Acoustical parameters and/or tadpoles morphology together with the adult morphology have been used to resolve taxonomic problems in anuran amphibians. So, the knowledge of the larval morphology and of the behavioral and ecological aspects are important components as well as the traditional morphology analysis. Herein, we described the vocalizations and the tadpole (external morphology and internal oral features) of Leptodactylus spixi Heyer, 1983, species that belongs to the Leptodactylus fuscus group. The advertisement call is a harmonic single note, not pulsed, with a mean duration of 120ms, mean repetition rate of 90 calls/min, and an ascendant frequency modulation ranging from 522 to 2033Hz. The dominant frequency corresponds to the fundamental one, presenting a mean value of 1634Hz. All advertisement calls of the species of the L. fuscus group present an ascendant frequency modulation. We identified three different patterns of advertisement call in this group: pulsed calls, a weak modulation whistle, and a strong modulation whistle. The aggressive call is formed by a series of pulsed notes with harmonic structure. Each note presents median duration of 1317ms and dominant frequency of 1445.7Hz, that corresponds to the second harmonic. The tadpole of L. spixi is very similar in morphology, color, and internal oral features (number and structures of bucal floor and roof) when compared to the other tadpoles of the L. fuscus group. The labial tooth row of the tadpole of L. spixi is 2(2)/3.
