Characidium chancoense, Agudelo-Zamora & Ortega-Lara & Taphorn, 2020

Agudelo-Zamora, Henry D., Ortega-Lara, Armando & Taphorn, Donald C., 2020, Characidium chancoense, a new species of South American darter from the Río Cauca drainage, Colombia (Characiformes: Crenuchidae), Zootaxa 4768 (2), pp. 249-263 : 250-260

Characidium chancoense , new species

( Figs. 1 , 2f , 3 ; Table 1)

urn:lsid:zoobank.org:act:DD25AADA-BFDC-46CA-88C9-37AA76784503

Characidium sp.— Roman-Valencia & Garcia, 2006:22, fig. 1A (morphogeometry; specimens from Zanjón Bagazal, Rio Cauca basin, Colombia; comparison with Characidium caucanum ).

Holotype. IMCN 4528 , 50.5 mm SL, Colombia, Valle del Cauca, Ansermanuevo, upper Río Cauca drainage, Río Chanco , 4°46’30.14”N 76°0’8.62”W, A. Ortega-Lara, 26 Nov 2000.

Paratypes. All from Colombia. Departamento Valle del Cauca, Río Cauca drainage: IMCN 4474, 11, 40.8–49.5 mm SL, Ansermanuevo, Río Chanco, 4°46’30.14”N 76°0’8.62”W, A. Ortega-Lara, 26 Nov 2000; IMCN 4527, 20 + 3 C&S, 34.7–44.6 mm SL, Ansermanuevo, Río Chanco, km 4 road to El Águila and the Ansermanuevo city, Bellavista farm, A. Ortega-Lara, 27 Nov 2000; IMCN 4823, 2, 44.9–45.2 mm SL, Ansermanuevo, Río Chanco, 4°46’30.14”N 76°0’8.62”W, A. Ortega-Lara, 26 Nov 2000; IMCN 4480, 3, 42.1–47.3 mm SL, Ansermanuevo, Río Chanco, 4°44’37”N 76°03’30”W, A. Ortega-Lara, 8 Nov 2000; IMCN 4530, 7, 40.3–49.2 mm SL, Ansermanuevo, Río Chanco, Bellavista farm, 4°46’30.14”N 76°0’8.62”W, A. Ortega-Lara, 26 Nov 2000; IMCN 4491, 3, 33.7–46.9 mm SL, Ansermanuevo, Río Chanco, 4°46’30.14”N 76°0’8.62”W, A. Ortega-Lara, 22 Nov 2000. Departamento Quindío: IUQ 3778, 2, 43.1–47.1 mm SL, Río Portugal de Piedras (upper Río Cauca drainage), 4°03’09.9”N 76°21’16.8”W, M. Ramírez and J. Arcila, 22 Oct 2008.

Non-types. All from Colombia, Río Cauca basin. CIUA 268, 1, 53.1 mm SL, Antioquia, Anorí, Quebrada Boquerón, tributary of Porce III dam, 7°0’29.02”N 75°3’51.98”W, A. Bermúdez, 03 Jun 2005; CIUA 705, 2, 42.6–48.4 mm SL, Antioquia, Barbosa, Quebrada Las Lajas at I-62 route, 6°28’16.2”N 75°17’29.9”W, J. G. Ospina-Pabón, 03 Jun 2007; CIUA 799, 1, 39.5 mm SL, Cauca, Buenos Aires, Río Cauca, near to Vereda La Balsa, 03°05’10.9”N 76°35’36.8”W, J. G. Ospina-Pabón and L. Ochoa, 01 Jan 2005.

Diagnosis. Characidium chancoense can be distinguished from its trans-Andean congeners, except females of C. caucanum , by its pigmentation pattern and internal morphology. It has a vertically elongate spot between the posterior edge of the opercle and the humeral blotch which abuts a yellow gap (live specimens) or white gap (preserved specimens) that ends at the humeral blotch, and 7–12 vertical bars that occupy completely the scales on which they occur; anteriormost 6–11 bars are cuneate shaped with their vertices reaching to, or one scale row below, the lateral-line scale series, posteriormost 1–4 bars (counted from the caudal-fin base) reach past the lateral line to the ventral margin of the caudal peduncle. Vertical bars are absent in males of C. caucanum , and present in C. sanctjohanni and C. cf. zebra but only occupy the scale margins, leaving the center unpigmented, creating a chain pattern. Characidium phoxocephalum has spots and vertical bars above, on and below the lateral stripe. Characidium chancoense lacks a well-defined dark caudal-peduncle spot but does have the middle caudal-fin rays pigmented only near their bases by the continuation of the lateral stripe, and the rest of the fin hyaline. In C. phoxocephalum and C. caucanum the middle caudal-fin rays are pigmented along their entire length. Characidium cf. zebra has a small, well-defined dark caudal-peduncle spot located slightly posterior to the caudal-fin base and the rest of the fin is hyaline ( Fig. 1 ). Characidium chancoense females differ from those of C. caucanum by the length and shape of the vertical bars (only the posterior bars cross the lateral line and they are not sinuous vs. vertical bars crossing the lateral line and sinuous) ( Fig. 2e, f ). Lastly, a review of Eigenmann’s (1922: 315) illustration of C. phoxocephalum and C. caucanum shows notable differences in the shapes of the caudal-fin lobes: a forked caudal fin with pointed lobes, which has also been confirmed by examination of topotypic specimens and which differs from the rounded caudal-fin lobes of C. chancoense ( Fig 1 , 2c, d, e .). See additional comments on the diagnosis of the species in the Discussion, below.

Description. Morphometric data given in Table 1. Body slightly compressed laterally. Dorsal profile moderately convex from snout to anterior naris, slightly convex from there to tip of supraoccipital, then moderately convex to dorsal-fin origin; roughly straight and posteroventrally inclined through dorsal-fin base to adipose-fin origin; slightly concave from latter point to first procurrent caudal-fin ray. Ventral profile moderately convex to pectoral fin insertion, then gently convex to anal-fin base; posterodorsally inclined along anal-fin, almost straight along caudal peduncle. Greatest body depth at or just anterior to dorsal-fin origin. Snout with rounded tip, at level of ventral margin of orbit. Maxilla relatively short, reaching posterior naris but not anterior margin of eye. Orbit circular, about equal to snout length; iris round.

Dorsal-fin rays ii+8 (3), ii+9* (48) or ii+10 (2); anal-fin rays ii+ 6+i (10) or ii+7+i* (43); pectoral-fin rays iii+10+i* (31), iii+11+i (20) or iii+12+i (2); pelvic-fin rays i+7 (6), i+8* (44) or i+9 (3); principal caudal-fin rays (upper and lowermost simple) i+8+7+i (2), i+8+8+i (2), i+8+9+i (13), i+9+8+i* (34) or i+9+9+i (2). Adipose fin present, situated at vertical through posterior end of anal-fin base.

Scales cycloid. Lateral line complete, pored lateral-line scales: 31(1), 34(7), 35*(7), 36(23), 37(14), 39(1). Scale rows above lateral line 3(1), 4*(52), and below lateral line 2*(37), 3(16). Scales around caudal peduncle 10(9), 11*(23), 12(21). Predorsal scales series arranged in single, regular row; scales in predorsal series 10(17), 11*(35), 12(1). Isthmus scaled.

Outer premaxillary tooth series with two bicuspid teeth and six (2) to seven (1) conic teeth ( Fig. 4a ). Maxilla edentulous. Dentary with ten (3) teeth, decreasing in size posterolaterally with posteriormost teeth only 1/3 the height of anteriormost; anteriormost five teeth tricuspid, remaining teeth conical ( Fig. 4b ). Gill rakers on ventral lobe of first gill arch numbering 9 (3), first two very small and rudimentary. Four branchiostegal rays.

Lower process of dentary with sensorial canal that begins at symphysis and extends to posterior tip. Posterior tip of dentary ending in sharp point. Anguloarticular triangular with base longer than unequal sides, upper vertex of articular truncate, anterior vertex pointed. Anguloarticular joint with quadrate concave with dorsally curved posterior process. Retroarticular elongate with rounded posterior margin, boot-shaped. Quadrate joint with anguloarticular rounded, postero-inferior process of quadrate articulating with symplectic and postero-superior process pointed; upper margin convex, anterior margin straight up to articulation. Metapterygoid butterfly shaped. Mesopterygoid shaped as inverted trapezoid. Ectopterygoid with 11+14 conical teeth (1) or 11+11 (1). Palatine rectangular. Maxilla with upper margin straight or slightly concave, lower margin convex with two antero-superior foramina; posterior tip rounded, anterior tip sharply pointed.

Dorsal lamina of mesethmoid bone considerably narrower anteriorly than posteriorly and attached to the frontal (see Buckup 1993b: 230); portion of mesethmoid contacting premaxila ending in three rounded lobes. Optic nerve foramen in pterosphenoid with opening oriented antero–posteriorly. Fontanel trapezoidal, bordered anteriorly by frontals, laterally by parietals and posteriorly by supraoccipital (one specimen with anterior margin forming vertex between parietals).

Vertebrae 36–38 (2). Ribs 17 (2). Dorsal fin with 10 (2) or 11 pterygiophores (1). Anal fin with eight (2) or nine (1) pterygiophores (1). Swimbladder with posterior chamber much longer than anterior chamber ( Fig. 5c ).

Color in alcohol. Overall color of head and body tan or yellowish-tan. Dorsal midline with faint brown stripe from tip of supraoccipital to dorsal-fin base, and from posterior margin of dorsal-fin base to adipose-fin origin. Dorsum with two additional, narrower stripes (sometimes broken into rows of tightly packed dots), one extending from rear of head to slightly posterior to dorsal-fin origin, the other from rear of head to adipose fin. Diffuse gray midlateral stripe originating on the upper lip and very faintly continuing posteriorly across the snout, eye, infraorbitals, and upper opercle, absent from the posterior opercular margin and anterior to well-defined, rounded humeral blotch posterior to upper margin of opercle. Dark, well-defined midlateral stripe extending from immediately behind humeral blotch to base of middle caudal fin rays (width approximately 7/8 of scale height). Stripe darkest where overlain by the 7–12 vertical, cuneate-shaped bars. In faded specimens bars fainter and tips of their vertices more noticeable. Dorsal fin dusky gray with band of pigment concentrated on rays passing through middle of fin. Adipose fin light proximally, dusky gray distally. Caudal fin with dark pigmentation concentrated on first three or four upper and lowermost procurrent rays and middle rays. Anal fin with irregular band of melanophores concentrated on membranes. Pelvic and pectoral fins hyaline or light yellow.

Color in life. Dorsum olivaceous from rear of head to caudal fin, venter white blending with reddish color (specimens from quebrada Dopo at finca Los Chorros, tributary of río Cauca, vereda los Chorros, Yotoco, Valle del Cauca) from base of pelvic fin to caudal fin. Fin rays yellowish, distal parts of fins hyaline. Iridescent band present under black lateral line located over lateral-line scales. Base of each caudal-fin lobe with olivaceous or reddish spots separated by black basicaudal spot ( Fig. 1b ). Sexual dimorphism. None observed.

Etymology. Named after its type locality, the Río Chanco. To be treated as a Latinized geographic adjective. Distribution. This species occurs in tributaries of the Río Cauca system, Cauca, Valle del Cauca and Antioquia

Departments, Colombia ( Fig. 3 ).

Figures

FIGURE 1. Characidium chancoense. a.) IMCN 4528, Holotype 50.5 mm SL; Colombia, Valle del Cauca, Río Chanco, tributary of Río Cauca. Scale bar: 1cm. b.) Live specimen (uncataloged).

FIGURE 2. Species of the genus Characidium present in the trans-Andean region of Colombia. a.) Characidium caucanum (holotype) FMNH 56057; b.) Characidium phoxocephalum (holotype), FMNH 56061; c.) C. caucanum, IUQ 563 (male); d.) C. phoxocephalum, IUQ 1250; e.) C. caucanum, IUQ 563 (female); f.) C. chancoense (holotype), IMCN 4528; g.) C. zebra (holotype), FMNH 53547; h.) C. sanctjohanni (holotype), ICN-MHN 211; i.) C. cf. zebra, SU 50391; j.). C. sanctjohanni, IMCN 8928; k.) C. cf. boavistae, UCO-P 409; l.) C. cf. boavistae, IMCN 2615.

FIGURE 3. Distribution map of the Characidium species in the trans-Andean region. Red-white-X circle: type locality of C. chancoense; gray circle: C. santjohanni; red triangle: C. phoxocephalum; blue triangle: C. cf. zebra; white circle: C.cf. boavistae; blue pentagon: C. caucanum; pink circle: C. chancoense. Some symbols corresponds to more than one species record.

FIGURE 4. Medial view of (a.) left premaxilla and (b.) dentary of Characidium chancoense, IMCN 4527, paratype. Scale bar: 0.2 mm.

FIGURE 5. Swimbladder shape of the Characidium species from the Río Cauca drainage. a.) Characidium caucanum, IMCN 4529 (44.3 mm. SL); b.) C. phoxocephalum, IMCN 4529 (77.7 mm. SL); c.) C. chancoense, IMCN 4527 (45.2 mm. SL) and d.) C. cf. zebra, IUQ 945 (39.9 mm. SL). Scale bar: 1 mm.