Within the forest: a new species of Ctenomys (Rodentia: Ctenomyidae) from northwestern Patagonia.

This article focuses on the taxonomic and phylogenetic analysis of the genus *Ctenomys* in Patagonia, particularly describing a new species, *Ctenomys terraplen* sp. nov., from northwestern Chubut Province, Argentina. Using mitochondrial Cytochrome b DNA sequences and detailed morphological (skull and sperm) analyses, the study places *C. terraplen* within the magellanicus species group as sister to *C. magellanicus* (Magellanic Tuco-tuco), but distinct in genetic distance, morphology, and habitat preference, notably inhabiting temperate Valdivian forests rather than open steppes. The new species exhibits strong sexual dimorphism and differs morphologically from closely related and parapatric species such as *C. magellanicus*, *C. haigi*, and *C. plebiscitum*. The research also reports new locality records for *C. plebiscitum* and extends the known southern distribution of *C. haigi*, highlighting complex biogeographical patterns and underscoring the need for further taxonomic revision and conservation efforts within this diverse genus.