The family Rivulidae is the fourth most diverse clade of Neotropical fishes. Together with some genera of the related African family Nothobranchiidae, many rivulids exhibit a characteristic annual life cycle, with diapausing eggs and delayed embryonic development, which allows them to survive in the challenging seasonal ponds that they inhabit. Rivulidae also includes two species known as the only the self-fertilizing vertebrates and some species with internal fertilization. The first goal of this article is to review the systematics of the family considering phylogenetic relationships and synapomorphies of subfamilial clades, thus unifying information that is dispersed throughout the literature. From this revision, it is clear that phylogenetic relationships within Rivulidae are poorly resolved, especially in one of the large clades that compose it, the subfamily Rivulinae, where conflicting hypotheses of relationships of non-annual and annual genera are evident. The second goal of this work is to present an updated phylogenetic hypothesis (based on mitochondrial, nuclear, and morphological information) for one of the most speciose genus of Rivulidae, Austrolebias. Our results confirm the monophyly of the genus and of some subgeneric clades already diagnosed, but propose new relationships among them and their species composition, particularly in the subgenus Acrolebias.

The Hypsolebias antenori species group comprises a monophyletic clade of annual fishes occurring in the semi-arid region of Northeastern Brazil. Most species of this group are found in the Rio São Francisco basin, but there are three species that inhabit small coastal basins. Hypsolebias faouri new species, is described from a temporary pool located near Rio Preto, a tributary of the Rio São Francisco, and Hypsolebias martinsi new species, is described from an annual pool near Rio Icaraizinho, a coastal drainage. Molecular data corroborates the monophyly of Hypsolebias and both new species.

A new species of the genus Melanorivulus belonging to the Melanorivulus pictus species group is herein described, from a tributary of the Rio Grande, Rio Paraná basin, São Paulo State, Brazil. The new species can be distinguished from all other species of the Melanorivulus pictus species group by the unique presence of sides of body of males light bluish gray with 10–12 oblique red bars, 8 of which chevron-like, bifurcated and complete, i.e., running from dorsum to ventral area, and 2–4 incomplete, with vertices of the chevron-like bars along midbody, pointing forward. Comments on the putative relationships of the new species, as well as concerning its conservation status, are presented.

A new species of Simpsonichthys is described from the upper rio Jequitinhonha basin, Minas Gerais, eastern Brazil. It is diagnosed from all congeners by presenting an A-patterned frontal squamation. Additionally, males of the new species differs from all congeners by the color pattern of body, the color of iris, the absence of contact organs in the pectoral fin, presence of scales on anal-fin base, pectoral-fin length, caudal fin length, and eye diameter. Females of the new species can be diagnosed from remaining congeners by the pectoral-fin length. The conservation status of the new species is evaluated. Comments on the relationships of the new species within the genus Simpsonichthys are presented.

Simpsonichtys lopesi n. sp. is described from a temporary pool located in the São Francisco river basin. This species is distinguished from remaining species, except S. adornatus, by the large number of dorsal fin rays, which makes possible a large dorsal fin base length that begins well anterior to the middle of the body, before the vertical line through the pelvic fin. This species differs from S. adornatus by the color pattern of the anal fin, which may have yellow stripes or light dots (vs. small light points), and also by the lower number of dorsal fin rays. ResumoSimpsonichthys lopesi n. sp. é descrita de uma poça temporária localizada na bacia do rio São Francisco. A espécie distingue-se das demais, exceto S. adornatus, pelo grande número de raios da nadadeira dorsal, o que confere grande comprimento da base dessa nadadeira que se inicia muito antes da metade do corpo, antes da nadadeira pélvica. Difere de S. adonatus pelo padrão de colorido da nadadeira anal, que pode apresentar listras amareladas ou manchas claras (vs. pequenas pintas claras), e também pelo menor número de raios da nadadeira dorsal.