Odontostilbe pao, Bührnheim & Malabarba, 2007

Bührnheim, Cristina M. & Malabarba, Luiz R., 2007, Redescription of Odontostilbe pulchra (Gill, 1858) (Teleostei: Characidae: Cheirodontinae), and description of two new species from the río Orinoco basin, Neotropical Ichthyology 5 (1), pp. 1-20 : 16-18

Odontostilbe pao , new species

Fig. 23

Holotype. MCNG 54497 , 1 (male 29.3 mm SL), Venezuela, Cojedes, río Pao at el Caserio, El Pueblito, D. Taphorn et al., 28 July 1985.

Paratypes. MCNG 54107 (4 males 27.2-28.5mmSL) ; MCP 40976 (1 male 28.7 mm SL, 1 male 28.8 mm SL), same data as the holotype .

Diagnosis. Odontostilbe pao differs from the two other species from the río Orinoco basin, by the presence of a remarkable elongation of the 2 nd unbranched dorsal-fin ray in males, not found in males of O. pulchra ( Fig. 1 ), and short in males of O. splendida .Additionally, males of O. pao are distinguished from the two other Orinoco species by the longer snout length ( O. pao 26.7-30.6% HL, O. pulchra 18.0-26.0% HL, O. splendida 24.1-26.9% HL) ( Figs. 5 , 26 ), and longer upper jaw length ( O. pao 32.5-34.7% HL, O. pulchra 27.1-31.8% HL, O. splendida 29.1-31.5% HL) ( Fig. 26 ). The presence of hooks on 1 st to 8 th anal-fin branched rays separates O. pao from O. pulchra (hooks on 1 st to 22 th anal-fin branched rays). The gill raker counts on lower branch (averaging 11) differ from O. fugitiva (usually 12) ( Fig. 18 ). Odontostilbe pao differs from all other Odontostilbe species by the peculiar shape of the posterior portion of the maxilla, somewhat triangular, short, with midlength portion deeper and gradually narrowing to the posterior tip ( Fig. 24 ), vs maxilla somewhat spatula-like shaped, short or elongate, with a deep midlength and posterior region, and then narrowing abruptly only at posterior tip in all other Odontostilbe species ( Figs. 6 , 19 ).

Description. Only males available. Morphometric data are given in Table 3 . Largest male reaching 29.3 mm in SL. Body elongated and compressed. Greatest body depth at dorsalfin origin. Snout pointed. Head profile gently convex to straight from snout to posterior tip of supraoccipital bone. Predorsal profile slightly convex between tip of supraoccipital bone and dorsal-fin origin, then straight from dorsal-fin origin to caudal peduncle. Ventral profile convex from mouth to anal-fin origin. Anal-fin base straight. Caudal peduncle slightly longer than deep.

Head relatively small. Posterior margin of opercle sinusoidal with upper portion concave and lower portion convex. Snout pointed. Mouth terminal, premaxilla projects beyond dentary leaving border of teeth cusps exposed. Maxilla obliquely positioned ending at vertical on anterior eye border, and at horizontal slightly below inferior eye border. Premaxillary teeth 6, bearing 8-10 cusps; central cusp longest ( Fig. 24 ). Maxilla with 4 similar teeth bearing 3-7 cusps, decreasing cusp number to posterior tip of maxilla. Dentary teeth 11 bearing 1-7 cusps, gradually decreasing in size, first 7 teeth largest with 6-7 cusps, 1 medium-sized tooth with 5 cusps, and last small teeth conical or with 2 cusps. Smaller cusps of dentary teeth overlap cusps of adjacent tooth.

Dorsal-fin rays ii,9 (7). Dorsal fin slightly behind mid length of body, and slightly posterior to pelvic-fin origin. Second unbranched dorsal-fin ray elongate in males, extending beyond dorsal-fin distal profile. Anal-fin rays iv(1), v (6), 18 (1), 19(2), or 20(4). Anal-fin distal border concave. Pectoral-fin rays i(7), 10 (2), 11(4), or 12(1). Pelvic-fin rays i (7), 6i (2), 7 (5). Unbranched pelvic-fin ray longest in mature males, extending beyond origin of anal fin. Lateral skin border of unbranched pectoral-fin ray and unbranched pelvic-fin ray slightly thickened in males. Principal caudal-fin rays 19 (7). Procurrent caudal-fin rays: dorsal 11(3), or 12 (4), ventral 9(1), 10(4), or 11 (2). Caudal-fin ray flaps ventrally on 4 th- 7 th branched rays of upper lobe, and dorsally on 13 th -15 th branched rays of lower lobe. Adipose-fin at vertical through last anal-fin ray insertion.

Males with acute, elongate, retrorse hooks on posterior border of pelvic- and anal-fin rays. One or two paired and unpaired hooks per segment on last unbranched anal-fin ray, and 1 st to 8 th (mostly 6-7 th) anal-fin branched rays, mid positioned on fin rays. One or two unpaired slender hooks per segment on 1 st to 7 th branched pelvic-fin rays, extending almost entirely and reaching end tip of fin rays.

Scales cycloid: lateral line complete about 36 (scale insertions counted when scale is lacking); predorsal row 10(1), or 11 (2); scale rows between lateral line and dorsal-fin origin 6 (6), or 7(1); scale rows between lateral line and anal-fin origin 4 (4); scale rows around peduncle missing. Triangular modified scale on pelvic-fin base extends posterior covering 2 scales.

Cleared and stained specimens (1): supraneurals 4; precaudal vertebrae, including Weberian apparatus, 16; caudal vertebrae 18; gill rakers, upper 6, lower 11 (2 on hypobranchial). Alcohol specimens (6): gill rakers, upper 6 (6), lower 10(1), or 11 (5). Upper gill rakers with none to 2 denticles on anterolateral border, and none on posterolateral border; lower gill rakers with none or 2 denticles on anterolateral border, and none or 1 denticle on posterolateral border; posteriormost lower gill raker with just 3 denticles on anterolateral border ( Fig. 25 ). Denticulation mainly on basal portion of gill rakers.

Sexual dimorphism. Only mature males available, presenting typical dimorphic characters found in other Odontostilbe species, like the presence of hooks on pelvic- and anal-fin rays, and the elongation of dorsal- and pelvic-fin rays. The gill gland is present on the first gill arch including 7 to 9 anterior branchial filaments ( Fig. 25 ). Snout well-developed in males, and probably a dimorphic character as found in other Odontostilbe species (Bührnheim & Malabarba, 2006). Color in alcohol. General ground body color beige. Dorsal part of the body from head to peduncle darker with chromatophores more concentrate on scales border. Dark chromatophores along all dorsal-fin rays. Pectoral fin with chromatophores along 1 st unbranched pectoral-fin ray and 1 st branched fin rays. Pelvic fin hyaline.Anal fin with dark chromatophores on more central branched anal-fin rays, except at the tips of the last unbranched fin rays and the 1 st branched fin ray; hyaline in holotype. Adipose fin clear. Caudal fin almost entirely covered with diffuse chromatophores along fin rays, except clearer areas on base of caudal-fin lobes just behind caudal-fin spot (chromatophores very faded in type material). Rounded black to brown spot on the base of caudal fin, reaching upper border of caudal peduncle.

Chromatophores on snout, upper lip, proximal portion of maxilla, infraorbitals 1, 2. Pigmentation of top of head on frontals and parietals, with deep-lying chromatophores over brain membrane below frontals and parietals, and fontanels. Faint dark and silver midlateral stripe, beginning behind pseudotympanum, above lateral line, and reaching caudal spot. Guanine on eye iris, opercle, isthmus, and most of 3 rd infraorbital. Below lateral line body faint without pigmentation, a few chromatophores above anal-fin base in holotype.

Distribution. Only known from type locality río Pao, affluent of the río Chirgua-Guanare system, río Portuguesa, río Apure- Orinoco basin ( Fig. 22 ).

Etymology. Refers to the type locality río Pao.

Ecological notes. Type material was caught in the llanos, savannas, white water, together with the cheirodontines Cheirodontops geayi and Odontostilbe pulchra (Donald Taphorn pers. commun.).

Remarks. A principal component analysis with 17 morphometric variables grouped separately males of O. pao , O. splendida , and O. pulchra , except for one specimen of O. splendida , nearby O. pulchra specimens on the PC3 axis ( Fig. 26 ). PC2 was affected most strongly and negatively by snout length, dorsal-fin length, and upper jaw length; and positively by analfin base. Odontostilbe pao has longer snout length, dorsal-fin length, and upper jaw length as referred in its diagnosis. PC3 was affected most strongly and negatively by pectoral-fin length, and anal-fin base; and positively by depth at dorsal-fin origin, snout-anal fin origin, and caudal peduncle depth. Actually, O. pao and O. pulchra have smaller values for body depth at dorsal-fin origin, snout-anal fin origin, and caudal peduncle depth than O. splendida ( Tables 1-3 ). In contrast, males of O. pao , and O. pulchra have longer pectoral-fin length, anal-fin base, and caudal peduncle depth ( Tables 1-3 ). The specimen of O. splendida positioned far below has the highest proportion of anal-fin base 26.8 % in SL among all specimens measured, which explains its position nearly O. pulchra specimens. This specimen through regression analyses matched O. splendida characters. The pelvic-fin length was not considered in the principal component analysis because it increased the overlap between O. pulchra and O. splendida since pelvicfin length ranges are similar.

Figures

Fig. 23. Holotype of Odontostilbe pao, MCNG 54497, male 29.3 mm SL.

Fig. 1. Odontostilbe pulchra, syntype MNHN 0000-9593, female 28.7 mm SL (top), a specimen INHS 40101, male 32.3 mm SL from Trinidad(middle top), and specimensMCP 38863, male 28.6 mm SL (middle bottom), andfemale 32.5 mm SL (bottom) from río Orinoco basin.

Fig. 5. Snout length as a function of head length for males of Odontostilbe pulchra, against O. splendida, and O. pao.

Fig. 26. Principal component analysis of the 17 morphometric measurements of males of Odontostilbe pulchra (PU), Odontostilbe splendida (S), and Odontostilbe pao (PA). Stronger loadings on the second and third principal components (PC2, PC3).

Fig. 18. Lower gill rakers counts of Odontostilbe pulchra, Odontostilbe fugitiva (data from Bührnheim & Malabarba, 2006), and of two new species Odontostilbe splendida, and Odontostilbe pao.

Fig. 24. Dentition of Odontostilbe pao, MCNG 54107, male 28.8 mm SL c&s. Photograph of left side premaxilla (top), maxilla (middle), and dentary (bottom), lateral view, under estereosmicroscope.

Fig. 6. Dentition of Odontostilbe pulchra, INHS 40101, male 32.5 mm SL:left premaxilla (top), maxilla (middle), and dentary (bottom), lateral view. Scanning electron micrograph (SEM).

Fig. 19. Dentition of Odontostilbe splendida, paratypeANSP 181041, female 32.1 mm SL:right side premaxilla (top), maxilla (middle), and dentary (bottom), lateral view. Scanning electron micrographs (SEM).

Fig. 25. First gill arch of Odontostilbe pao, MCNG 54107, male 28.8 mm SL. SEM photographs of the first gill arch, left side, lateral view, showing gill gland (top), in detail gill rakers on upper branchial branch (middle), and gill rakers on lower branchial branch (bottom).

Fig. 22. Distribution of Odontostilbe splendida (triangles), and Odontostilbe pao (square). Symbols can represent more than one lot, and more than one locality.