Description of a new species of Chaco Tullgren, 1905 (Araneae: Mygalomorphae: Pycnothelidae) from Argentina and the southernmost record of the genus

A new species of Chaco Tullgren, 1905 was discovered and is formally described. Chaco aoni sp. nov. from the Santa Cruz River in Santa Cruz Province, Argentina, is the southernmost recorded species of this genus. The new species is diagnosed on the basis of the morphology of the palpal organ and tibial apophysis of males and the shape of the spermathecae of females. A cladistic analysis was carried out based on an already published morphological matrix, which now also includes the new species. This new species is part of a monophyletic group including also Chaco tingua Indicatti, Folly-Ramos, Vargas, Lucas & Brescovit, 2015, C. tecka Goloboff, 1995, C. sanjuanina Goloboff, 1995, C. patagonica Goloboff, 1995 and C. ansilta Ferretti, 2014.