Plesiolebiasini Costa

Wilson J. E. M. Costa, 2007, Taxonomy of the plesiolebiasine killifish genera Pituna, Plesiolebias and Maratecoara (Teleostei: Cyprinodontiformes: Rivulidae), with descriptions of nine new species., Zootaxa 1410, pp. 1-41 : 2-3

[[ Tribe Plesiolebiasini Costa ]]

The Plesiolebiasini (sens. Costa, 2004) is a well corroborated clade of Neotropical seasonal killifishes, whose recognition is supported both by morphological (Costa, 1998a) and genetic data (Murphy et al, 1999; Hrbek & Larson, 1999). It includes the following genera (number of valid species according to Costa, 2003, appear in parentheses): Maratecoara Costa (2), Papiliolebias Costa (1), Pituna Costa (2), Plesiolebias Costa (4), and Stenolebias Costa (2). Species of Pituna , Plesiolebias and Maratecoara are often found in the same biotopes in the Araguaia and Tocantins river basins, but Pituna also occurs in the rio Paranaíba basin and Plesiolebias is in the rio Paraguay basin. Pituna and Plesiolebias are also present in the rio Xingu basin (e. g., Costa, 1998a, 1998b, 2003; present paper). The remaining two plesiolebiasine genera, Papiliolebias and Stenolebias , are endemic to the rio Paraguay basin, in the Chaco (Paraguay, Bolivia and Argentina) and the Brazilian Pantanal, respectively (e. g., Costa, 2003).

Plesiolebiasines are seasonal fishes, inhabiting temporary freshwater biotopes formed during the rainy season (October-April) and which are completely dry during part of the year (June-September). In southern Amazonian tributaries, plesiolebiasines exhibit a noteworthy evolutionary radiation, involving both morphological and ecological features. Species of Pituna are slender, usually found only in the peripheral shallowest parts of pools, about 100 mm deep or less. Plesiolebias comprises small species, in which the maximum adult size often does not surpass 20 mm SL, and typically lives in mid-water, usually close to aquatic vegetation.

Maratecoara includes deep-bodied species, in which males have long unpaired fins and anterodorsal trunk profile strongly convex. It is collected near the bottom of pools (Costa, 1998a).

Pituna was first erected to include a single species, P. poranga Costa , from the rio Araguaia basin, central Brazil (Costa, 1989a). Subsequently, Costa (1991a) examined the type specimens of Rivulus compactus Myers , from the rio Tocantins basin (also in central Brazil), and reported that they were similar to P. poranga . He consequently transferred R. compactus to Pituna . However, Costa (1991a) did not provide characters for distinguishing P. compacta and P. poranga , due to the poor condition of the three small female specimens in the type series of P. compacta , but noted that females of P. compacta have isolated spots on the flanks, while females of P. poranga have flank spots fused to form a distinct color pattern.

Additional collections of Pituna were made from the Araguaia-Tocantins River basin, making possible a first revision of the genus, which included, for the first time, data on osteology and frontal squamation pattern (Costa, 1998b). However, based upon similarities of most morphological features (except for significant variation of female color patterns among different populations), Costa (1998b) considered P. poranga to be a synonym of P. compacta , and Pituna thus a monotypic genus.

Plesiolebias Costa includes four valid species: P. aruana (Lazara) , from the rio Araguaia basin; P. glaucopterus (Costa & Lacerda) , from the rio Paraguay basin; P. lacerdai Costa , from the rio das Mortes floodplains; and P. xavantei (Costa, Lacerda & Tanizaki) , from the rio Tocantins basin (Costa, 1998c). All species were described after 1986, and the genus was recently revised (Costa, 1998c). In this revision, the geographic distributions of some species were expanded, based on samples containing small, poorly preserved specimens. For example, P. lacerdai , first known only from the rio das Mortes floodplains, was recorded from an area of the middle rio Araguaia basin near ilha do Bananal; and P. aruana , previously known from localities along the rio Araguaia floodplains, was recorded from the middle rio Tocantins basin.

Maratecoara comprises M. lacortei (Lazara) , from the middle rio Araguaia basin, and M. formosa Costa & Brasil , from the rio Tocantins basin (Costa, 1995a). Both species were known from few specimens and available descriptions are limited (Lazara, 1991; Costa, 1995a, 1995b).

Recent additional collections from poorly sampled areas, examination of live and preserved fully-developed adult specimens (not available in previous studies), and the study of new morphological characters provide an opportunity to further clarify the systematics of the genera Pituna , Plesiolebias and Maratecoara , as presented here.