The phylogeny of Catenulida flatworms under the spotlight of our scientists

02 03 2026

Scientists from the Institute of Evolutionary Biology, Katarzyna Tratkiewicz, Dr Jakub Baczyński, and Dr Ludwik Gąsiorowski, have published research on the phylogeny of flatworms from the order Catenulida, with a special focus on Polish and European fauna. The article entitled “Molecular phylogeny of Catenulida (Platyhelminthes) with special focus on their diversity in Poland” was published in the Zoological Journal of the Linnean Society.

Free-living flatworms of the order Catenulida, despite their cosmopolitan distribution, are still poorly known in terms of taxonomy and the actual number of species. This is mainly because they often reproduce asexually, and their morphological features can be variable and difficult to interpret unambiguously.

The aim of the study was to investigate the diversity of Catenulida in Europe, to determine their phylogenetic relationships in detail based on both morphological and molecular data, and to organise the taxonomy of this group, including clarifying the position of the important model species Stenostomum brevipharyngium.

Material collected from numerous sites in Poland, Germany, the United Kingdom, and Italy, as well as from laboratories in the USA, enabled precise documentation of morphological traits and genetic analyses using molecular markers. The reconstruction of the phylogenetic tree made it possible to compare deeper evolutionary relationships and connections between closely related species within the genus Stenostomum. The analyses allowed the researchers to present the most comprehensive Catenulida phylogeny to date, which confirms earlier findings regarding the main branches of this group, while also organising relationships within the largest family, Stenostomidae.

The authors also demonstrated that species of the genus Stenostomum can be partly identified based on sets of morphological traits, such as the type of refractive bodies, the shape of the mouth opening, or a characteristic way of swimming. This strengthens the importance of an integrative approach in the taxonomy of these organisms. At the same time, the diversity of the Catenulida group occurring in Poland is still underestimated and requires further research. It seems that some species have wide geographic ranges, among others thanks to good dispersal abilities and asexual reproduction.

The phylogenetic position of the species S. brevipharyngium was also clarified, which is important for the further use of this species as a model organism in developmental and evolutionary studies. This publication is an important step towards a better understanding of a poorly studied but very interesting group of aquatic flatworms and shows how important it is to combine classical zoological observations with modern molecular methods in biodiversity research.

The research was funded by a NAWA Polish Returns grant “Elucidating ecological and developmental causes of asexual reproduction and colony formation in flatworms” led by Dr Ludwik Gąsiorowski

We warmly congratulate the authors on this interesting and wide-ranging study and wish them success in future projects!

Article link: https://doi.org/10.1093/zoolinnean/zlag003