Gymnotocinclus, new genus

Type species: Gymnotocinclus anosteos, by original designation (Fig. 1).

Diagnosis. Gymnotocinclus is distinguished from all other hypoptopomatine genera by the following uniquely derived features: (1) extreme reduction of body dermal plates (Fig. 2), (2) absence of the lateral connecting bone, (3) absence of bifid hemal spines on the abdominal vertebrae posterior to the first anal-fin proximal radial (Fig. 3), and (4) odontode tips on last dermal plates on the caudal peduncle dorsally or anteriorly curved (Fig. 4). Gymnotocinclus is also distinguished by a number of non-exclusive traits: maxillary barbel adnate to the lower lip; lateral ethmoid almost completely encapsulating the nasal organ (Fig. 5); ventral margin of preopercle straight, not deflected medially; pectoral girdle exposed and supporting odontodes only in a restricted lateral area near base of pectoral fin (Fig. 6); and absence of a pectoral-fin slit.

Etymology. From the Greek Gymnos, naked, and Otocinclus, a genus of the Hypoptopomatinae, in allusion to the extreme reduction of the body encasing dermal plates.