Biodiversity of freshwater planarians (Platyhelminthes, Tricladida, Dugesiidae) in Chile: exploration of unknown species.

backgroundFreshwater planarians (Tricladida) are widely used as model organisms in regeneration biology, invasion ecology, ecotoxicology, and systematics. Despite this relevance, their diversity remains poorly documented in large regions of South America. In Chile, only five freshwater planarian species have been formally described, a number that likely reflects limited sampling rather than true diversity. Given Chile’s pronounced latitudinal extent, biogeographic complexity, and environmental heterogeneity, freshwater planarian diversity is expected to be substantially underestimated. Here, we provide a first molecular-based assessment of Chilean freshwater planarians by sampling previously unexplored localities and integrating external morphology with phylogenetic and species delimitation analyses.

resultsSpecimens were collected from seven freshwater habitats spanning northern and central Chile, including high-altitude Altiplano environments and a geothermal field. External morphology was consistent with assignment to the genus Girardia, a conclusion supported by BLAST and BOLD searches. Phylogenetic analyses based on mitochondrial (COI) and nuclear (EF1-α) markers recovered three major Chilean clades with strong support, corresponding broadly to geographic regions. Altiplano populations formed a previously unreported monophyletic lineage within Girardia, suggesting isolation-driven diversification in extreme environments. Molecular species delimitation using ASAP, GMYC, and bPTP identified six putative species: Girardia sp. El Tatio, Girardia sp. Lauca/Chungará/Ascotán, Girardia sp. Calafquén, Girardia sp. OHP/LTB, Girardia sp. Los Lagos, and Girardia sp. LPM.

conclusionOur results reveal that freshwater planarian diversity in Chile is far greater than currently recognized and that Girardia exhibits pronounced geographic structuring across the country. The discovery of multiple genetically distinct lineages, including in high-altitude and geothermal environments, highlights the role of geographic isolation and environmental heterogeneity in shaping diversification. Although formal species descriptions will require internal anatomy and additional molecular data, this study provides a critical framework for future taxonomic, evolutionary, and ecological research on South American freshwater planarians and underscores the importance of expanding biodiversity surveys into understudied regions.