Organisms Diversity & Evolution

, Volume 19, Issue 1, pp 41–62 | Cite as

Pseudovermis paradoxus 2.0—3D microanatomy and ultrastructure of a vermiform, meiofaunal nudibranch (Gastropoda, Heterobranchia)

  • Christina K. FlammensbeckEmail author
  • Gerhard Haszprunar
  • Tatiana Korshunova
  • Alexander V. Martynov
  • Timea P. Neusser
  • Katharina M. Jörger
Original Article


Pseudovermidae is the only clade of nudibranchs entirely comprised of mesopsammic species probably resulting from paedomorphosis. These minute slugs show a worldwide distribution with most lineages described from European waters. The present study redescribes the type species of Pseudovermidae, Pseudovermis paradoxus Pereyaslavtzeva, 1891, from the Black Sea with modern methodology. We provide computer-based 3D reconstructions of all organ systems and ultrastructural data on the digestive and renopericardial systems. Several aspects of the external morphology and the highly concentrated central nervous system in P. paradoxus are paedomorphic. The presence of a vestigial pericardium without a heart is interpreted as co-adaptation to the minute, vermiform body with a relatively large surface. The (partially) triaulic hermaphroditic genital system shows a small penis, suggesting true copulation as mode of sperm transfer. We provide a molecular barcode and a neotype in line with our detailed 3D microanatomy and ultrastructural data to establish a baseline for revision of Pseudovermidae. The current taxonomy of Pseudovermidae in European waters is likely artificially inflated, impeding a better understanding of distribution and diversification within the clade. Our study highlights the need for a taxonomic revision of European pseudovermid species based on molecular data, as traditional taxonomic characters mostly present a higher intraspecific rather than interspecific variation or might present artifacts (i.e., “denticulated” jaws).


Nudibranchia Meiofauna Morphology Paedomorphosis Progenesis Sea slug 



A special thanks to Julia Habel for collecting sand samples during her diving holidays in Crimea in 2009. Several people supported lab work of the present study: we wish to express our gratitude to Eva Lodde-Bensch (ZSM) for embedding the collected specimens and Martin Heß and Heidemarie Gensler (both LMU) for the technical assistance with ultrathin sectioning and transmission electron microscopy. Thanks also to Franziska Bergmeier (LMU) for the support using the software Amira® and feedback on the included artwork.


AM and TK were supported by a research grant of MSU Zoological Museum (АААА-А16-116021660077-3; depository of specimens) and in frame of Moscow University Project "Noah's Ark" (morphological and molecular study).


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Copyright information

© Gesellschaft für Biologische Systematik 2019

Authors and Affiliations

  • Christina K. Flammensbeck
    • 1
    Email author
  • Gerhard Haszprunar
    • 1
    • 2
  • Tatiana Korshunova
    • 3
    • 4
  • Alexander V. Martynov
    • 4
  • Timea P. Neusser
    • 1
    • 2
  • Katharina M. Jörger
    • 1
    • 2
  1. 1.Department Biology II and GeoBio-CenterLudwig-Maximilians-UniversityPlanegg-MartinsriedGermany
  2. 2.SNSB-Bavarian State Collection of ZoologyMunichGermany
  3. 3.Koltzov Institute of Developmental Biology RASMoscowRussia
  4. 4.Zoological MuseumMoscow State UniversityMoscowRussia

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