectidae. Representatives of Retronectes are extremely uncommon and almost only found in detritus-rich sand, with the last formal description of a species of Retronectes dating back to 1977. Little is known about the biology of the seven known species in this genus despite the fact that a unique combination of characters makes them relatively straightforward to recognize. Moreover, previous molecular phylogenetic analyses have so far been unable to include any representatives of Retronectes, so the phylogenetic position of these rarely encountered marine catenulids remains unclear. Here we describe a new species of Retronectes, namely R. hyacinthe sp. nov., from subtidal seagrass meadows in British Columbia (Canada) and present an updated phylogeny inferred from 18S and 28S rDNA sequences, including data from the new species of Retronectes and a selection of other catenulids. Our molecular phylogenetic trees suggest that Retronectidae sensu Sterrer & Rieger, 1974 is not monophyletic, implying that the current taxonomic classification of the Catenulida and the importance of certain morphological characters on which this classification is based are in need of revision.

http://zoobank.org/urn:lsid:zoobank.org:pub:A38635FB-7A8A-4C11-B513-BDBF9EA780CB

Key Words:

• British Columbia
• Catenulida
• Paracatenula
• Retronectidae
• seagrass
• Turbellaria

Acknowledgements

We are very grateful to all the staff at the Hakai Institute for making the fieldwork possible. Eunji Park, Danja Currie-Olsen and Regine Claire Manglicmot were also of great assistance during the field trip.

Disclosure statement

The authors have no conflict of interest to declare that is relevant to the content of this article.

Availability of data and material

GenBank accession numbers of the sequences generated for this study are included in the Supplemental Material.

Authors’ contributions

Conceptualization: NWLVS, BSL; Methodology: NWLVS, AC, TF; Formal analysis and investigation: NWLVS; Writing – original draft preparation: NWLVS, BSL; Writing – review and editing: NWLVS, BSL; Funding acquisition: BSL; Resources: AC, TF, BSL; Supervision: BSL

Sampling

The fieldwork was covered under a DFO collection permit XR 195 2022.

Supplemental data

Supplemental material for this article can be accessed here: https://dx.doi.org/10.1080/14772000.2023.2221236.

Associate Editor: Dr Jesús S. Hernández-Orts

Additional information

Funding

This work was funded by the Tula Foundation’s Hakai Institute and the Natural Sciences and Engineering Research Council of Canada (NSERC 2019-03986).