Cetopsidium pemon, 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 : 144-147

Cetopsidium pemon , new species

Figs. 2 , 8-9 , Tables 2-8

Hemicetopsis minutus .–Taphorn & García Tenía, 1991: 35 [ Venezuela, Bolivar, lower río Caroni; possibly in part, see “Remarks”].

Diagnosis. Cetopsidium pemon differs from C. ferreirai in the degree of development of the first rays of the dorsal and pectoral fins (with distal filaments present in presumed mature males as indicated by the possession of a distinctly convex anal-fin margin versus absent in such specimens, respectively), the overall form of the head (profile of head distinctly pointed versus anteriorly rounded in lateral view, respectively), and in the length of the snout (approximately 3 times diameter of eye versus approximately 2 times diameter of eye, respectively). Cetopsidium pemon differs from C. minutum in the length of the pelvic fin (barely reaching, or falling short of, the vent versus reaching to the anal-fin origin, respectively). Cetopsidium pemon differs from C. morenoi in the form of the dark pigmentation on the body (small, point-like, scattered chromatophores located on the dorsal and lateral surfaces of the head versus large, stellate chromatophores present in those areas, respectively) and in the degree of development of the adductor mandibular muscles (moderately-developed and not particularly obvious externally versus very well developed and distinctly obvious externally on dorsolateral portion of head, respectively). Cetopsidium pemon differs from C. orientale in the overall coloration (small, point-like, scattered chromatophores over the dorsal and lateral surfaces of the head and body versus large, stellate, dark chromatophores densely covering the dorsal and lateral surfaces of the head and body, respectively), and in the alignment of the dorsal and ventral profiles of the portion of the body posterior of the base of dorsal fin (converging posteriorly versus running in parallel, respectively). Cetopsidium pemon differs from C. roae in the position of the vent (located proximate to versus distinctly separated from the base of the anterior most anal-fin ray, respectively), in the alignment of the dorsal and ventral profiles of the portion of the body posterior of the base of dorsal fin (converging posteriorly versus running in parallel, respectively), and in the degree of development of the first rays of the dorsal and pectoral fins (with distal filaments present in presumed mature males as indicated by the possession of a distinctly convex anal-fin margin versus the apparent absent of these structures, respectively).

Description. Body moderately robust, somewhat compressed laterally anteriorly and becoming progressively more compressed posteriorly. Body depth at dorsal-fin origin approximately 0.22-0.24 of SL, and slightly less than HL. Lateral line on body incomplete, unbranched, and midlateral; extending from vertical through pectoral-fin base posteriorly to region dorsal of base of anal fin, but falling short of caudal peduncle. 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 slightly convex along abdomen, approximately straight, and slightly posterodorsally-inclined along base of anal fin. Caudal-peduncle depth approximately equal to, or slightly greater than, caudal-peduncle length.

Head in profile acutely triangular overall with bluntlypointed snout. Dorsal profile of head slightly convex from tip of snout to vertical through posterior margin of orbit and broadly convex from that point to nape. Ventral profile of head slightly convex. Margin of snout in dorsal view broadly rounded. Postorbital margins of head slightly convex on each side from dorsal view. Enlarged jaw musculature very evident externally on dorsal and lateral surfaces of postorbital portion of head.

Opercular membrane attaching to isthmus only in area anterior of vertical through pectoral-fin insertion. Opercular opening moderately-elongate; extending anteroventral of pectoral-fin insertion by distance approximately equal to onehalf of HL 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 located at approximately anterior one-fourth of HL. Eye diameter approximately one-half of snout length. Interorbital width approximately equal to distance from tip of snout to middle of orbit. Anterior narial opening circular, surrounded by short, anteriorly-directed, tubular rim of skin. Opening of anterior nares located slightly dorsal of horizontal extending through maxillary-barbel origin and at, or slightly ventral of, horizontal running through tip of snout. 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 one-third of orbit; narial opening nearly round and with flap of skin extending along anterior two-thirds of rim of aperture and flap highest anterolaterally.

Mouth subterminal; its width approximately 0.48-0.52 of HL. Margin of lower jaw gently rounded, its posterior limit reaching to vertical through middle of orbit. Premaxillary tooth patch in form of gently-arched band, continuous across midline 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 three more or less regular rows of uniform-sized teeth across entire premaxilla. Vomerine teeth arranged in single, arched row with distinct gap in series at midline. Vomerine teeth stout, conical, and of approximately uniform size, but not substantially larger than teeth on premaxilla. Dentary teeth comparable in shape and size to premaxillary teeth. Dentary dentition consisting of three irregular rows medially that taper to one row laterally.

Maxillary barbel slender, its length approximately equal to distance from anterior margin of orbit to posterior margin of opercle, and slightly greater than three-fourths of HL; barbel origin located ventral to anterior margin of orbit. Medial mental barbel slightly shorter than lateral mental barbel, with latter shorter than 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 extending to, or slightly past, posterior margin of opercle.

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.36-0.41 of HL. Longest branched dorsal-fin ray, excluding distal filament on first ray present in mature males, equal in length to approximately two-thirds of HL. Dorsal-fin spinelet present, first dorsal-fin ray spinous for basal one-half of length, flexible more distally, and prolonged as distal filament in at least some mature males. Distal margin of dorsal fin slightly convex, with first branched ray longest. Dorsal-fin origin located at approximately anterior 0.33 of SL and along vertical extending through middle of adpressed pectoral fin. Tip of adpressed dorsal fin, excluding distal filament of first ray present in mature males, reaching, or falling slightly short of, vertical through vent. Posterior most dorsal-fin ray with slight, basal, posterior, membranous attachment to body.

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

Base of anal fin moderately long. Anal-fin origin located distinctly posterior of middle of SL and anterior of middle of TL. Anal-fin margin nearly straight in most examined specimens, but convex in presumed mature males as evidenced by possession of distal filaments on first rays of dorsal and pectoral fins. Posterior most anal-fin ray with slight, membranous attachment to body.

Pelvic fin small; 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 and barely reaching anterior margin of vent. Medial most pelvic-fin ray with membranous attachment to body along basal one-half of its length.

Pectoral-fin length, excluding distal filament on first ray of mature males, 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 short with length slightly more than one-half that of first branched ray and prolonged as well-developed distal filament in mature males ( Fig. 9 ).

Coloration in alcohol. Overall ground coloration of head and body pale and overlain with rounded, brown chromatophores. Dark pigmentation on head and body tends to be more concentrated dorsally but never forming intensely dark pigmentation. Ventral surface of abdomen and head pale or with few, widely-scattered, brown chromatophores. Lower lip with single row of dark chromatophores paralleling margin of lip.

Dorsal and anal fins pale, with scattered, dark chromatophores basally; pigmentation more developed on anterobasal portion of dorsal fin of some specimens. Caudal fin with widely scattered, tiny, dark chromatophores extending posteriorly to middle of fin in some, but not all, specimens. Pelvic and pectoral fins pale.

All barbels pale.

Sexual dimorphism. Presumed mature males of Cetopsidium pemon ( Figs. 8 , 9 ) have the first ray of the dorsal and pectoral fins extending past the fin margin as a distinct filament contrary to the absence of such a prolongation on these rays in females and immature males. Mature males of the species also have the anal-fin margin broadly convex rather than straight as in females and immature males.

Distribution. Cetopsidium pemon is known from the río Caroni and the río Caura basins, southern tributaries of the río Orinoco in eastern Venezuela, the río Meta basin of the western portions of the río Orinoco system in eastern Colombia, and the upper portions of the rio Branco in northern Brazil ( Fig. 2 ).

Etymology. The species name, pemon , is in reference to the Pemon, an Amerindian tribe whose traditional territories included the area of the type locality.

Remarks. Taphorn & García Tenía (1991: 35) reported Hemicetopsis minutus (the Cetopsidium minutum of this study) from the río Claro system in the río Orinoco basin of Venezuela. Examination of at least some of the specimens that apparently served as the basis for that record demonstrated that they are rather Cetopsidium pemon . Lasso et al. (1990: 117) reported Hemicetopsis minutus (= Cetopsidium minutum herein) from the upper río Caroni in the Gran Sabana region of southeastern Venezuela. All specimens of Cetopsidium minutum examined in this study originated in the Essequibo River system of Guyana and the report of that species in the río Caroni basin by Lasso et al. (1990) may be based on specimens of C. pemon , an externally-similar species whose range includes at least portions of the río Caroni basin. The report of Pseudocetopsis sp. from the lower portions of the río Caura by Machado et al. (2003: 267) is also likely based on material of Cetopsidium pemon on the basis of the known distribution of that species.

One lot of four examined specimens that was collected in Bolivar state of Venezuela in the río Abacapa ( FMNH 45708 ) is tentatively identified as Cetopsidium pemon based on external features. These specimens are, however, in somewhat poor condition; a situation that complicates direct comparisons with apparently conspecific samples. The río Abacapa sample demonstrates some apparent internal differences relative to other population samples of that species; however, an evaluation of the significance of these features must await the osteological examination additional material from the río Abacapa region .

Material examined. 33 specimens (20-42.6 mm SL). Holotype. Venezuela. Bolivar: río Caroni, at mouth of río Claro (7°54’45"N, 63°02’35"W), D.C. Taphorn et al. 15 Mar 1988, MCNG 19475 , 1 , mature male (25). Paratypes. 12 specimens (23-41.5 mm SL). Venezuela. Bolivar: río Caroni at mouth of río Claro (7°54’45"N, 63°02’35"W), MCNG 45650 , 1 (23, formerly MCNG 19475 , in part) ; USNM 375959 , 1 (30, formerly MCNG 19475 , in part) ; collected with holotype. Río Claro, east of Los Tanques (7°55’20"N, 63°06’05"W), D. C. Taphorn et al., 5 Mar 1988, MCNG 18422 , 3 (27.5-41.5) . Río Paragua, opposite mouth of río Carapo , at sand beach, C. J. Ferraris Jr. et al., AMNH 91188 , 1 (24) . Río Paragua off-shoot stream at RaudalAuraima (6°17’N, 63°37’W), B. Stergios, 19 May 1987, MCNG 18113 , 1 (40) . Departamento Sucre, río Caura, above Caño La Prision (7°00’N, 64°40’W), D. C. Taphorn et al., 1989, MCNG 21571 , 3 (22-25) ; USNM 375960 , 2 (22-23; formerly MCNG 21571 , in part) . Non-type specimens. 34 specimens (20-42.6 mm SL). Brazil. Roraima: Estrada between Fé (= Santa Fe , approximately 3°46’59"N, 59°35’59"W) and Esperança, INPA 16693 , 2 . rio Mucajaí, Cachoeira Paredão (approximately 2°57’N, 61°27’W), INPA 16694 , 2 (38-40) ; INPA 6505 , 2 (41.4-42.6) . Colombia. Meta: río Yucao , 13.5 km SE of Puerto Gaitan (4°23’N, 72°04’W), UF 26156 , 17 (19-29; 2 specimens, 25-27 mm, cleared and stained) . Río Manacías , sandbar on left (W) bank, 7 km SSE of Puerto Gaitan, AUM 28769, 1 (24) . Venezuela. Amazonas: río Ocamo below Arata rapids (3°08’N, 64°34’W), MCNG 23748 , 1 (31) . río Orinoco at Isla Cupaven (approximately 3°05’N, 67°40’W), FMNH 104482 , 1 (37) . Río Mavaca , 30 minutes upriver of base camp, at sand beach, AMNH 91375 , 1 (41) . Apure: Caño Potrerito at highway bridge between San Fernando de Apure and Puerto Paez (6°33’N, 67°16’W), INHS 27681 , 1 (21.5).

The following lot is tentatively identified as Cetopsidium pemon (see comments under “Remarks” above): Venezuela. Bolivar: Chimanta-tepui, río Abacapa , camp 1, 1300 m elevation (approximately 5°18’N, 62°10’W), FMNH 45708 , 4 (23-30; 1 specimen, 27 mm, cleared and stained) .

Figures

Fig. 2. Map of central and northern South America showing geographic distribution of Cetopsidium ferreirai (1 = holotype locality), Cetopsidium minutum (2 = holotype locality of Hemicetopsis minutus), Cetopsidium morenoi, Cetopsidium orientale (3 = holotype locality of Pseudocetopsis orientale), Cetopsidium pemon (4 = holotype locality), and Cetopsidium roae (5 = holotype locality) (some symbols represent more that one locality and/or lot of specimens).

Fig. 8. Cetopsidium pemon, new species, holotype, mature male, MCNG 19475, 25 mm SL; Venezuela, Bolivar, río Caroni at mouth of río Claro (7°54’45"N, 63°02’35"W).

Fig. 9. Cetopsidium pemon, new species, mature male,AMNH 91375, 41 mm SL; Venezuela, Amazonas, río Mavaca.