The oral apparatus of anuran tadpoles is a unique structure composed of soft and keratinized parts surrounding the mouth. Among the many variations, a common oral apparatus involves a dorsal gap in the marginal papillae, keratinized jaw sheaths, and two upper and three lower rows of labial teeth. In Leiuperidae, besides this generalized morphology, four configurations are distinguished by the arrangement of the lower marginal papillae and the number of lower tooth rows. Study of the early oral ontogeny in 12 species representing these five configurations shows variations in the development of the lower marginal papillae and the third lower labial tooth row. Similar configurations may result from similar pathways (e.g. Physalaemus cuvieri group and Pseudopaludicola falcipes) or different pathways (e.g. generalized oral discs of Pleurodema and Physalaemus). Different oral configurations may result from overlapping trajectories ending at different stages (e.g. Physalaemus riograndensis and Ph. biligonigerus) or different trajectories (e.g. Ph. henselii and Ph. gracilis). Further studies are needed to interpret the role that heterochrony has played in evolutionary change within this family. The unsuspected variation occurring in this transient structure highlights its evolutionary potential and might be insightful in studies of anuran phylogenies that are largely based on adult characters.

We present a comprehensive review of larval morphology in the Neotropical toad genus Melanophryniscus. The taxa studied included 23 species with representatives of recognized phenetic groups and different larval ecomorphological guilds: pond, stream, and phytotelm-dwelling tadpoles. Their external morphology variation is congruent with current phenetic arrangement based on adult features, but also reflects the habitat where larvae develop. Lotic tadpoles (i.e. M. tumifrons group and M. krauczuki) in general exhibit a more depressed body, a longer tail with lower fins, and larger oral discs than lentic forms (i.e. M. stelzneri group, M. moreirae, *Corresponding author. E-mail: diegobaldo@gmail.com M. sanmartini, and M. langonei).Despite their peculiar, confined microhabitat, phytotelm larvae do not diverge markedly from non-arboreal species. The distinctive features of all species are the presence of a pineal end organ and the placement of the intestinal reversal point at the left of the abdomen in typical larval stages. The buccal cavity and musculoskeletal anatomy are quite conserved between species, yet some characteristics differ from those of other bufonids. The presence of one pair of subhyoid muscles is apparently an exclusive trait of Melanophryniscus among Bufonidae.

The bufonid genus Melanophryniscus includes 26 species that are divided into three phenetic groups based on adult morphology. Larvae develop in environments such as temporary ponds, streams or phytotelms. We studied variation in external morphology related to lentic and lotic microhabitats, through landmark-based geometric morphometrics on body shape, and multivariate analysis on oral disc measurements. Results show a morphological continuum between species that inhabit lentic versus lotic water systems. Features both in body shape and oral disc coincide with previous characterizations of lentic and lotic tadpoles published elsewhere.El género de bufónidos Melanophryniscus comprende 26 especies actualmente reunidas en tres grupos fenéticos distinguidos por la morfología de los adultos. En adición, las larvas se desarrollan alternativamente en variados ambientes, tales como charcos, arroyos temporarios y fitotelmata. Estudiamos la variación morfológica externa asociada a ambientes lóticos y lénticos, mediante morfometría geométrica de landmarks sobre la forma del cuerpo, y análisis multivariado de las medidas del disco oral. Los resultados muestran un continuo morfológico entre las especies que habitan sistemas lénticos vs. lóticos. Las características corporales y del disco oral coinciden con caracterizaciones previas de renacuajos lénticos y lóticos ya publicadas.