A new species of killifish collected from the coastal plains of northeastern Brazil is so different from other killies that it's been placed in a new genus of its own.
The new fish, which was described by Wilson Costa in the journal Zootaxa, is believed to be in a sister group to the Rivulus genus.
Prorivulus auriferus sits within a monophyletic group with annual rivulid killifish, including the members of the Rivulus genus, as it shares two distinct features, called synapomorphies which are present in all of these fish - the absence of a second epibranchial and the presence of unossified interhyal and distal processes.
Unlike other rivulids, Prorivulus have five branchiostegal rays.
For more information on the description see the paper: Costa, WJEM (2004) - A new killifish genus and species from the coastal plains of north-eastern Brazil (Teleostei: Cyprinodontiformes: Rivulidae). Zootaxa 642: 1-10.