Denticetopsis iwokrama, 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 : 208-210

Denticetopsis iwokrama , new species

Figs. 46-47 , Tables 16-22

Diagnosis. Denticetopsis iwokrama can be differentiated from D. royeroi and D. sauli by the combination of the lack of elongate, symphyseal teeth on the dentary, the possession of a lateral line extending posteriorly beyond the abdomen at least onto the caudal peduncle, the presence of dentition on the vomer, a dorsal fin with 5 or 6 rays and with the first ray that is spinous basally, the symmetrical, shallowly-forked caudal fin, and the possession of horizontally-elongate, stellate, dark chromatophores when the chromatophores are expanded. Denticetopsis iwokrama differs from D. epa in the number of caudal (32 versus 26 to 28, respectively), preanal (17 versus 14 or 15, respectively), and total vertebrae (43 versus 38 to 40, respectively), and in the number of total anal-fin rays (29 versus 25 to 27, respectively). Denticetopsis iwokrama differs from D. macilenta in the number of caudal (32 versus 28 to 30, respectively), preanal (17 versus 14 to 16, respectively), and total vertebrae (43 versus 40 or 41, respectively), the position of the middle of the orbit (located at anterior 0.25 of HL versus 0.18-0.19 of SL, respectively), and in the width of the head as a proportion of the length of the head (head width/HL 0.72 versus 0.77-0.84, respectively). Denticetopsis iwokrama differs from D. praecox in the number of caudal (32 versus 27 to 30, respectively), preanal (17 versus 14 to 15, respectively), and total vertebrae (43 versus 38 to 41, respectively), and in the pigmentation of the caudal fin (without a distinct, pale region in the distal portions of the middle fin rays versus with a pale region in the distal portions of the middle fin rays, respectively). Denticetopsis iwokrama differs from D. seducta in the number of caudal (32 versus 26 to 31, respectively), preanal (17 versus 14 to 17 with 17 in only 1 of 23 specimens, respectively), and total vertebrae (43 versus 39 to 42 with 42 in only 1 of 31 specimens, respectively), and in the pigmentation of the pectoral fin (lightly pigmented versus heavily pigmented, respectively).

Description. Body moderately-elongate, slightly-compressed laterally anteriorly and becoming progressively distinctlycompressed posteriorly. Body depth at dorsal-fin origin approximately 0.23-0.25 of SL, and slightly longer than distance from anterior margin of orbit to posterior margin of opercle. Lateral line on body complete, unbranched, and midlateral; and extending from vertical through pectoral-fin base to caudal peduncle but falling short of posterior margin of hypural plate. Dorsal profile of body slightly convex from nape to dorsal-fin origin and straight from dorsal-fin origin to caudalfin base. Ventral profile of body slightly convex along abdomen, approximately straight, but posterodorsally-slanted, along base of anal fin. Caudal-peduncle depth nearly 1.4 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 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 slightly greater than distance from tip of 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 0.27 of HL. Eye diameter approximately one-half of snout length. Interorbital width slightly greater than 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 and ventral of horizontal extending through tip of snout. Distance between anterior nares slightly greater than 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 premaxillae, with third irregular row situated anterior to other tooth rows on medial portion of premaxilla. Vomerine teeth arranged in single, arched row with small gap in tooth series at midline. Vomerine teeth stout, conical, and becoming progressively larger in lateral portion of tooth row, but with even smallest teeth on vomer much larger than teeth present on premaxilla. Dentary teeth comparable in shape to, but larger in size than, premaxillary teeth. Dentary dentition arranged in irregular patch, with three rows of teeth medially that taper to one tooth row laterally.

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

Dorsal fin moderately large overall with length of dorsalfin base approximately 0.32-0.34 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 its length and flexible more distally, and lacking distal filament present in some species of Cetopsinae . Distal margin of dorsal fin convex, with second branched ray longest. Dorsal-fin origin located at approximately anterior 0.29-0.31 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 body.

Caudal fin shallowly-forked, symmetrical; tips of lobes rounded. Length of longest caudal-fin ray approximately 1.4 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. Membranous attachment present between posterior margin of basal two-thirds 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 posterior of vertical through posterior terminus of base of dorsal fin. Tip of adpressed pelvic fin extending past middle of SL to 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 and proportionally short with length approximately one-half that of first branched ray.

Coloration in alcohol. Overall coloration of most of head and body dark, but only slightly darker dorsally. Abdomen pale. Dark coloration primarily formed of large, stellate, horizontally-elongated chromatophores when chromatophores expanded. Compressed chromatophores appearing as discrete dark specks. Head dark dorsally, more so on snout, with dark pigmentation extending as far ventrally as horizontal extending through rictus of mouth. Head pale ventrally except for broad, dusky region around lower lip.

Dorsal fin dark on basal one-half except for pale anterior and posterior most rays; distal one-half of fin pale except for scattered, dark pigmentation on distal portions of middle fin rays. Anal fin with scattered, dark pigmentation somewhat more concentrated basally. Caudal fin largely pale except for dusky region basally. Pelvic fin pale, without dark chromatophores. Pectoral fin with few scattered, dark chromatophores basally.

Maxillary barbel dusky basally and pale distally. Mental barbels pale.

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

Distribution. Denticetopsis iwokrama is only known from the type locality in the Siparuni River basin, Guyana ( Fig. 46 ). Etymology. The specific name, iwokrama , is in reference to the Iwokrama rainforest project in the region of Guyana from which the holotype of the species was collected. It is a noun in apposition.

Remarks. Denticetopsis iwokrama is most similar to D. seducta , a species of the central and western portions of the Amazon basin. The two species demonstrate a distinct difference in the number of caudal and total vertebrae (see Tables 21, 22) and the pigmentation pattern of the pectoral fin and we consequently recognize them as different despite the limited available sample of D. iwokrama .

Material examined. 1 specimen (43 mm SL). Holotype. Guyana. Essequibo: Siparuni River at Tumble Down Creek, Essequibo River basin (4°48’39"N, 58°51’11"W), G. Watkins et al., 8 December 1997, ANSP 177215 , 1 (43).

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. 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).