Gymnotocinclus, Carvalho & A. & Reis, 2008

Carvalho, Tiago Pinto, A., Pablo Lehmann & Reis, Roberto E., 2008, Gymnotocinclus anosteos, a new uniquely-plated genus and species of loricariid catfish (Teleostei: Siluriformes) from the upper rio Tocantins basin, central Brazil, Neotropical Ichthyology 6 (3), pp. 329-338 : 330

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.

Figures

Fig. 1. Gymnotocinclus anosteos, holotype, MCN 18624, male, 44.3 mm SL, ribeirão das Cobras, near highway GO-327, tributary of rio Tocantinzinho, rio Tocantins Basin, Alto Paraíso de Goiás, Goiás, Brazil.

Fig. 2. Gymnotocinclus anosteos, cleared and stained paratype, MCP 41726, male, 40.5 mm SL, collected with the holotype.

Fig. 3. Posterior abdominal vertebrae of Gymnotocinclus anosteos lacking bifid hemal spines. MCP 41726, paratype, male,40.5mm.

Fig. 4. Scanning electron microscope image of dermal plates at posterior end of caudal peduncle. Gymnotocinclus anosteos, paratype, MCP 41726, male, 40.5 mm SL. LLP = lateral line plates, VPS = ventral plate series, DPS = dorsal plate series.Arrow indicates the modified odontode tips of the last plates on caudal peduncle.

Fig. 5. Left side of neurocranium in ventral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 6. Pectoral girdle in ventral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.