Rhyacoglanis annulatus, 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 : 5-8

Rhyacoglanis annulatus , new species

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Fig. 2; Tab. 1

Holotype. ANSP 160625 , 42.5 mm SL, Venezuela, Amazonas, río Orinoco, Raudales de Atures, at Culebra , approximately 7 km S of Puerto Ayacucho, ca. 05 o 35’N 67 o 31’W, 11 Nov 1985, W. G. Saul, R. Royero, O. Brull, L. Aguana & R. Peck.

Paratype. Venezuela. Amazonas. ANSP192597 , 1 , 27.0 mm SL, río Orinoco basin, río Ventuari, exposed cobble beach along base of Cerro Moriche , about 1 km upstream of Moriche community, 167 km E-NE of San Fernando de Atabapo , 04 o 45’12.46”N 66 o 22’21”W, 3 Apr 2010, M. H. Sabaj Pérez, N. K. Lujan, D. C. Werneke , T. P. Carvalho, S . V. Meza V. & O. León Mata .

Diagnosis. Rhyacoglanis annulatus is diagnosed from congeners by the caudal-peduncle band with an unpigmented central region (vs. band uniformly dark). Rhyacoglanis annulatus differs from R. paranensis in the distance between the anus and anal-fin origin (15.8-16.2 vs. 6.5-12.7% SL), the distance between the pelvic-fin origin and anus (8.2-9.6% vs. 9.9-17.3% SL) and total vertebrae (31-33 vs. 34-35). Rhyacoglanis annulatus is distinguished from R. epiblepsis by distally pointed caudal-fin lobes (vs. rounded), in the distance between the anus and anal-fin origin (15.8-16.2 vs. 11.5-15.0% SL), the distance between the pelvic-fin origin and anus (8.2- 9.6 vs. 10.0-14.3% SL), pectoral-fin spine length (8.1- 20.0 vs. 12.6-16.7% SL), dorsal-fin spine length (16.6- 16.7 vs. 9.8-15.3% SL), the number of total vertebrae (34- 35 vs. 31-33), and possession of few dark body spots (vs. numerous less intense spots). Rhyacoglanis annulatus is separable from R. seminiger by the separate subdorsal and subadipose bands (vs. bands fused), the distance between the anus and anal-fin origin (15.8-16.2 vs. 6.8-11.6% SL), the distance between the pelvic-fin origin and anus (8.2- 9.6 vs. 12.4-15.0% SL) and total vertebrae (34-35 vs. 31- 33). Rhyacoglanis annulatus is separated from R. pulcher in the distance between the anus and anal-fin origin (15.8- 16.2 vs. 13.8-15.2% SL) and the distance between the pelvic-fin origin and anus (8.2-9.6 vs. 11.1-14.0% SL).

Description. Body proportions presented in Tab. 1. Body depressed from snout tip to dorsal-fin origin; progressively posteriorly compressed from that point to caudal-fin base. Dorsal profile of posterodorsal portion of head and body nearly straight to dorsal-fin origin; dorsal-fin base inclined slightly posteroventrally and nearly straight; region between posterior terminus of dorsal-fin base and adipose-fin origin nearly straight. Ventral profile of head and body nearly straight from lower jaw margin to posterior of anal-fin base. Caudal peduncle profile slightly concave along dorsal and ventral margins.

Head depressed; slightly longer than wide. Anterior margin convex in dorsal view. Head with well developed unculiferous tubercles primarily dorsally. Mouth terminal and wide; width more than one-half of HL. Upper jaw slightly longer than lower jaw. Lips thick; most developed on lateral surface of lower jaw and proximate to rictus. Premaxillary tooth plate posterolaterally pointed. Anterior nostril located immediately posterior to vertical through rictus. Eye small, superior, covered by skin, slightly posterior of anterior one-third of HL. Opercular membrane well developed; margin reaching pectoral-fin origin. Maxillary barbel base enlarged. Tip of adpressed barbel reaching pectoral-fin origin. Tip of adpressed inner mental barbel extending slightly beyond base of outer mental barbel, but falling short of barbel tip. Tip of adpressed outer mental barbel reaching pectoralfin origin.

Dorsal fin trapezoidal overall; distal margin rounded; length of longest ray equal to fin-base length. Dorsal-fin origin immediately posterior to anterior one-third of body and anterior to one-half of SL. Tip of adpressed dorsal fin reaching midpoint between dorsal and adipose-fin bases. First dorsal-fin ray (spinelet) small, rigid, and forming dorsal-fin spine-locking mechanism. Second ray a spine with anterior margin smooth and posterior margin with retrorse serrations. Dorsal-fin rays I,6*(2). Adipose fin long; its base longer than that of dorsal fin; posterior margin free and slightly angular. Pectoral fin slightly triangular overall with posterior margin rounded. Tip of adpressed pectoral fin reaching vertical through middle of dorsal-fin base. First pectoral-fin ray strong, rigid and developed as spine with similar size serrae along anterior and posterior margins. Serrations on posterior margin retrorse. Tip of bony pectoralfin spine notched ( Fig. 3a). Pectoral-fin rays I,6* rays (2). Pelvic fin almost triangular with posterior margin rounded. Pelvic-fin origin at vertical through base of penultimate dorsal-fin ray. Tip of adpressed pelvic fin falling short of anal fin but extending beyond vertical through adiposefin origin. Pelvic-fin rays i,5*(2). Anal fin margin rounded distally; base shorter than that of adipose-fin. Anal-fin rays iii,7*(2). Caudal fin forked with pointed lobes; ventral lobe slightly longer than dorsal lobe. Principal caudal-fin rays i,6,8,i*(2). Dorsal procurrent rays 12(1) or 14*(1); ventral procurrent rays 9(1) or 10*(1).

Posterior cleithral process well developed, pointed, reaching vertical through dorsal-fin origin. Axillary pore present. Lateral line complete. Total vertebrae 34(1) or 35*(1). Ribs 9*(2). Gill rakers 1,1,4*(1) or 1,1,5(1).

Color in alcohol. Ground color light brown. Head with dark spots dorsally, on operculum, and ventral to orbit. Region over adductor mandibulae muscle lightly colored. Two small dark spots posterodorsally on head. Subdorsal band narrow, somewhat triangular. Subadipose band nearly rectangular. Region between bands with scattered small, irregularly shaped, dark spots. Caudal-peduncle band irregularly shaped; central region unpigmented. Dorsal fin dark on basal two-thirds and unpigmented posteriorly and distally. Adipose fin with dark pigmentation anteriorly, anterobasally and centrally. Caudal fin hyaline overall with thin arched dark band transversing each lobe; overall pattern resembling sideways V; distal region lightly colored. Anal fin hyaline other than dark blotch near base and series of dark spots aligned across middle of rays. Pectoral and pelvic fins hyaline overall; each crossed by dark stripe.

Geographical distribution. Rhyacoglanis annulatus is known solely from the southern portions of the río Orinoco basin in Venezuela ( Fig. 4).

Etymology. The specific name, annulatus , is a Latin adjective meaning ringed, in reference to the caudalpeduncle band with a light inner region.

Conservation status. Only two specimens of R. annulatus are known, representing two localities. This rarity in collections suggests that the species may be rare in nature as well. The geographic distribution of R. annulatus in the upper río Orinoco basin must be wide, as the localities cover a broad geographic region with up to 40,000 km 2. However, in light of extent of occurrence superior to 20,000 km 2, and lack of evidence indicating population decline or fluctuations, R. annulatus should be assigned a Least Concern (LC) IUCN (2016) status.

Remarks. Rhyacoglanis annulatus is known from two preserved specimens collected in widely separated areas. An internet site (Fluvial, by Oliver Lucanus) (http://www.fluvalaquatics.com/ca/explore/expeditions/ metaexpedition/#.VP3nn_nF-FU), shows a third specimen identified as Pseudopimelodus cf. raninus which is rather R. annulatus as evidenced by the unique caudal-peduncle pigmentation. This specimen from the río Meta represents a distinctly more northwesterly record for the species in the río Orinoco system.