First molecular phylogeny of the freshwater planarian genus Girardia (Platyhelminthes: Tricladida) unveils hidden taxonomic diversity and initiates resolution of its historical biogeography

The genus Girardia (Platyhelminthes: Tricladida) comprises several species of which some have spread from their original areas of distribution in the Americas to other parts of the globe. Due to great anatomical similarity between species, morphology-based phylogenetic analyses have struggled to resolve the affinities between species and species-groups. This problem is exacerbated by the fact that populations of Girardia may show only asexual reproduction by fissiparity and, thus, do not exhibit a copulatory apparatus, which hampers taxonomic identification of phylogenetic characters. In the present work, this problem has been resolved by constructing a molecular phylogeny of the genus. Although our samples do not include representatives of all known species, they cover a large part of the original distributional range of the genus Girardia. Our phylogenetic results suggest the presence of two main clades, which are genetically and karyologically highly differentiated. North and South American populations of G. tigrina actually constitute two sibling species that are not even closely related. The South American form is here described as a new species. The phylogenetic tree brings to light that Girardia arose on the South American portion of Gondwanaland, from which it, subsequently, dispersed to the Nearctic Region, probably more than once.

Current state of knowledge on freshwater planarians (Platyhelminthes, Tricladida, Dugesiidae) from Chile

The unique geography of Chile encompasses a wide diversity of ecosystems and a rich biodiversity. However, the platyhelminth fauna has been poorly studied. The aim of this work is to compile the historical record of freshwater planarians described for this country. We accessed worldwide databases and published articles to provide a comprehensive review of their discovery history, morphological characteristics and their localities. Freshwater planarians have been collected mainly in central and southern Chile, while in the northern region a single species has been described. The discovery of new species of freshwater triclads has the potential to reveal novel animal models to study regeneration and/or biological adaptations, as some species are suitable for culture in the laboratory. We discuss the many reasons why further research is needed for this animal group, which should include genomic and molecular genetic studies.