Descriptive morphology and phylogenetic relationships among species of the Neotropical annual killifish genera Nematolebias and Simpsonichthys (Cyprinodontiformes: Aplocheiloidei: Rivulidae)

Structures of the external morphology and skeleton of the annual fish genera Nematolebias and Simpsonichthys are described and illustrated. Phylogenetic relationships among all included species of both genera and other cynolebiatins are estimated, based on 116 morphological characters in a total of 50 terminal taxa. Nematolebias is hypothesized to be the sister group of a clade including Simpsonichthys, Austrolebias , Megalebias, and Cynolebias, which is diagnosed by ventral portion of mesopterygoid not overlapping quadrate, third neural spine approximately as wide as fourth neural spine, ventral condyle of coracoid narrow, scales slightly extending over anal-fin base, loss of vomerine teeth, loss of neuromast anterior to infraorbital series, ventral process of the angulo-articular short and narrow, and dorsal portion of cleithrum elongated. Simpsonichthys is divided into five subgenera, including Spectrolebias, previously considered a separate genus, Simpsonichthys, and three new subgenera, Xenurolebias, Ophthalmolebias, and Hypsolebias. Monophyly of Simpsonichthys is supported by a small pointed dorsal process on the palatine, unbranched fin rays on the tip of the dorsal and anal fins in males, and frontal Escales overlapped