Rhyacoglanis, Shibatta & Vari, 2017

Shibatta, Oscar Akio & Vari, Richard P., 2017, A new genus of Neotropical rheophilic catfishes, with four new species (Teleostei: Siluriformes: Pseudopimelodidae), Neotropical Ichthyology 15 (2), No. e 160132, pp. 1-30 : 4-5

Rhyacoglanis , new genus

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Type-species. Pimelodus (Pseudopimelodus) pulcher Boulenger, 1887 .

Diagnosis. Rhyacoglanis is distinguished in the Pseudopimelodidae by three characters, the first two of which autapomorphic: 1) the dorsal and lateral surfaces of the head are grey with a light blotch on the cheek (vs. completely grey in Cruciglanis and Pseudopimelodus , black in Batrochoglanis and Microglanis and ligth in Cephalosilurus and Lophiosilurus ); 2) the dark stripe along the midline of the upper and lower caudal-fin lobes is confluent with a dark caudal peduncle blotch (vs. dark stripes on caudal fin not confluent with dark caudal-peduncle pigmentation or absent altogether); 3) 30-35 total vertebrae (vs. 36-44). Rhyacoglanis differs from other pseudopimelodids except Cruciglanis and Pseudopimelodus by the combination of the presence of the vomer, the anterior nostril located slightly posterior of the rictus nearly at the vertical through the posterior of the base of the maxillary barbel, and the thick skin on the pectoral-fin spine. Rhyacoglanis differs from Cruciglanis and Pseudopimelodus in the number of total vertebrae (31- 35 vs. 41-44 in Cruciglanis ; 41-42 in Pseudopimelodus ). It differs from Pseudopimelodus in the long posterior cleithral process almost reaching the vertical through the dorsal-fin origin (vs. very short process falling short of that vertical). Rhyacoglanis is distinguished from Cruciglanis by the lack of lateral processes on the second basibranchial (vs. presence of these processes resulting in a cross-shaped ossification) and a pelvic-fin origin at the vertical through the terminus of the dorsal-fin base (vs. slightly posterior of that point). Additional diagnostic characters for Rhyacoglanis in the Pseudopimelodidae are the small maximum body size (less than 100 mm SL vs. more than 100 mm SL in Cephalosilurus , Lophiosilurus and Pseudopimelodus ); the rounded anterior head outline in dorsal view (vs. an almost trapezoidal head in Lophiosilurus ); the terminal mouth opening forward (vs. superior mouth in Lophiosilurus or supraterminal in Cephalosilurus , and Pseudopimelodus ); the very wide frontal fontanel (vs. a narrow fontanel in Cruciglanis and Pseudopimelodus ); the thin, elongate, arched mesocoracoid in ventral view (vs. triangular in Pseudopimelodus ); a posterolaterally projected dentigerous premaxillary plate (vs. projection absent in Microglanis ); the laterally expanded anterior transverse process of the fourth vertebrae (vs. unexpanded process in Batrochoglanis , Cephalosilurus , Lophiosilurus and Microglanis ); the forked caudal fin with pointed or rounded lobes and a lower lobe usually longer than the upper lobe (vs. an emarginate caudal with the upper lobe longer than the lower lobe in Batrochoglanis and Microglanis , or a round caudal-fin margin in Cephalosilurus and Lophiosilurus ); the elongate caudal peduncle (vs. a short peduncle in Batrochoglanis ); the adult pigmentation pattern of two or three well-defined dark body bands (vs. bands absent at least at some point in ontogeny in Cephalosilurus and Lophiosilurus ); and the head pigmentation slightly darker than the ground body coloration (vs. the similar head and body pigmentation in Cephalosilurus and Lophiosilurus ).

Etymology. Rhyacoglanis , from the Greek rhyax = torrent + glanis = catfish; indicating a catfish inhabiting running waters in reference to the habitat of the genus. Gender masculine.

Key to species of Rhyacoglanis

1a. Body with three dark bands - subdorsal, subadipose and caudal peduncle; sometimes inconspicuous or absent..... 2

1b. Body with two dark bands - an anteroposteriorly expansive band formed from a fusion of the subdorsal and subadipose bands, and a separate caudal-peduncle band ............................. R. seminiger (rio Juruena basin)

2a. Dorsal regions of subdorsal and subadipose bands separate.......................................................................... 3

2b. Dorsal regions of subdorsal and subadipose bands united by dark stripe along dorsal portion of body...... R. pulcher (western Amazon basin)

3a. Dark caudal-peduncle band uniformly pigmented .......... 4

3b. Dark caudal-peduncle band with unpigmented central section ............................. R. annulatus (río Orinoco basin)

4a. Caudal-fin lobes rounded; body covered with multiple small dark spots; dark bands on body inconspicuous to absent ............................. R. epiblepsis (rio Madeira basin)

4b. Caudal-fin lobes pointed; body with few small dark spots; dark bands on body conspicuous .......................... ............................ R. paranensis (upper rio Paraná basin)