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The molecular phylogenetic position of Mariplanella piscadera sp. nov. reveals a new major group of rhabdocoel flatworms: Mariplanellida status novus (Platyhelminthes: Rhabdocoela)


Rhabdocoels comprise a large group of flatworms that currently consists of two major subgroups: (1) Kalyptorhynchia with an anterior proboscis and (2) Dalytyphloplanida without a proboscis. Most genera of rhabdocoels can easily be classified into one of these two subgroups, except for the three monotypic representatives of the Mariplanellinae. Comparative morphological data and previous molecular phylogenetic analyses have so far been unable to determine the positions of these rarely encountered microturbellarians within the context of rhabdocoels. Here we describe a new species of Mariplanellinae, Mariplanella piscadera sp. nov. from Curaçao (Dutch Caribbean), and present an updated phylogeny inferred from 18S and 28S rDNA sequences, including data from M. piscadera sp. nov., M. frisia, and a selection of rhabdocoels, proseriates and other trepaxonematan flatworms. Our molecular phylogenetic trees reveal that Mariplanella belongs to a distinct higher-level group of rhabdocoels that forms the sister lineage to a clade uniting Kalyptorhynchia and Dalytyphloplanida. Therefore, we update the status of Mariplanellinae to Mariplanellida status novus, containing the family Mariplanellidae status novus, in order to better reflect our current understanding of rhabdocoel phylogeny and the establishment of now three major subgroups.

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The sequence alignments and molecular phylogenetic trees of this study are available in Mendeley Data, V1, GenBank accession numbers of the sequences generated for this study are included in Table S2.


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We are grateful to the Caribbean Research and Management of Biodiversity Institute (CARMABI) and their helpful staff for supporting the sampling campaign in Curaçao. We also like to thank two anonymous reviewers for their valuable suggestions to improve this work.


This work was funded by the Canadian Institute for Advanced Research (CIFAR), the Tula Foundation’s Hakai Institute and the National Sciences and Engineering Research Council of Canada (NSERC 2019–03986).

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NWLVS and BSL took part in conceptualization; NWLVS involved in methodology; NWLVS took part in formal analysis and investigation; NWLVS and BSL involved in writing—original draft preparation; NWLVS and BSL took part in writing—review and editing; BSL involved in funding acquisition; BSL took part in resources; BSL took part in supervision.

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Correspondence to Niels W. L. Van Steenkiste.

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No approval of research ethics committees was required because the work was conducted with unregulated invertebrate species.

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Van Steenkiste, N.W.L., Leander, B.S. The molecular phylogenetic position of Mariplanella piscadera sp. nov. reveals a new major group of rhabdocoel flatworms: Mariplanellida status novus (Platyhelminthes: Rhabdocoela). Org Divers Evol 22, 577–584 (2022).

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  • Microturbellaria
  • Mariplanellinae
  • Meiofauna
  • Phylogeny
  • Curaçao
  • Caribbean