Abstract:

Spectrolebias semiocellatus, new genus and species, is described from the rio Formoso drainage, rio Araguaia basin, entral Brazil. It differs from all other taxa of the family Rivulidae in having a translucent body, a posteriorly xpanded swimbladder, an elongate black spot anteriorly bordered by a bright blue spot on the distal margin of nal fin of male, a dark transverse stripe on posterior portion of eye, a very narrow body, and all dorsal, anal and )elvic-fin rays unbranched. It is placed in the subtribe Cynolebiatina by the possession of anal fin positioned nteriorly and sexual dimorphism in number of dorsal and anal-fin rays, and it is hypothesized to be the sister ;roup to a clade comprising the other genera of Cynolebiatina (Cynolebias, Simpsonichthys) by presenting the 'lesiomorphic condition for posterior process of quadrate length and the absence of black spots on center of body ides of juvenile and adult female.

Spectrolebias was erected in the description of Spectrolebias semiocellatus Costa & Nielsen, 1997. This monotypic genus was hypothesized to be the sister-group of (Cynolebias + Simpsonichthys). The species group was named Spectrolebiatina, which was subsequently corrected to  Spectrolebiina (Huber 2005).
In Costa's (2006) revision of some Rivulids, Spectrolebias was relegated to a subgenus of Simpsonichthys. Four other species formerly placed in Simpsonichthys were moved to this subgenus: S. reticulatus, S. costai, S. chacoensis and S. filamentosus. In September 2008 Simpsonichthys inaequipinnatus was included in this group. More recently, Spectrolebias  was elevated to generic status again (Costa, 2011).

Behavior:

This species group prefers to live in larger bodies of stagnant water that can be of a temporary nature such as swamps, flooded land and pools. They can be found in savannah- and forest-like areas, mostly over mud. General behavior is like that of most Simpsonichthys spp., as they like to dwell in small groups and are not very active: not fast swimming, rather peaceful, standing in shaded places. They eat, as most other annuals do, mosquito larvae and small flying insects or crustaceans.

Costa (2006) described the distribution of Spectrolebias as southern Amazonian river drainages, including Rio Madeira, Xingu, Araguaia and Tocantins, and Paraguayan Chaco, Río Paraguay basin.

Literature: Costa, W. J. E. M. 2010. Historical biogeography of cynolebiasine annual killifishes inferred from dispersal- vicariance analysis. Journal of Biogeography, 37: 1995-2004.

Ponzetto Josi M., Ricardo Britzke, Dalton T. B. Nielsen, Patricia P. Parise-Maltempi& Anderson L. Alves. 2016. Phylogenetic relationships of Simpsonichthys subgenera (Cyprinodontiformes, Rivulidae), including a proposal for a new genus. Zoologica Scripta, The Royal Swedish Acedemy of scienses.