Cetopsis arcana, 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 : 153-155

publication ID

https://doi.org/ 10.1590/S1679-62252005000200001

persistent identifier


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scientific name

Cetopsis arcana

new species

Cetopsis arcana , new species

Figs. 12 View Fig , 13 View Fig , Tables 9 -15

Pseudocetopsis plumbeus [not of Steindachner, 1882].– Bichuette & Trajano, 2003: 1105, 1108 [ Brazil, São Domingos karst region of upper rio Tocantins basin; presence in epigean and subterranean water systems].

Diagnosis. Cetopsis arcana can be distinguished from all of its congeners by the combination of the presence of an eye, the conical teeth on the vomer and dentary, the rounded posterior nares that is distinctly separated from the contralateral nares by a distance greater than the width of posterior nares, the presence of a dark humeral spot except in some individuals that lack a pattern consisting of dark pigmentation on the pectoral and pelvic fin other than for a thin, clear margin, the presence of a posteriorly-rounded, variably-developed, bilobed patch of dark pigmentation at the base of the caudal fin, the presence of a spot of dark pigmentation on the base of the dorsal fin with prominent dark pigmentation along the membrane behind the first ray of the dorsal fin, the possession of typically 42 or 43 total vertebrae (41 vertebrae in only one individual), the presence of a distinct demarcation between the dark pigmentation on the dorsal and dorsolateral surfaces of the body versus more ventral regions, and the limitation of eye-size or larger dark spots on the lateral surface of the body to the region dorsal of the horizontal extending through the ventral margin of the caudal peduncle.

Description. Body somewhat deep, slightly-compressed laterally anteriorly, becoming increasingly compressed posteriorly. Body depth at dorsal-fin origin slightly less than HL and slightly greater than 0.27 of SL. Lateral line on body complete, unbranched, and midlateral; extending from vertical through pectoral-fin base to hypural plate. Dorsal profile of body slightly convex and distinctly 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 posterodorsally slanted along base of anal fin. Caudalpeduncle depth slightly less than caudal-peduncle length.

Head coming to blunt point anteriorly and triangular overall in lateral view. Dorsal profile of head convex from tip of snout to vertical through posterior nares, straight from nares to vertical through middle of eye and convex from that point to posterior of nape. Ventral profile of head gently convex. Profile of snout in dorsal view triangular overall but rounded at tip. Portion of head posterior of nares with lateral profiles diverging from dorsal view. Dorsal surface of posterior portion of head with enlarged jaw musculature externally apparent.

Opercular membrane attaching to isthmus until point slightly anterior of vertical through pectoral-fin insertion. Opercular opening moderately wide; extending ventral of pectoral-fin insertion by distance approximately equal to snout length and extending dorsal of pectoral-fin insertion by distance approximately equal to two-thirds of snout length.

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-fourth of HL. Eye diameter approximately one-third of snout length. Interorbital width approximately equal to 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 point slightly ventral of tip of snout and along running through maxillary-barbel origin. Distance between anterior nares approximately equal to distance from anterior to posterior nares, and approximately equal to snout length. Posterior narial opening moderately large and located near dorsal profile of head and anterior to vertical through anterior margin of eye; opening rounded, with anterior two-thirds of aperture bordered by flap of skin and flap highest anteriorly. Distance between posterior nares slightly less than distance between anterior nares.

Mouth subterminal; its width approximately one-half of HL. Margin of lower jaw broadly rounded, its posterior extent reaching slightly beyond vertical through posterior margin of eye. Premaxillary tooth patch elongate, continuous across midline; anterior margin convex, posterior margin concave and running in parallel to anterior margin. Teeth on premaxilla of moderate size, conical, and sharply-pointed, with teeth arranged in four relatively regular rows medially and three relatively regular rows laterally. Teeth of anterior tooth row much smaller than teeth of remaining tooth rows, all of which are of similar size. Vomerine teeth arranged in one continuous, anteriorly-convex row. Vomerine teeth bluntly conical and distinctly larger than premaxillary teeth. Dentary dentition consisting of four irregular rows of teeth medially and reduced to two rows laterally and finally one row posteriorly. Teeth of outermost dentary tooth row distinctly smaller than teeth in other rows.

Maxillary barbel slender, its length distinctly greater than distance from tip of snout to posterior margin of orbit and nearly equal to one-half of HL; barbel origin at vertical through middle of eye. Mental barbels approximately equal in size and length and as long as maxillary barbel. Medial mental-barbel origin located along vertical through posterior margin of orbit. Lateral mental-barbel origin situated 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 0.45-0.48 of HL and slightly longer than distance from tip of snout to posterior margin of eye. Longest dorsal-fin ray, excluding distal filament on first ray, approximately equal to one-fifth of SL. Dorsal-fin spinelet absent. First dorsal-fin ray not spinous, with short, distal, filament in females and immature males and with longer filament in mature males. Distal margin of dorsal fin straight to distinctly concave, with first ray longest. Dorsal-fin origin located at approximately anterior one-third of SL and along vertical through middle of adpressed pectoral fin. Tip of adpressed dorsal fin, without filament, reaching to vertical through tip of adpressed pelvic fin. Posterior most dorsal-fin ray without posterior, membranous attachment to body.

Caudal fin moderately-forked, symmetrical; tips of lobes slightly rounded. Length of longest caudal-fin ray slightly more than 1.5 times length of middle fin rays.

Base of anal fin moderate, approximately 0.30-0.32 of SL. Anal-fin origin located distinctly posterior of middle of SL but anterior to middle of TL.Anal-fin margin straight in juveniles and presumed females, with posterior most unbranched anal-fin ray longest and subsequent rays gradually becoming shorter. Posterior most anal-fin ray with posterior, membranous attachment to body for basal one-fourth of its length. Anal-fin margin in mature males convex for anterior two-thirds and straight posteriorly, with rays along straight section slightly shorter than those of immediately preceding portion of fin.

Pelvic fin moderate, its distal margin slightly convex, with first branched ray longest. Tip of adpressed pelvic fin extending distinctly beyond middle of SL. Origin of pelvic fin located along vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin barely reaching vent. Medial most pelvic-fin ray with membranous attachment to body for basal two-thirds of its length.

Pectoral-fin length approximately two-thirds of HL. Margin of branched pectoral-fin rays straight along four lateral most rays with first ray longest and concave medially. First pectoral-fin ray not spinous and with distal filament in all specimens, but with filament proportionally longer in adult males.

Coloration in alcohol. Body very dusky dorsally and typically becoming abruptly pale in region of lateral line. Ventral half of body with irregular, dark, blotches of size slightly smaller than eye. Irregular blotches present in most individuals obscured in intensely pigmented specimens by overall darker pigmentation. Some exceptionally intensely pigmented specimens with dark pigmentation on ventrolateral portion of body nearly as well-developed as coloration on dorsal surface of body. Some specimens with distinct humeral spot. Ventral surface of abdomen pale in all specimens. Head dark dorsally and either pale or noticeably lighter ventrally. Dorsal surface of snout dark at least as far ventrally as horizontal extending through anterior nares, with dark pigmentation in some specimens extending anteriorly to dorsal margin of upper lip. Triangular region between upper lip and tip of snout pale or noticeably lighter than remainder of snout. Eyes with horizontally-elongate, ovoid, pale patch extending from vertical through anterior nares to vertical through lateral mental-barbel origin; more lightly-pigmented region less obvious in overall distinctly-darker individuals. Ventral surface of head pale or with some widely scattered spots of dark pigmentation.

Dorsal fin dark on basal one-half of anterior rays and basal one-third of posterior rays. Distal portion of dorsal fin clear or dusky, with abrupt, but irregular transition between dark and clear regions. Anterior margin of anal fin pale to base; with interradial membrane between first and second anal-fin rays dusky nearly to distal margin of fin. Dark, diffuse, pigmentation on anal fin extending along entire length of base and continuing onto fin rays to variable extent. Darkly-pigmented specimens with only distal margin of anal fin pale. Caudal fin with irregular, dark pigmentation forming bilobed patch of dark pigmentation at base of fin. Dark, bilobed patch variably obscured in darkly pigmented specimens. Caudal fin with scattered, dark pigmentation along at least basal portions of rays, with small spots of dark pigmentation extending nearly to distal margin of fin in darkly-pigmented specimens. Pelvic and pectoral fins generally pale, with scattered, dark chromatophores at base of fins and on dorsal surface of interradial membrane between first and second rays.

Barbels dusky basally and becoming pale distally.

R. P. Vari, C. J. Ferraris Jr.& M. C. C. de Pinna 155

Sexual dimorphism. Mature males of Cetopsis arcana have the distal filament on the first rays of the dorsal and pectoral fins somewhat more developed than those present in females and immature males. The anal-fin margin in males of the species is convex overall with abruptly shorter posterior rays, contrary to being straight in females and immature males.

Distribution. Cetopsis arcana is only known from middle and upper portions of the rio Tocantins basin ( Fig. 12 View Fig ).

Etymology. The species name, arcana , from the Latin for secret or hidden, refers to the occurrence of the species in sinkholes in the type region.

Ecology. The type series of Cetopsis arcana was collected in a karstic region of the upper rio Tocantins basin in both epigean and subterranean waters (Bichuette & Trajano, 2003: 1105, 1108; species cited therein as Pseudocetopsis plumbeus ).

Remarks. One relatively small specimen with a reported locality of Brazil, Roraima, rio Oraricao, Igarapé Canao (approximately 4°46’N, 60°24’W) in the rio Branco basin, with limited remaining dark pigmentation on the head and body (INPA 1860; 46 mm SL), is apparently a member of the complex of species of Cetopsis characterized by the presence of a bilobed patch of dark pigmentation at the base of the caudal fin. Additional material is necessary to determine whether that specimen represents a range extension for C. arcana , another species of that complex, or an undescribed form.

Material examined. 19 specimens (23-90 mm SL). Holotype. Brazil. Goiás: São Domingos, Parque Estadual de Terra Ronca, Boca da Lapa de Bezerra (13°32’43"S, 46°22’35"W), A. Akama, 24 July 1999, MZUSP 58637 View Materials , 1 View Materials (76) GoogleMaps . Paratypes. 8 specimens (8, 45-90 mm SL). Brazil. Goiás: São Domingos, sumidouro (sinkhole) of rio da Lapa, Parque Estadual de Terra Ronca , approximately 100 m from sinkhole, M. E. Bichuette & R . dos Santos , 19 July 1999, MZUSP 55965 View Materials , 3 View Materials (69-90, 1 specimen, 85 mm, cleared and stained) ; USNM 372765 View Materials , 1 View Materials (67) . Arroio Arara, 500 m from mouth of rio Maranhão in Rosariana (14°01’S, 48°25’W), R GoogleMaps . E. Reis et al., 14 July 1992, MCP 16002 View Materials , 1 View Materials (86) . rio Tocantins, Córrego Agua Boa, upstream of dam of Serra de Mesa (13°34’S, 48°14’W), MHNG 2593.99 View Materials , 1 View Materials (47) GoogleMaps . Córrego Taquaral, left bank tributary of rio das Almas , of rio Maranhão, upper Tocantins (14°38’S, 49°9’30"W), G. W. Nunan & D. F. Moraes, 4 October 1985, MNRJ 12772 View Materials , 1 View Materials (83) GoogleMaps . Rio Tocantins, at site of future dam of Usina Hidroeléctrica Serra da Mesa (13°33’S, 48°14’W), D. F. Moraes et al, July 1988; MNRJ 16942 View Materials , 1 View Materials (45) GoogleMaps . Non-type specimens. 10 specimens (23- 54.5 mm SL). Brazil. Mato Grosso: rio Araguaia basin, creek tributary to ribeirão Lajeadinho, below the ferry, MZUSP 41462 View Materials , 1 View Materials (54.5) . Município Alto Araguaia, rio Taquari basin, Fazenda Córrego do Mato , córrego do Mato , MZUSP 41492 View Materials , 6 View Materials (23-49; 2 specimens, 35-43 mm, cleared and stained) . Pará: rio Itacaiunas, Caldeirão , igarapé do Pojuca (5°45’S, 50°30’W), MZUSP 31432 View Materials , 1 View Materials (50) GoogleMaps . Rio Tocantins, Tucuruí , INPA 13004 View Materials , 1 View Materials (24) . Rio Tocantins, above Tucuruí , INPA 6504 View Materials , 1 View Materials (35).


Departamento de Geologia, Universidad de Chile


Pontificia Universidade Catolica do Rio Grande do Sul