First record of Chaunus achavali (Anura, Bufonidae) from Rio Grande do Sul, Brazil, with a key for the identification of the species in the Chaunus marinus group

The bufonid toad Chaunus achavali, a recently described species known only from Uruguay, is recorded for Brazil. This species is morphologically similar to C. ictericus and C. arenarum, and several individuals were labeled in Brazilian scientific collections under these taxa. A lectotype of C. arenarum is designated. Additional field notes on C. achavali and a key for the identification of the species in the Chaunus marinus group are presented.