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A solid basis to address the conservation challenges of amphibians requires an increased knowledge on their natural history and biology. Recent data on reproductive modes in amphibians suggest that they are much more complex and variable than previously thought but understudied. However, detailed information on the reproductive history is especially important to fill the current knowledge gaps. Following recent taxonomic changes in Ranitomeya variabilis, information about captive-breeding management, image-based measurements of total length and surface area of the silhouette for individuals from embryonic to metamorphic development, and detailed larval staging for captive-bred specimens are provided from French Guiana. The development of R. variabilis from the stage eight (Gosner 1960) through metamorphosis took 79 to 91 days (n = 6) with a survival rate of 46%. The developmental stages largely matched those of the generalized staging system of Gosner (1960), with differences in the stages when labia and teeth differentiation and atrophy of the oral apparatus occurred. Compared with other studies the total length of R. variabilis tadpoles was greater at given stages than those of R. variabilis from a Peruvian population and those of the sister species, R. amazonica. Other studies concerning growth curves based on surface area data revealed that R. variabilis tadpoles at peak size were larger than those of R. amazonica, R. imitator, R. reticulata, R. sirensis, and R. vanzolinii, but smaller than R. benedicta. Our results represent the first embryonic and larval staging for R. variabilis, and detailed information is provided on their initial life phases. These data may facilitate the identification of R. variabilis tadpoles in the wild, as well helping to clarify the biogeographical distribution and taxonomic arrangement of the species. In addition, knowledge is added to the captive-breeding methodology for the species.

In this study we morphologically examine larval specimens of Ranitomeya variabilis, which were breed in captivity and genetically determined to belong to the French Guiana population. We provide detailed data on the external morphology, chondrocranium, cranial muscle systems and inner organs of the tadpoles. Additionally, we provide essential characteristics for the recognition of the tadpoles of the different Ranitomeya species. The external morphology of the R. variabilis tadpoles was assessed by measurements and photographs of the specimens. Internal morphology was analysed using µCT images, µCT-based three dimensional reconstructions, and dissection of specimens for organ and muscle descriptions. The majority of the muscle configurations observed herein for larval specimens of R. variabilis are consistent with data presented in previous studies for larvae of other Ranitomeya species. In addition, several of the observed morphological characters are defined for different taxonomic levels within Dendrobatidae, e.g. the reduction of tectal cartilages and the insertion of the Muscular rectus cervicis on the third or fourth branchial arch. The absence of the anterolateral process of the ceratohyal in Ranitomeya and Dendrobates further strengthens their close relationship, in contrast to the more distantly related Epipedobates and Phyllobates where this structure is present. The absence of the musculi levator arcuum branchialium I and II, the musculus interhyoideus posterior and the musculus diaphragmatopraecordialis might be defining traits for Ranitomeya. Already a unique character observed in this study, is the fusion of the superficialis and profundus portion of the musculus levator longus for the R. variabilis larvae.