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[[ Genus Hypostomus Lacépède ZBK ]]
Hypostomus ZBK , the type genus of the subfamily Hypostominae, constitutes an assemblage of bottom-dwelling loricariid fishes widely distributed throughout South America, occurring in a variety of freshwater ecosystems such as small mountain streams and large lowland river areas. Maximum diversity in number of species of Hypostomus ZBK occurs in rivers of the Paraná-Paraguay system (Weber, 2003). As presently defined the genus consists of more than 130 nominal species (107 species considered valid by Weber, 2003 and expanded by Armbruster, 2004).
Species level taxonomy of Hypostomus ZBK is still poorly known as well as the phylogenetic relationships within and of the genus. Hypostomus ZBK was established by Lacépède (1803), who included in the genus only a single species, H. guacari ZBK . Old descriptions, similar to Lacépède ’s, and available for various subsequent species added to the genus, are very often scanty, with incomplete or poor characterization of species. This fact, together with a number of Hypostomus ZBK species yet to be described, makes the recognition of most taxa of the genus difficult. Hypothesis of phylogenetic relationships of Hypostomus ZBK based on molecular data (Montoya-Burgos et al., 1997, 2002) revealed that the genus does not form a natural group. According to these authors, some species currently assigned to Hypostomus ZBK should be removed from the genus, while the genus Cochliodon ZBK should be treated as synonym of Hypostomus ZBK , an action effectuated by Weber & Montoya-Burgos (2002: 265). Morphological based phylogenetic studies presented by Armbruster (2004) reinforce the conclusions above and place Aphanotorulus ZBK and Isorineloricaria ZBK in the synonymy of Hypostomus ZBK . In spite of the cited studies, more detailed phylogenetic analysis of the relationships within Hypostomus ZBK awaits for future studies.
The elevated number of species currently included in Hypostomus ZBK , allied to the broad variability in morphology and color pattern of those taxa, poses difficulties for its entire revision. Various authors acquainted with these problems provided regional revisions of the genus, as exemplified by Boeseman (1968) with a study of the Surinam representatives of the genus, Weber (1985, 1986, 1987) that deals with Hypostomus ZBK from Paraguay, more recently Reis et al. (1990) reviews and describes three new species from Southern Brazil, Mazzoni et al. (1994) provides a taxonomical revision of Hypostomus ZBK from Lower rio Paraíba do Sul, State of Rio de Janeiro, Brazil, and finally Hollanda Carvalho & Weber (2004) provided a revision of Hypostomus cochliodon group ZBK from middle and lower Amazon system.