Denticetopsis royeroi Ferraris, 1996

Vari, Richard P., Ferraris Jr, Carl J. & de Pinna, Mário C. C., 2005, The Neotropical whale catfishes (Siluriformes: Cetopsidae: Cetopsinae), a revisionary study, Neotropical Ichthyology 3 (2), pp. 127-238 : 215-216

Denticetopsis royeroi Ferraris, 1996

Figs. 46 , 51 , Tables 16-22

Denticetopsis royeroi Ferraris, 1996: 167 , figs. 4, 12 [type locality: Venezuela, Estado Amazonas, Caño Chola at crossing of San Carlos de río Negro to Solano Road, 1°58’N, 67°00’W].– Taphorn et al., 1997: 85 [ Venezuela].–Evers & Seidel, 2002: 741 [listing].–Vari & Ferraris, 2003: 258 [in check list, distribution].

Diagnosis. Denticetopsis royeroi is distinguished from all of its congeners with the exception of D. sauli by the combination of the possession of elongate, symphyseal teeth on the dentary, a reduced lateral line not extending posteriorly on the body beyond the abdomen, an edentulous vomer, a dorsal fin with only 4 segmented rays and without a spinous first ray, an obliquely-truncate margin of caudal fin, and the lack of horizontally-elongate, stellate, dark chromatophores when the chromatophores are expanded. Denticetopsis royeroi is distinguished from D. sauli by the relative posterior extent of the margin of the maxilla (extending only slightly beyond the posterior margin of the orbit versus extending at least one eye diameter past the posterior margin of the orbit, respectively), the body depth (23% of SL versus 17.1-19.5% of SL, respectively), and the extent of the membranous connection between the caudal and anal fins (membrane without a distinct notch versus distinctly incised, respectively).

Description. Body moderately deep, slightly transverselycompressed anteriorly, becoming increasingly compressed posteriorly. Body depth at dorsal-fin origin equal to length of postorbital portion of head and approximately 0.20 of SL. Lateral line canal incomplete, restricted to abdomen, and limited to canal segment situated posterior of vertical through the posterior limit of base of dorsal fin. Dorsal profile of body straight and very slightly inclined from nape to dorsal-fin origin; nearly straight from dorsal-fin origin to caudal-fin base. Ventral profile of body convex along abdomen, approximately straight, but very slightly posterodorsally-slanted along base of anal fin. Caudal-peduncle length slightly less than onehalf of caudal-peduncle depth.

Head acutely triangular in lateral view and broadly obtusely-rounded anteriorly. Dorsal profile of head slightly convex from tip of snout to posterior nares and straight from nares to posterior of nape. Ventral profile of head gently convex. Profile of snout in dorsal view broadly rounded. Portion of head posterior of nares with lateral margins aligned nearly in parallel in dorsal view. Dorsal surface of posterior portion of head without enlarged jaw musculature apparent externally in many species of Cetopsinae .

Opercular membrane only slightly attached as far posteriorly as vertical through posterior margin of orbit. Opercular opening very wide; extending dorsal of pectoral-fin insertion by distance approximately equal to eye diameter and extending anterior of pectoral-fin insertion for distance equal to approximately one-half of HL.

Eyes situated on lateral surface of head; located entirely dorsal to horizontal extending through pectoral-fin insertion; eye visible in dorsal view, but not in ventral view, of head. Middle of orbit at slightly less than anterior one-third of HL. Eye diameter nearly one-half of snout length. Interorbital width approximately equal to snout length. Anterior narial opening circular, surrounded by short, anteriorly-directed, tubular rim of skin. Opening of anterior nares located at horizontal extending through tip of snout and slightly dorsal to horizontal extending through maxillary-barbel origin. Distance between anterior nares greater than distance from anterior to posterior nares, and approximately equal to distance from tip of snout to posterior margin of orbit. Posterior narial opening large and located near dorsal profile of head and dorsal to region between anterior margin and middle of eye; opening round, with anterior portions of aperture bordered by flap of skin, flap highest anteriorly. Distance between posterior nares slightly less than distance between anterior nares.

Mouth inferior; its width approximately two-thirds of HL. Margin of lower jaw broadly rounded, its posterior extent reaching beyond vertical through posterior margin of eye by distance equal to one eye diameter. Premaxillary tooth patch elongate, continuous across midline; anterior margin convex, posterior margin concave and running in parallel to anterior margin. Teeth in upper jaw small, conical, and sharply-pointed. Vomerine teeth absent. Oral surface of dentary at symphysis expanded medially and bearing irregular patch of somewhat larger conical teeth.

Maxillary barbel slender, its length slightly greater than one-half of HL; barbel origin located near vertical through anterior margin of orbit. Mental barbels slightly shorter than maxillary barbel. Medial mental-barbel origin located along vertical through middle of orbit. Lateral mental-barbel origin located slightly posterior of vertical through posterior margin of orbit. Tips of adpressed mental barbels falling short of posterior margin of opercle.

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.22-0.26 of HL and equal to distance from tip of snout to middle of orbit. Longest dorsal-fin ray slightly less than one-half of HL. Dorsal-fin spinelet absent. First dorsal-fin ray spinous for basal one-half, segmented but flexible distally and without distal filament. Distal margin of dorsal fin slightly convex. Dorsal-fin origin located at approximately anterior 0.39-0.40 of SL and along vertical through middle of adpressed pectoral fin. Tip of adpressed dorsal fin reaching to vertical through anal-fin origin. Posterior most dorsal-fin ray without posterior, membranous attachment to body.

Caudal fin margin obliquely-truncate with dorsal principal fin rays longest. Length of dorsal most principal caudalfin ray approximately 1.5 times length of ventral most fin ray.

Base of anal fin long, approximately 0.40 of SL. Anal-fin origin located along vertical through middle of SL. Anal-fin margin nearly straight, with rays of approximately equal length. Posterior most anal-fin ray with posterior, membranous attachment to first procurrent caudal-fin ray for entire length of ray.

Pelvic fin moderate with distal margin convex and middle fin rays longest. Pelvic fin located entirely anterior to vertical through middle of SL, with pelvic-fin insertion situated along vertical through posterior portion of base of dorsal fin. Tip of adpressed pelvic fin falling slightly short of anal-fin origin. Medial most pelvic-fin ray with membranous attachment to body for basal one-fourth to one-third of its length.

Pectoral-fin length approximately one-half of HL. Pectoral-fin margin very slightly convex, with middle fin rays longest. First pectoral-fin ray somewhat spinous, but flexible distally and without either serrations or distal filament.

Coloration in alcohol. Overall ground coloration of body creamy white with fine, brown, stellate chromatophores that when fully expanded approximately equal to, or less than, width of eye. Dorsal and lateral surfaces of nape, snout, and head with few scattered, dark chromatophores extending as far ventrally as horizontal running through eye. Portion of cheek ventral of orbit, operculum, and ventral surface of head and abdomen with few widely-scattered, dark chromatophores. Larger chromatophores present on head and lateral surface of body anterior to vertical through vent, with chromatophores located more posteriorly in that region notably smaller. Chromatophores evenly distributed over most of caudal region, but more densely concentrated on, and along side of, dorsal midline. Single row of dark chromatophores situated dorsal to base of anal fin.

Dorsal fin with diffuse, dark spot no larger than eye covering base of first two fin rays. Pectoral, pelvic, and anal fins without dark pigmentation. Caudal fin with small dark chromatophores irregularly arranged along margins of each ray.

Barbels unpigmented or with only one or two, dark spots basally.

Sexual dimorphism. Inasmuch as only one specimen of Denticetopsis royeroi is known, it is impossible to evaluate whether this species demonstrates the sexual dimorphism in the dorsal, pectoral, and anal fins that is present in many species within the Cetopsinae , albeit not in the other species of Denticetopsis .

Distribution. Denticetopsis royeroi is only known from the holotype collected in a tributary to the upper río Negro, Venezuela ( Fig. 46 ).

Material examined. 1 specimen (18.5 mm SL). Venezuela Amazonas: Caño Chola, at crossing of road from San Carlos de río Negro to Solano (1°58’N, 67°00’W), MBUCV V-26785, 1 (18.5, holotype of Denticetopsis royeroi ) .

Figures

Fig. 46. Map of central and northern SouthAmerica showing geographic distribution of Denticetopsis epa (1 = holotype locality), Denticetopsis iwokrama (2 = holotype locality), Denticetopsis macilenta (3 = holotype locality of Hemicetopsis macilenta), Denticetopsis praecox (4 = holotype locality), Denticetopsis royeroi (5 = holotype locality), Denticetopsis sauli (6 = holotype locality), and Denticetopsis seducta (7 = holotype locality) (some symbols represent more that one locality and/or lot of specimens).

Fig. 51. Denticetopsis royeroi, holotype, MBUCV V-26785, 18.5 mm SL; Venezuela,Amazonas, Caño Chola, at crossing of road from San Carlos de río Negro to Solano (1°58’N, 67°00’W) (photo taken shortly after capture).