Nannoptopoma, a new genus of loricariid catfishes (Siluriformes: Loricariidae) from the Amazon and Orinoco river basins

Nannoptopoma, new genus, is proposed for two species of diminutive loricariid catfishes of the subfamily Hypoptopomatinae. Nannoptopoma spectabilis (Eigenmann), a species originally placed in the genus Otocinclus Cope, is known from the upper Amazon and Orinoco basins of Peru, Ecuador, Colombia, and Venezuela and is designated the type species. Nannoptopoma sternoptychum, new species, is described from tributaries of the Amazon River in Ecuador, Brazil, and Peru and differs from its congener in terms of head shape, pectoral-fin length, and meristic features. Nannoptopoma is diagnosed among hypoptopomines by a number of osteological specializations. The new genus is most similar in external appearance to Hypoptopoma Gunther, yet lacks the pectoral spine serrae characteristic of the latter taxon. A sister group relationship with Hypoptopoma within the tribe Hypoptopomatini is supported by shared homologies of the jaw suspensorium, opercular series and cranium. A key is provided to the species of Nannoptopoma and to genera of the tribe Hypoptopomatini.