Denticetopsis seducta, Vari & Ferraris Jr & de Pinna, 2005

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 : 218-222

Denticetopsis seducta , new species

Figs. 46 , 53 , Tables 16-22

Diagnosis. Denticetopsis seducta is distinguished from D. royeroi and D. sauli by the combination of the lack of elongate, symphyseal teeth on the dentary, a reduced lateral line extending posteriorly on the body beyond the abdomen onto at least the caudal peduncle, the presence of dentition on the vomer, a dorsal fin with 5 or 6 segmented rays and with the first ray that is spinous basally, a symmetrical, shallowlyforked caudal fin, and the possession of horizontally-elongate, dark, stellate chromatophores when the chromatophores are expanded. Denticetopsis seducta differs from D. epa in the relative position of the origin of the anal fin (located distinctly anterior of vertical through middle of TL versus approximately at vertical through middle of TL, respectively) and the relative depth of the caudal peduncle versus the length of the caudal peduncle (depth/length 1.33-1.5 versus 1.15-1.3, respectively). Denticetopsis seducta differs from D. macilenta in the position of the middle of the orbit (located at anterior 0.25-0.27 of HL versus 0.18-0.19 of HL, respectively) and in the relative width of the head (head width/HL 0.61-0.70 versus, 0.77-0.84, respectively). Denticetopsis seducta differs from D. praecox in the number of premaxillary tooth rows (three rows of teeth present in all but smallest examined specimens versus two rows of teeth present at all body sizes, respectively), in the pigmentation of the caudal fin (without a distinct, pale region in the distal portions of the middle fin rays versus the presence of a distinct, pale region in the distal portions of the middle fin rays, respectively), and in the degree of pigmentation of the pectoral fin (heavily pigmented versus lightly pigmented, respectively). Denticetopsis seducta differs from D. iwokrama in the number of caudal (26 to 31 versus 32, respectively), preanal (14 to 17 with 17 in only 1 of 23 specimens examined for this feature versus 17, respectively), and total vertebrae (39 to 42 with a mode of 40 and 42 in only 1 of 31 specimens examined for this feature versus 43, respectively) and in the pigmentation of the pectoral fin (heavily pigmented versus lightly pigmented, respectively).

Description. Body ranges from elongate to moderately deep depending on overall condition of individual; slightly-compressed laterally anteriorly and becoming progressively distinctly-compressed posteriorly. Body depth at dorsal-fin origin approximately 0.20-0.30 of SL depending on overall condition of specimen. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to onto caudal peduncle but falling to varying degrees short of posterior margin of hypural plate. Dorsal profile of body straight from nape to dorsal-fin origin and straight from dorsal-fin origin to caudal-fin base. Ventral profile of body convex along abdomen, approximately straight to slightly convex, but posterodorsally-slanted, along base of anal fin. Caudal-peduncle depth approximately one and one-third times caudal-peduncle length.

Head in profile acutely triangular overall with bluntlypointed snout. Dorsal profile of head slightly convex from tip of snout to nape. Ventral profile of head slightly convex. Margin of snout in dorsal view rounded. Postorbital margins of head running nearly in parallel from dorsal view. Enlarged jaw musculature very evident externally on dorsal surface of postorbital portion of head.

Opercular membrane attaching to isthmus only anterior of vertical through pectoral-fin insertion. Opercular opening moderate; extending ventral of pectoral-fin insertion by distance equal to distance from tip snout to posterior margin of orbit and extending dorsal of pectoral-fin insertion by distance equal to diameter of eye.

Eye 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 approximately anterior one-fourth of HL. Eye diameter approximately one-half of snout length. Interorbital width slightly greater than distance from tip of snout to middle of eye. Anterior narial opening circular, surrounded by short, anteriorly-directed, tubular rim of skin. Opening of anterior nares located along horizontal extending through maxillary-barbel origin and ventral of horizontal extending through tip of snout. Distance between anterior nares approximately equal to distance from tip of snout to middle of eye. Posterior narial opening located on dorsal surface of head, situated along vertical through anterior margin of orbit; narial opening nearly round and completely surrounded by flap of skin of nearly uniform height with posterior margins of flap in contact.

Mouth inferior; its width approximately one-half of HL. Margin of lower jaw gently rounded, its posterior limit reaching to vertical through posterior margin of orbit. Premaxillary tooth patch in form of gently-arched band continuous across midline and with anterior margin convex and posterior margin concave and running in parallel to anterior margin. Teeth on premaxilla small, conical, sharply-pointed, and arranged in two, regular rows of uniform-sized teeth across premaxilla, with variable number of teeth anterior of those two series; anterior teeth irregular in smaller individuals and forming third irregular row in larger specimens. Vomerine teeth arranged in single, arched row with small gap in tooth series at midline. Vomerine teeth stout, conical, and become progressively larger laterally, with even smallest teeth in series larger than teeth on premaxilla. Dentary teeth comparable in shape to, but larger in size than, premaxillary teeth. Dentary dentition consisting of three or four irregular rows medially that taper to one row laterally.

Maxillary barbel slender, its length approximately equal to distance from tip of snout to rear of eye, and approximately one-third to one-half of HL; barbel origin located ventral to middle of orbit. Medial mental barbel slightly shorter than lateral mental barbel, with latter approximately equal in length to maxillary barbel. Medial mental-barbel origin located along vertical through rictus. Lateral mental-barbel origin situated slightly posterior of vertical through medial mental-barbel origin. Tips of adpressed mental barbel falling short of posterior margin of opercle.

Dorsal fin moderately large overall with length of its base approximately 0.29-0.32 of HL. Length of longest branched dorsal-fin ray equal to approximately one-half of HL. Dorsalfin spinelet absent. First dorsal-fin ray spinous for basal onehalf of length but flexible more distally, and without distal filament present in some species within Cetopsinae . Distal margin of dorsal fin convex, with second branched ray longest. Dorsal-fin origin located at anterior 0.33-0.35 of SL and along vertical extending through middle of adpressed pectoral fin. Tip of adpressed dorsal fin reaching vertical through vent. Posterior most dorsal-fin ray without posterior, membranous attachment to caudal peduncle.

Caudal fin shallowly-forked, symmetrical; tips of lobes rounded. Length of longest caudal-fin ray approximately 1.5 times length of middle fin rays.

Base of anal fin moderately long. Anal-fin origin located distinctly posterior of middle of SL but falling distinctly short of middle of TL. Anal-fin margin slightly convex in all examined specimens. Membranous attachment present between posterior margin of basal one-half of posterior most anal-fin ray and caudal peduncle.

Pelvic fin moderate; distal margin slightly convex with middle fin rays longest. Pelvic-fin insertion located anterior to middle of SL and along vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin extending past middle of SL to at least anterior, but not posterior, margin of vent. Medial most pelvic-fin ray with membranous attachment to body along basal one-fourth of its length.

Pectoral-fin length approximately one-half of HL. Pectoral-fin margin distinctly convex with middle ray longest. First pectoral-fin ray spinous with smooth margins, spinous portion of ray proportionally short with length approximately one-half that of first branched fin ray.

Coloration in alcohol. Overall coloration of head and body medium-brown to nearly black and somewhat, to distinctly, darker dorsally. Abdomen pale. Dark coloration primarily formed of large, stellate, horizontally-elongate, dark chromatophores when chromatophores expanded. Body also with few, scattered, discrete, dark spots. Head dark dorsally, with dark pigmentation continuing ventrally as far as horizontal extending through pectoral-fin insertion.Amount of pigmentation in transition zone between dark and light areas on side of head highly variable. Head pale ventrally with little or no pigmentation around lower lip.

Dorsal fin dark for basal one-half except for pale anterior and posterior most rays; distal one-half of remainder of fin pale overall but with scattered, dusky pigmentation. Anal fin dusky basally, becoming progressively paler distally. Caudal fin dusky with pigmentation somewhat more pronounced basally in some individuals but uniformly dusky in other specimens. Pelvic fin pale. Pectoral fin ranging from dusky to dark within available population samples.

Maxillary barbel with dusky, basal pigmentation and pale distally. Mental barbels pale.

Sexual dimorphism. The examined specimens of Denticetopsis seducta do not demonstrate the sexual dimorphism of the anal, dorsal, and pectoral fins that is present in many species of the Cetopsinae , albeit not in the other species of Denticetopsis .

Distribution. Denticetopsis seducta has a relatively wide, albeit scattered, distribution in the central and western portions of the Amazon basin and possibly the southwestern portions of the río Orinoco basin ( Fig. 46 ; see also “Remarks” below).

Etymology. The species name, seducta , from the Latin for remote or apart, is in reference to the disjunct distribution of this species relative to the other members of Denticetopsis .

Remarks. The type series of Denticetopsis seducta that originated in the río Ucayali basin and in the region of Iquitos in northeastern Peru, and the non-type population samples of the species from the rio Aripuanã in the rio Madeira basin, Brazil agree in all examined features. A single specimen that originated in the upper río Napo in eastern Ecuador (ANSP 139105) and which is tentatively identified as Denticetopsis seducta has slightly higher number of total vertebrae (43) than the 39 to 42 total vertebrae that occur in the other examined specimens assigned herein to that species (datum of that specimen not included in Tables 16 to 22). Additional population samples of Denticetopsis from the upper río Napo basin are necessary to determine whether this specimen represents yet another undescribed species.

A single specimen from the southwestern portions of the río Orinoco basin in Colombia (ANSP 139573) which would

Branched Anal-fin Rays

19202122232425 D. epa 3 5 4 2

D. iwokrama 1

D. macilenta 1 - 2 2

D. praecox 4 5 - - 1 D. royeroi - - - - - - - D. sauli - - - - - - - D. seducta 1 1 1 4 1

represent the only record of the species from outside the Amazon basin, may also be D. seducta . A definitive identification of that population must, however, await the availability of larger population samples of that form from that portion of the río Orinoco system.

Given the uncertainty as the identification of the single specimens from both the upper río Napo and the western río Orinoco basin, those localities are not plotted on Fig. 46 .

Material examined. 39 specimens (39, 20-51 mm SL). Holotype. Peru. Loreto: Caño “Sabalito,” small creek on terra firma approximately 25 mi (=km) S of Iquitos (4°14’45"S, 73°24’57"W), M. H. Sabaj et al., 11 August 2001, ANSP 178466 , 1 (39) . Paratypes. 11 specimens (11, 20-51 mm SL). Peru. Loreto: Caño “Sabalito,” small creek on terra firma approximately 25 mi (= 40 km) S of Iquitos (4°14’45"S, 73°24’57"W), collected with holotype, ANSP 179141 , 2 (20-46) ; MUSM 20297 , 2 (26-32) ; USNM 372758 , 1 , (36) . Río Ucayali drainage, Quebrada Copal, at km 15 on road from Jenaro Herrera to Colonia Angamos, S. Kullander et al., 29 August 1983, NRM 18387, 3 (33-40) . Ecuador. Sucumbios: tributary to río Cuyabeno, about 10 km N of Marian and 1 km S of río Cuyabeno (0°1’59"S, 76°20’0"W), D. J. Stewart et al., 30 Nov 1983, FMNH 111689 , 3 (30-51) . Non-type specimens. 30 specimens (26-39 mm SL). Brazil. Amazonas: Igarapé Açu, 7 km below Santo Antonio do Iça, left bank of rio Solimões (3°05’S, 67°57’W), MZUSP 23545 , 1 (39) . Mato Grosso: Igarapé Ingazeiro, 20 km above mouth of rio Canumã of rio Aripuanã , below Dardanelos, MZUSP 37813 , 27 (26-31.5; 5 specimens, 27-38 mm, cleared and stained).

222 The Neotropical whale catfishes

The following specimens may also be Denticetopsis seducta (see “ Remarks ” above): Colombia. Meta: Caño Emma, Finca El Viento 33.5 km NE of Puerto Lopez ( río Orinoco basin; approximately 4 o 08’N, 72 o 39’W), ANSP 139573 , 1 (31.0) . Ecuador. Napo: Small stream approximately 1 mile (=1.6 km) up río Payamino from its mouth at Puerto Coca (=Puerto Francisco de Orellana), ANSP 139105 , 1 (30).

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. 53. Denticetopsis seducta, new species, holotype,ANSP 178466, 39 mm SL; Peru, Loreto, Caño “Sabolito,” small creek on terra firma approximately 25 mi (= 40 km) south of Iquitos (4°14’45"S, 73°24’57"W).