Laelapid mites (Parasitiformes: Gamasida), parasites of Akodon philipmyersi (Rodentia: Cricetidae) in the Northern Campos Grasslands, Argentina, with the description of a new species.

Androlaelaps ulysespardinasi, a new species of laelapid mite, is described based on specimens collected from the pelage of the akodontine rodent Akodon philipmyersi Pardiñas, D'Elía, Cirignoli and Suarez, 2005, which is endemic to the Northern Campos Grasslands in Misiones Province, Argentina. The formal taxonomic description, illustrations, and scanning electron micrographs of the new species are derived from female specimens; males and nymphs are unknown. Androlaelaps ulysespardinasi resembles Androlaelaps rotundus Fonseca, 1936 in general appearance, but it differs in having a more sclerotized, V-shaped and elevated ridge among j4 and j6 setae in the dorsal shield; the idiosoma is smaller (586-634 µm in length) and has a bilobed posterior margin. The sternal plate is 1.3 times broader than longer, the epigynial shield is 1.2 longer than broader, and an anal shield is almost as long as it is broad. Both species are close to Androlaelaps misionalis Lareschi, 2010 and Androlaelaps maurii Lareschi and Gettinger, 2009, but they differ in their larger size (586-650 µm), in having the distance between j6 setae similar to the distance between j5 setae (72-83 µm), 11 pairs of setae in opisthogaster, and lacking a pair of setae close to epigynal shield. In addition, An. ulysespardinasi n. sp. is unusual in having chelicerae with both digits with 2 teeth. An An. rotundus species group, which includes the new species, is proposed, and a key to identify the different species is provided. Host specificity of the different species with rodents from the Akodon division of the akodontines was observed, suggesting that cophylogeny between these mites and akodontines may have occurred.