First Record of Pattersoniella vitiphila (Ciliophora, Hypotrichia) from Iguazú National Park, Argentina

Terrestrial ciliates are key components of soil ecosystems, contributing to microbial regulation and nutrient cycling, yet their diversity remains poorly known, particularly in South America. During biodiversity surveys in Iguazú National Park (Argentina), populations of the hypotrich genus Pattersoniella were discovered. This ciliate was previously recorded from the Fiji Islands, China, and Australia. In this context, the present study describes three further populations from Iguazú National Park, providing the first record of the genus in Argentina, expanding its known geographic distribution, and contributing to our understanding of the morphological variation of Pattersoniella vitiphila Foissner, 1987.

Bryophyte, lichen, and soil samples were collected along two visitors trails, the Lower and Upper Circuits, of Iguazú National Park in October 2017, July 2024 and June 2025. Morphological characterization and morphometric analyses were performed on living and protargol-impregnated specimens.

The populations recorded in Iguazú National Park generally agree with the morphological characteristics previously reported for the species. However, slight variations were observed in the number of cirri, macronuclear nodules, and, most notably, contractile vacuoles. The latter character appears to be variable among populations recorded from different regions of the world. In addition, giant morphs reaching up to 420 µm in vivo, were also observed in the bryophyte samples, as described for the Fiji populations.

The present study extends the known distribution of Pattersoniella vitiphila to South America, expanding the species distribution and improving current knowledge on its morphology. These results underscore the importance of further investigations of terrestrial ciliates in underexplored areas to better understand their diversity and distribution patterns.