Among the most interesting and poorly known groups of the South American fish fauna is the catfish trichomycterid subfamily Sarcoglanidinae that includes miniature psammophilic species. We herein describe a new species, Ammoglanis multidentatus sp. nov., with larger specimens reaching less than 20 mm of standard length. In contrast to other sarcoglanidines that are found in rivers draining rain-forests, this new species was collected in the Rio Paraguaçu basin, Brazilian semiarid Caatinga. Ammoglanis multidentatus differs from all other sarcoglanidines by some osteological features, comprising the presence of a ventral process on the sesamoid supraorbital in contact with the latero-posterior process of the autopalatine, a robust opercle with numerous odontodes, and a long anteroventral process of the opercle. The description of A. multidentatus expands the geographical range of Ammoglanis about 1000 km to east, which highly suggests that unknown species of Ammoglanis may occur in several other areas of South America, probably as a result of the absence of fish collections directed to sand habitats.

Biodiversity; Caatinga; Psammophily; Rio Paraguaçu basin; systematics