Zoologia porównawcza bezkręgowców

@article{Tratkiewicz2026,

title = {Molecular phylogeny of Catenulida (Platyhelminthes) with special focus on their diversity in Poland},

author = {Katarzyna Tratkiewicz and Jakub Baczyński and Ludwik Gąsiorowski},

doi = {10.1093/zoolinnean/zlag003},

issn = {1096-3642},

year  = {2026},

date = {2026-02-03},

urldate = {2026-02-03},

journal = {Zoological Journal of the Linnean Society},

volume = {206},

issue = {2},

publisher = {Oxford University Press (OUP)},

abstract = {Catenulida is a clade of free-living flatworms found abundantly in freshwater habitats across the globe. Despite their ubiquitous distribution, catenulids remain poorly studied; most of the species are known only from the asexual forms that lack distinct, taxonomically useful characters. Accordingly, the studies of catenulid diversity require application of integrative methods that combine morphological and molecular data. Here, we report a survey of catenulid diversity in Central and Western Europe, with a special focus on the species found in Polish freshwaters. We collected and identified 13 distinct morphotypes that were subsequently sequenced for four molecular markers—18S, 28S, COI, and ITS-5.8S. The obtained sequences, together with reference data from other catenulid species, were used to infer the comprehensive phylogeny of the clade. This analysis confirms the previous results on deep nodes of catenulid phylogeny, and also revealed several well-supported clades within the largest catenulid family Stenostomidae, each distinguished by unique combinations of morphological features. Moreover, based on our molecular and morphological data, we recognize Stenostomum heebuktense, as a younger synonym of Stenostomum gigerium and Catenula confusa, as a younger synonym of Catenula lemnae. We also highlight the major challenges in catenulid taxonomy, particularly the unresolved species complexes of Stenostomum leucops and Stenostomum simplex.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gąsiorowski2025b,

title = {Regeneration in the absence of canonical neoblasts in an early branching flatworm},

author = {Ludwik Gąsiorowski and Chew Chai and Andrei Rozanski and Gargi Purandare and Fruzsina Ficze and Athanasia Mizi and Bo Wang and Jochen C. Rink},

doi = {10.1038/s41467-024-54716-x},

issn = {2041-1723},

year  = {2025},

date = {2025-12-00},

urldate = {2025-12-00},

journal = {Nature Communications},

volume = {16},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {The remarkable regenerative abilities of flatworms are closely linked to neoblasts – adult pluripotent stem cells that are the only division-competent cell type outside of the reproductive system. Although the presence of neoblast-like cells and whole-body regeneration in other animals has led to the idea that these features may represent the ancestral metazoan state, the evolutionary origin of both remains unclear. Here we show that the catenulid Stenostomum brevipharyngium, a member of the earliest-branching flatworm lineage, lacks conventional neoblasts despite being capable of whole-body regeneration and asexual reproduction. Using a combination of single-nuclei transcriptomics, in situ gene expression analysis, and functional experiments, we find that cell divisions are not restricted to a single cell type and are associated with multiple fully differentiated somatic tissues. Furthermore, the cohort of germline multipotency genes, which are considered canonical neoblast markers, are not expressed in dividing cells, but in the germline instead, and we experimentally show that they are neither necessary for proliferation nor regeneration. Overall, our results challenge the notion that canonical neoblasts are necessary for flatworm regeneration and open up the possibility that neoblast-like cells may have evolved convergently in different animals, independent of their regenerative capacity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tratkiewicz2025b,

title = {Spontaneous ectopic head formation enables reversal of the body axis polarity in microscopic flatworms},

author = {Katarzyna Tratkiewicz and Ludwik Gąsiorowski},

doi = {10.1098/rspb.2025.1941},

issn = {1471-2954},

year  = {2025},

date = {2025-10-00},

urldate = {2025-10-00},

journal = {Proceedings of the Royal Society B: Biological Sciences},

volume = {292},

number = {20251941},

issue = {2057},

publisher = {The Royal Society},

abstract = {In most of the animals, the antero-posterior axis is specified during early embryogenesis. However, in the organisms that undergo somatic asexual reproduction, constant re-establishment of the body axis occurs during each asexual act in the context of the fully formed adult body. In microscopic flatworms from the genus Stenostomum the new head and tail structures are inserted in the pre-existing body plan during the asexual process known as paratomy. Here, we report a spontaneously occurring developmental error that results in the formation of worms with double heads at opposite ends of their bodies, lacking posterior pole identity. In the set of experiments, we show that the double-head phenotype is not heritable on the organismal level. Worms originating from the sectioning or fission of the double-head animals give rise to the healthy populations that do not display the erroneous asexual development. We also demonstrate that the piece of the worm with ectopic head can survive, regenerate the tail on its previously anterior pole and resume asexual reproduction. Effectively, such regeneration allows stable reversal of the body axis polarity without impairment of the survival or reproductive abilities of the animal, an exceptionally rare phenomenon among bilaterians.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gąsiorowski2025,

title = {Evidence for Multiple Independent Expansions of Fox Gene Families Within Flatworms},

author = {Ludwik Gąsiorowski},

doi = {10.1007/s00239-024-10226-4},

issn = {1432-1432},

year  = {2025},

date = {2025-01-18},

urldate = {2025-01-18},

journal = {Journal of Molecular Evolution},

volume = {93},

pages = {124-135},

publisher = {Springer Science and Business Media LLC},

abstract = {Expansion and losses of gene families are important drivers of molecular evolution. A recent survey of Fox genes in flatworms revealed that this superfamily of multifunctional transcription factors, present in all animals, underwent extensive losses and expansions during platyhelminth evolution. In this paper, I analyzed Fox gene complement in four additional species of platyhelminths, that represent early-branching lineages in the flatworm phylogeny: catenulids (Stenostomum brevipharyngium and Stenostomum leucops) and macrostomorphs (Macrostomum hystrix and Macrostomum cliftonense). Phylogenetic analysis of Fox genes from this expanded set of species provided evidence for multiple independent expansions of Fox gene families within flatworms. Notably, FoxG, a panbilaterian brain-patterning gene, appears to be the least susceptible to duplication, while FoxJ1, a conserved ciliogenesis factor, has undergone extensive expansion in various flatworm lineages. Analysis of the single-cell atlas of S. brevipharyngium, combined with RNA in situ hybridization, elucidated the tissue-specific expression of the selected Fox genes: FoxG is expressed in the brain, three of the Fox genes (FoxN2/3–2, FoxO4 and FoxP1) are expressed in the pharyngeal cells of likely glandular function, while one of the FoxQD paralogs is specifically expressed in the protonephridium. Overall, the evolution of Fox genes in flatworms appears to be characterized by an early contraction of the gene complement, followed by lineage-specific expansions that have enabled the co-option of newly evolved paralogs into novel physiological and developmental functions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gąsiorowski2023,

title = {Convergent evolution of the sensory pits in and within flatworms},

author = {Ludwik Gąsiorowski and Isabel Lucia Dittmann and Jeremias N. Brand and Torben Ruhwedel and Wiebke Möbius and Bernhard Egger and Jochen C. Rink},

doi = {10.1186/s12915-023-01768-y},

issn = {1741-7007},

year  = {2023},

date = {2023-12-00},

urldate = {2023-12-00},

journal = {BMC Biology},

volume = {21},

number = {1},

pages = {266},

publisher = {Springer Science and Business Media LLC},

abstract = {Background

Unlike most free-living platyhelminths, catenulids, the sister group to all remaining flatworms, do not have eyes. Instead, the most prominent sensory structures in their heads are statocysts or sensory pits. The latter, found in the family Stenostomidae, are concave depressions located laterally on the head that represent one of the taxonomically important traits of the family. In the past, the sensory pits of flatworms have been homologized with the cephalic organs of nemerteans, a clade that occupies a sister position to platyhelminths in some recent phylogenies. To test for this homology, we studied morphology and gene expression in the sensory pits of the catenulid Stenostomum brevipharyngium.



Results

We used confocal and electron microscopy to investigate the detailed morphology of the sensory pits, as well as their formation during regeneration and asexual reproduction. The most prevalent cell type within the organ is epidermally-derived neuron-like cells that have cell bodies embedded deeply in the brain lobes and long neurite-like processes extending to the bottom of the pit. Those elongated processes are adorned with extensive microvillar projections that fill up the cavity of the pit, but cilia are not associated with the sensory pit. We also studied the expression patterns of some of the transcription factors expressed in the nemertean cephalic organs during the development of the pits. Only a single gene, pax4/6, is expressed in both the cerebral organs of nemerteans and sensory pits of S. brevipharyngium, challenging the idea of their deep homology.



Conclusions

Since there is no morphological or molecular correspondence between the sensory pits of Stenostomum and the cerebral organs of nemerteans, we reject their homology. Interestingly, the major cell type contributing to the sensory pits of stenostomids shows ultrastructural similarities to the rhabdomeric photoreceptors of other flatworms and expresses ortholog of the gene pax4/6, the pan-bilaterian master regulator of eye development. We suggest that the sensory pits of stenostomids might have evolved from the ancestral rhabdomeric photoreceptors that lost their photosensitivity and evolved secondary function. The mapping of head sensory structures on plathelminth phylogeny indicates that sensory pit-like organs evolved many times independently in flatworms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}