Rachovia stellifer killifish placed in new Llanolebias genus

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A new genus has been erected for the South American annual killifish species Rachovia stellifer based on morphological and molecular evidence.

Publishing their results in a recent issue of the journal Zootaxa, Tomas Hrbek and Donald Taphorn erected the new genus Llanolebias for Rachovia stellifer based on the results of a phylogenetic analysis of 19 rivulid species using 3635 molecular (representing 12 mitochondrial and nuclear genes) and 93 morphological characters.

Based on the results of this analysis, the authors concluded that Rachovia stellifer (originally described as Rivulus stellifer) should be placed in its own genus. Llanolebias is named after the Spanish Llanos (grassy plains, and in particular the Orinoco River savannahs of Venezuela and Colombia) and the Greek Lebia (a small fish and a nominal cyprinodontiform genus).

The authors write Llanolebias is diagnosed by the numerous molecular characters, however, it possesses no unique morphological characters that will unambiguously distinguish it from all other rivulid species; however, 13 characters distinguishing it from the genus Rachovia, and 33 characters distinguish it from the genus Gnatholebias. Compared to its sister genus Gnatholebias, the single species of Llanolebias is a robust, cylindrical-shaped fish, with short fins and in males very small fin-ray extensions, while Gnatholebias species have relatively deep, laterally compressed bodies with long fins and long fin-ray extensions.

The anal fin base of Llanolebias is also short compared to species of Gnatholebias, and Llanolebias has 14-15 anal fin rays versus22-26 fin rays in Gnatholebias. Llanolebias also lacks the fatty predorsal ridge characteristic of older males of Rachovia.

With the sole exception of females of Renova oscari, Llanolebias is the only member of the ~lowland annual clade of Rivulidae with a ~Rivulus spot in females.

Llanolebias stellifer also differs ecologically from the two species of Gnatholebias. Llanolebias stellifer occurs in shallow habitats on the edges of aquatic systems in deep forest, whilst Gnatholebias zonatus is from sunny pools in the savannah and Gnatholebias hoignei is from shaded but deeper pools than L. stellifer.

Llanolebias stellifer is confined to seasonally wet areas in the seasonally dry tropical forest region of the Llanos, and is found in a habitat similar to that occupied by species of the genera Aphyolebias and Moema which are found in seasonally wet areas of dense tropical forests of the Amazon and Essequibo basin.

For more information, see the paper: Hrbek, T and DC Taphorn (2008) Description of a new annual rivulid killifish genus from Venezuela. Zootaxa 1734, pp. 27"42.