The tadpole of Aparasphenodon brunoi is described and illustrated for the first time (external morphology and internal oral features) from Maricá, State of Rio de Janeiro, Brazil. Characters of this tadpole include: body representing 30% of total length; eyes lateral; spiracle single, sinistral, with opening directed upward and backward; anal tube median; dorsal fin originating at the mid-third of body; caudal tip extended into a flagellum; oral disc anteroventral; and labial tooth row formula 2(2)/6(1). In general, body and tail brown. Tail with transverse dark brown stripes. Morphological comparisons were made with tadpoles of eight other pond and stream-dwelling casque-headed treefrog species of the genera Argenteohyla, Osteocephalus, and Trachycephalus. The tadpoles of the subspecies of Argenteohyla possess characteristics that may indicate full specific rank of these taxa, so that the taxonomic status of these subspecies should be revaluated. Considering that high number of tooth rows is usually associated with stream dwellers, the presence of this characteristic in A. brunoi tadpoles (a pond-dweller) may represent retention of an ancestral lotic pattern. Furthermore, the number of tooth rows in the posterior labium of A. brunoi corroborates the putative morphological synapomorphy of the tribe Lophiohylini (presence of at least four posterior labial tooth rows in the larval oral disc).