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Phreatobius cisternarum ZBK described by Goeldi (1905) is known only from relatively shallow wells at several localities near the mouth of the Amazon River (Carvalho 1967; de Pinna 1998; Muriel-Cuna & de Pinna 2005; Fig. 1). de Pinna (1998) mentioned the existence of two additional quite distinctive species, as yet undescribed, from the Río Negro of Brazil. Since its original description, Phreatobius ZBK remains monotypic and has been aligned with five different siluriform families (de Pinna 1998): Trichomycteridae, Cetopsidae, Clariidae, Plotosidae, and Pimelodidae (Heptapteridae). In the most recent treatment of species-level diversity of neotropical fishes, Phreatobius ZBK was assigned to the Heptapteridae (Bockmann & Guazzelli 2003). However, Muriel-Cunha and de Pinna (2005) and Ferraris (2007) suggest that the family-level placement of this genus and its single named species is unsettled. Superficial resemblance of Phreatobius ZBK to the African Clariidae and the exclusively marine Plotosidae is suggested by the elongate body and slender head, as well as by the rostrally extended caudal fin, continuous ventrally with the anal fin and reminiscent of the continuous fin configurations found in members of those families. A recent comprehensive synopsis of P. cisternarum ZBK was provided by Muriel-Cuna and de Pinna (2005), including observations on color, behavior, and feeding of eight living specimens held in captivity.
In this study, we report the first specimens of Phreatobius ZBK from Bolivia, which we recognize as a new species based on several unique features, most notable among them the absence of eyes. Specimens of Phreatobius sanguijuelan. sp. were collected from artificial wells that provide drinking water to the local community in the vicinity of Porvenir, northern Santa Cruz Department, within the RíoParaguá drainage basin. This species is endangered by environmental degradation due to pollution, water extraction for drinking and irrigation, mineral extraction, and associated erosion. The new species extends the geographical distribution of Phreatobius ZBK 2000 km to the west (Fig. 1), suggesting that members of the genus are likely to be much more widespread than previously recognized.