Denticetopsis macilenta (Eigenmann, 1912)

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 : 210-213

Denticetopsis macilenta (Eigenmann, 1912) Figs. 46 , 48-49 , Tables 16-22

Hemicetopsis macilentus Eigenmann, 1912a: 211 , pl. 23, fig. 1 [type locality: British Guiana (= Guyana), Creek below Potaro Landing].– Henn, 1928: 81 [holotype depository].– Ibarra & Stewart, 1997: 44 [holotype depository].– Burgess, 1989: 291 [literature compilation, not habitat data taken from Fernández-Yépez, 1972a].–[not Fernández- Yépez, 1972a: 19, fig. on page 20; not Lasso, 1992: 19].

Pseudocetopsis macilentus .– Schultz, 1944: 252 [in key to species of Pseudocetopsis ].–Evers & Seidel, 2002: 741 [listing].–Vari & Ferraris, 2003: 259 [in check list; distribution].

Diagnosis. Denticetopsis macilenta is distinguished from D. royeroi and D. sauli by the combination of the lack of elongate, symphyseal teeth on the dentary, the lateral line extending posteriorly on the body beyond the abdomen at least onto the caudal peduncle, the presence of dentition on the vomer, a dorsal fin with 5 or 6 segmented rays and with a first ray that is spinous basally, a symmetrical, shallowly-forked caudal fin, and the possession of horizontally-elongate, stellate, dark chromatophores when the chromatophores are expanded. Denticetopsis macilenta differs from D. epa in the proportional length of the pelvic fin (reaching just anterior of the anterior margin of the vent versus to the posterior margin of the vent, respectively) and in the relative position of the eye (located at anterior 0.18-0.19 of HL versus 0.25 of HL, respectively). Denticetopsis macilenta differs from D. praecox in the relative position of the eye (located at anterior 0.18- 0.19 of HL versus 0.25-0.26 of HL, respectively), the number of irregular rows of teeth on the median portions of the premaxilla (three versus two, respectively), in the profiles of the postorbital portion of the head from a dorsal view (convex versus approximately straight, respectively), and in the width of the head as a proportion of the length of the head (head width/HL 0.77-0.84 versus 0.71-0.74, respectively). Denticetopsis macilenta differs from D. iwokrama in the number of caudal (28 to 30 versus 32), preanal (14 to 16 versus 17), and total vertebrae (40 or 41 versus 43), the position of the middle of the orbit (located at anterior 0.18-0.19 of HL versus 0.25 of SL, respectively), and in the width of the head as a proportion of the length of the head (head width/HL 0.77-0.84 versus 0.72, respectively). Denticetopsis macilenta differs from D. seducta in the position of the middle of the orbit (at anterior 0.18-0.19 of HL versus 0.25-0.27 of HL, respectively) and in width of the head as a proportion of the length of the head (head width/HL 0.77-0.84 of HL versus 0.61-0.70 of HL, respectively).

Description. Body moderately stout, very slightly compressed laterally anteriorly and becoming progressively distinctlycompressed posteriorly. Body depth at dorsal-fin origin approximately 0.26-0.27 of SL, and slightly less than HL. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to onto caudal peduncle but falling 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, but posterodorsally-slanted, along base of anal fin. Caudalpeduncle depth approximately 1.5 times caudal-peduncle length.

Head in profile distinctly rounded overall with distinctlyrounded snout. Dorsal profile of head distinctly convex from tip of snout to nape. Ventral profile of head distinctly convex. Margin of snout in dorsal view rounded. Postorbital margins of head convex from dorsal view. Enlarged jaw musculature 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 of snout to posterior margin of orbit and extending dorsal of pectoral-fin insertion by distance equal to width 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 0.18-0.19 of HL. Eye diameter approximately two-thirds of snout length. Interorbital width 1.5 times distance from tip of snout to posterior margin of orbit. 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. Distance between anterior nares approximately equal to distance from tip of snout to posterior margin of orbit. Posterior narial opening located on dorsal surface of head, situated dorsal to anterior half of orbit; narial opening nearly round and completely surrounded by flap of skin of nearly uniform height and with posterior margins of flap in contact.

Mouth inferior; its width approximately two-thirds 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, uniformly-sized, sharply-pointed, and arranged in three, irregular rows medially that taper to two rows laterally. Vomerine teeth arranged in single, arched row with small gap in tooth series at midline. Vomerine teeth stout, conical, and become progressively larger laterally, but with even smallest teeth in series much 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 abruptly taper to one tooth row laterally.

Maxillary barbel slender, its length distinctly longer than distance from tip of snout to rear of eye, and approximately 0.40 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 barbels falling short of posterior margin of opercle.

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.33-0.34 of HL. Length of longest branched dorsal-fin ray equal to approximately one-half of HL. Dorsal-fin spinelet absent. First dorsal-fin ray spinous for basal one-half of length but flexible more distally and without distal filament present in some other species of Cetopsinae . Distal margin of dorsal fin convex, with second branched ray longest. Dorsal-fin origin located at approximately anterior 0.37 of SL and along vertical extending through middle of adpressed pectoral fin. Tip of adpressed dorsal fin falling short of vertical through vent. Posterior most dorsal-fin ray without posterior, membranous attachment to caudal peduncle.

Caudal fin shallowly-forked, symmetrical; tips of lobes bluntly pointed. 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 and approximately at middle of TL. Anal-fin margin slightly convex in all examined specimens. Membranous attachment present between posterior margin of basal two-thirds of posterior most anal-fin ray and body.

Pelvic fin moderate; distal margin slightly convex with middle fin rays longest. Pelvic-fin insertion located anterior to middle of SL and posterior of vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin extending past middle of SL, but falling just short of anterior 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 slightly convex, with middle ray longest. First pectoral-fin ray spinous with smooth margins; ray proportionally short with length approximately one-half of first branched ray.

Coloration in alcohol. Examined specimens largely depigmented. Eigenmann (1912a: 211) reported that Denticetopsis macilenta (the Hemicetopsis macilenta of that author) has “upper surface of head grey; sides with numerous chromatophores, whose rays branch forward and backward from center of cell, giving a strigose effect and looking like little bundles of sticks tied in the middle.” This description is presumably a reference to the horizontally-elongate, expanded, dark chromatophores that are present in most other species of Denticetopsis . The drawing of the holotype in Eigenmann (1912a, pl. 23, fig. 1) showed overall coloration of head and body darker dorsally with abdomen head pale. Dorsal portion of head illustrated as dark as far as ventrally as horizontal extending through pectoral-fin insertion, and pale ventrally except in region of lower lip.

Dorsal fin dark for basal one-half; remainder of fin pale. Anal fin dusky basally, becoming paler distally. Caudal fin with scattered, dark, stellate, chromatophores. Chromatophores less concentrated distally. Pelvic fin pale. Pectoral fin apparently pale.

All barbels apparently pale.

Sexual dimorphism. Examined specimens of Denticetopsis macilenta lack the sexual dimorphism of the dorsal, pectoral, and anal fins that is characteristic of many species within the Cetopsinae , albeit not the other species of Denticetopsis .

Distribution. Denticetopsis macilenta is only known from a limited area in the Potaro River basin of northern Guyana ( Fig. 46 ).

Remarks. Fernández-Yépez (1972a: 19) reported on specimens from the río Aguaro in the state of Guarico, Venezuela, that he identified as Hemicetopsis macilentus . The results of this study indicate, however, that Denticetopsis macilenta is apparently endemic to the Essequibo River basin, Guyana, a considerable distance to the east of the río Aguaro and in a completely different major drainage basin. Furthermore, the specimen illustrated by Fernández-Yépez (1972a: 20) differs in appearance from both the type and non-type specimen of Denticetopsis macilenta examined during this study (compare unnambered figure published in Fernández-Yépez (1972a) with Fig. 47 herein), and most likely represents an unnamed form. We have been unable to locate the specimens cited by Fernández-Yépez and they, furthermore, were not reported on by Milani de Arnal (1991) in her study of the species of the Cetopsinae of Venezuela. Thus, those specimens are likely no longer extant.

Lasso (1992: 19) reported Hemicetopsis macilentus from the lower portions of the río Suapare in the central portions of Venezuela. We have not examined the specimens that served as the basis for this record, but given the restricted known distribution of Denticetopsis macilenta , it is likely that Lasso’s citation of that species from central Venezuela is based on another, perhaps undescribed, species. It is likely that the same situation applies to the report by Machado-Allison et al. (1993: 65) of Hemicetopsis macilentus from localities in the state of Guarico, Venezuela.

Material examined. 9 specimens (29-68 mm SL). Guyana. Kartabo (6°23’N, 58°41’W), AMNH 27692, 1 (68); AMNH 55332, 4 (35- 47); AMNH 55332 SW, 2 (approximately 29-32; specimens cleared and stained). Creek below Potaro Landing (5°23’N, 59°08’W), FMNH 53260, 1 (44; holotype of Hemicetopsis macilentus ); CAS 64605, 1 (52, paratype of Hemicetopsis macilentus ).

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. 48. Denticetopsis macilenta, holotype of Hemicetopsis macilentus, FMNH 53260, 44 mm SL; Guyana, creek below Potaro Landing (5°23’N, 59°08’W).

Fig. 49. Denticetopsis macilenta, original illustration of holotype of Hemicetopsis macilentus (Eigenmann, 1912b, pl. 23, fig. 1), showing distribution of pigmentation and form of horizontally-elongate, dark chromatophores on body.

Fig. 47. Denticetopsis iwokrama, new species, holotype, ANSP 177215, 43 mm SL; Guyana, Essequibo, Siparuni River at Tumble Down Creek, Essequibo River basin (4°48’39"N, 58°51’11"W).