We describe the external morphology, buccal cavity, chondrocranium, hyobranchial skeleton, and musculature of the tadpole of Rhinella achavali (Achaval's Toad), along with its karyotype. Tadpoles were found in a small, permanent stream and were showing schooling behavior. The characterization of the proposed species groups within Rhinella cannot be currently improved using external larval morphology, as it seems to be much conserved within this genus. Buccal cavity morphology confirms the distinctiveness of the Rhinella veraguensis (Veragua Toad) group with respect to other known Rhinella. Musculoskeletal character states are similar among bufonids, although within this family the basal genus Melanophryniscus shows some distinctive states. The karyotype is composed of 22 bi-armed chromosomes, with secondary constrictions in pair 7, as found in the other species in the Rhinella marina (Marine Toad) group.