Extraocular muscles are classically grouped as four rectus and two oblique muscles. However, their description and potential associations with species behavior are limited. The objective was to characterize extraocular muscles in four Myliobatoidei rays from diverse habitats with divergent behaviors. Heads (10 per species) of Dasyatis hypostigma, Gymnura altavela, Mobula thurstoni and Pteroplatytrygon violacea were decalcified and dissected to characterize and describe extraocular muscles. Principal component analysis (PCA) was used to evaluate relationships between muscle length and species; for P. violacea, D. hypostigma and G. altavela, these were qualitatively and quantitatively consistent with the general pattern of extraocular muscles in vertebrates. In contrast, for M. thurstoni, the two oblique muscles were completely fused and there was a seventh extraocular muscle, named m. lateral rectus b (both were apparently novel findings in this species). There were also significant differences in eye disposition in the chondrocranium. The PCA axis 1 (rectus muscles) and PCA axis 2 (oblique muscles) accounted for 98.47% of data variability. Extraocular muscles had significant differences in length and important anatomical differences among sampled species that facilitated grouping species according to their life history. In conclusion, extraocular muscles are not uniform in all vertebrate species, thereby providing another basis for comparative studies.

We present data on the habitat, density, and spatial distribution of Rivulus giarettai, and discuss some biotic and abiotic variables related to its abundance in Free Flowing Waters (FFW) and Dam Reservoirs (DR) in palm grove (Mauritia flexuosa) marshes (Veredas) in Uberlândia, Minas Gerais, southeastern Brazil. The mean density (individuals/ plot) of R. giarettai was about 13 times higher in FFW than in DR. In FFW, the density of R. giarettai was highest at intermediate amounts of substrate (plant mass) and it was positively rank-correlated with the depth, and the number of arthropods. Individuals occurred in an aggregated distribution. The aggregated pattern could be related to a concentration of individuals in microhabitats neither too much exposed nor completely saturated by plants. R. giarettai was relatively abundant and tolerant to slight man-made habitat modifications. Damming appeared to be especially problematic by negatively affecting its density.

We describe a new species of Ischnocnema from the Cerrado (Brazilian savanna) of the Triângulo Mineiro region, state of Minas Gerais. Comparisons were made with those species historically thought to be closely related to I. juipoca. Topotype males (14.9–18.7 mm SVL) of the new species are smaller than those of Ischnocnema juipoca, I. octavioi, Eleutherodactylus heterodactylus, Pristimantis dundeei, and P. crepitans. Different from E. heterodactylus and P. crepitans, the new species does not have expanded discs on finger III and IV. The new species is different from P. dundeei by lacking finger/toe discs and nuptial pads. A marked sexual dimorphism in size is absent in P. crepitans and present in the new species. Different from the new species, I. verrucosa is coarsely tuberculate on dorsal surfaces. Ischnocnema verrucosa, I. octavioi, and P. dundeei are primarily forest dwellers while the new species is common in open areas. The advertisement call of the new species has more (1.5–2.5 times) pulses and higher (1.3–1.8 times) pulse repetition rate than that of I. juipoca.

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