Odontostilbe ecuadorensis, Bührnheim & Malabarba, 2006

Bührnheim, Cristina M. & Malabarba, Luiz R., 2006, Redescription of the type species of Odontostilbe Cope, 1870 (Teleostei: Characidae: Cheirodontinae), and description of three new species from the Amazon basin, Neotropical Ichthyology 4 (2), pp. 167-196 : 179-183

Odontostilbe ecuadorensis , new species Fig. 14

Holotype. ANSP 170608 , 1 (male 45.7 mm SL), Ecuador, Napo, Santa Cecilia, río Aguarico , 00°06’N 76°51W; W. G. Saul & F. B. Cross, 14 Jun 1968.

Paratypes. ECUADOR, SUCUMBÍOS: ANSP 130574 , 12 m (1 male 45.6 mm SL, 9 females 42.7-46.7 mm SL, 1 female 49.1 mm SL c&s, 1 unsexed 35.1 mm SL), backwater of río Aguarico at Santa Cecilia , 00°06’N 76°51’W, W. G. Saul, 30 Jun 1967 . MCP 38419, 12 m (5 males 32.7-38.6 mm SL, 1 female 40.1 mm SL, 6 unsexed 24.1-36.2 mm SL), río Napo, beach on south bank, 2.7 km upstream from bridge at Coca , 00°29’S 77°24’W, D. Stewart, M. Ibarra, R. Barriga & Uquillas, 2 Oct 1981 . FMNH 113512 , 74 unsexed (4 males 32.4-33.4 mm SL, 70 unsexed 28.6-35.0 mm SL) , same data as MCP 38419. KU 13524 , 15 m of 32 (7 males 36.3- 45.8mm SL, 2 males 43.3 mm SL and 43.5 mm SL c&s, 2 females 41.7 mm SL and 45.2 mm SL, 1 female 45.2 mm SL c&s, 3 unsexed 33.6-34.8 mm SL), Aguarico, isolated pool at backwater of río Aguarico at Santa Cecilia, W. G. Saul, 27 Jun 1968 . KU 13526 , 3 m (1 male 44.0 mm SL, 2 females, 47.7-50.2 mm SL), río Aguarico at Santa Cecilia, W. G. Saul, 13 Mar 1967 . MEPN 1517 , 2 m (1 female 45.2 mm SL, 1 female 43.6 mm SL c&s), Sucumbíos, río Duguno, 2 km on south of indian group Cofán del Duguno, Aguarico [drainage], 00°08’15"N 76°45’18"W, R. Barriga & S. Criollo, 1 May 1995 . ECUADOR, NAPO: FMNH 113511 , 1 m (7 males, 38.2- 45.5 mm SL), río Napo, cocha of mainstream, at and 1.2 km downstream from mouth of río Suyunoyacu (ca. 16 km from Coca ), 00°32’36’’S 77°04’54’’W, 22 Sep 1981 . FMNH 113513 , 11 m (unsexed 29.6-32.5 mm SL), río San Miguel at Tipishca , km 54.5, [upper río Putumayo], 00°12’30’’S 76°13’ W, D. Stewart, M. Ibarra & R. Barriga., 4 Oct 1983 . FMNH 113514 , 5 m (4 males 40.6-43.2 mm, 1 male 43.5 mm SL c&s, 1 female 40.3 mm SL), Napo, quebrada Capihuara, distributary of río Payamino , [río Coca, río Napo drainage], 00°30’S 76°14’30’’W, D. Stewart, M. Ibarra & R. Barriga., 13 Nov 1983 .

Non-type material. Río Napo basin, ECUADOR, SUCUMBÍOS: ANSP 141496 , 2 m (unsexed 27.8-28.8 mm SL), [ río Pañayacu ], 00°25’S 76°07’W . ANSP 141506 , 12 m (unsexed 27.0- 31.2 mm SL), Napo, near mouth of río Cuyabeno , 00°16’S 75°53’W . ECUADOR, NAPO: ANSP 141508 , 1 m (female 36.0 mm SL), mouth of río Shushu Fundi , 00°18’S 76°21’W . PERU, LORETO, MAYNAS, ARCADIA: USNM 379440 , 1 (unsexed 28.5 mm SL), middle río Napo , Padre Isla, cocha Chica. USNM 379469 , 1 (unsexed 21.2 mm SL), middle río Napo quebrada Negra 1, en la quebrada Norte. USNM 384420 , 1 (unsexed 22.3 mm SL) , same data as USNM 379440. USNM 384822 , 1 (unsexed 18.0 mm SL), río Napo , cocha de Conchas . PERU, LORETO, MAYNAS, CASTANA: USNM 328553 , 5 (unsexed 17.0- 18.1 mm SL), middle río Aguarico, quebrada Castana Negra. Lower río Napo , PERU, LORETO: ANSP 178148 , 2 m (unsexed 33.7 -40.9 mm SL), Maynas, beach & backwater along right bank just upstream from mouth río Mazán , near town of Mazán, 03°29’10’’S 73°06’24’’W . INHS 36600 , 2 m (unsexed 30.4-32.0 mm SL), mouth of río Mazán, near town of Mazán. INHS 36658 , 1 m (unsexed 37.6 mm SL), 1 km upstream mouth of río Mazán , 3 km west town of Mazán. INHS 36668 , 1 m (unsexed 30.6 mm SL), 1 km upstream mouth of río Mazán , 3 km west town of Mazán .

Diagnosis. Characters that diagnose Odontostilbe ecuadorensis are: (1) upper gill rakers 5-6, lower 9-11, mostly 10-11 (vs. upper gill rakers 6-8, mostly 6-7, and lower 11-14, usually 12 in O. fugitiva ( Fig. 13 a-b); (2) denticulation of gill rakers more numerous in O. ecuadorensis than in O. fugitiva (in specimens larger than 32.5 mm SL), mainly on posteriormost gill raker of lower arch (5-6 denticles on basal portions of gill raker in O. ecuadorensis vs. 0-2 in O. fugitiva ( Figs. 3 , 16 ); (3) elongate 2 nd unbranched dorsal-fin ray (vs. not elongate in O. euspilura and very short elongate in O. pulchra ); (4) no hooks on unbranched pelvic-fin ray (vs. 1-2 unpaired hooks per segment on 1 st unbranched pelvic-fin ray occasionally present in O. euspilura and O. pulchra ); (5) 1-3 paired or unpaired hooks per segment on last unbranched anal-fin ray, and 1 st to 16 th anal-fin branched rays (small hooks like knots on anal-fin ray branches, usually on 10 th branched fin ray and following rays) (vs. well-developed hooks on 1 st to 22 nd anal-fin branched rays at distal half length of fin rays in O. pulchra ); and (6) usually seven large dentary teeth, with seven cusps (vs. 4 large dentary teeth with 3 large and compressed central cusps and 2, 3 lateral small cusps in O. pequira ). Odontostilbe ecuadorensis differs from sympatric O. euspilura by its terminal mouth (vs. subterminal mouth).

Description. Morphometric data given in Table 2. Slender and large Odontostilbe species , largest male (holotype) 45.7 mm SL, largest female 47.7 mm SL. Body elongate and compressed, more compressed in males than females. Greatest body depth at dorsal-fin origin. Snout pointed in males, rounded in females. Head profile slightly convex from snout to dorsal-fin origin; profile descends from that point almost straight to caudal peduncle. Ventral profile convex from lower jaw to caudal peduncle. 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. Mouth terminal. Maxilla short terminates at vertical near or at anterior eye border, horizontal to lower eye border. Dentition (based on 6 c&s specimens and 28 alcohol specimens). Premaxillary teeth 4, 5, or 6, bearing 5-9 cusps (usually 7, 8, or 9); midcentral cusp longest, lateral cusps overlap cusps of adjacent teeth ( Fig. 15 ). Premaxillary teeth juxtaposed external to dentary teeth, leaving premaxillary tooth cusps exposed when mouth closed. Maxilla with 2 or 3 teeth bearing 1-9 (usually 7) cusps, decreasing cusp number toward posterior tip of maxilla. Dentary teeth 8-9 gradually decreasing in size posteriorly, anterior 6 teeth large bearing 5-7 cusps (usually 7), and posterior teeth small, conic or with 2-5 cusps. Smaller cusps of dentary teeth overlap cusps of adjacent teeth, usually not in posteriormost teeth.

Dorsal-fin rays ii (89), 9 (89). Dorsal fin slightly posterior to mid body length, and slightly posterior to pelvic-fin origin. First unbranched dorsal-fin ray in females and immature males about half length of second unbranched dorsal-fin ray. Second unbranched dorsal-fin ray elongate in mature males, extending beyond dorsal-fin distal profile. Anal-fin rays iii(1), iv(8), v (78), vi(2); 18(3), 19(15), 20(34), 21(31), or 22 (6). Analfin distal border concave, anterior 6-7 branched rays longest. Pectoral-fin rays i(89), 10(8), 11(55), or 12(26). Unbranched pectoral-fin ray reaching or not pelvic-fin origin, never extending beyond pelvic-fin origin. Pelvic-fin rays i (89), 6(1), 7(87), or 8(1). Unbranched pelvic-fin rays longest in mature males, extending beyond origin of anal fin. Lateral skin bor- der of unbranched pectoral-fin rays and unbranched pelvicfin rays thickened in mature males, bearing thin laterodorsal projection of hard tissue covered with soft tissue. Principal caudal-fin rays 19 (89). Procurrent caudal-fin rays: dorsal 8(1), 9(3), 10(5), 11(31), 12(44), or 13 (5); ventral 8(5), 9(33), 10(41), 11 (9), or 12(1). Sometimes 1-2 anterior ventral procurrent caudal-fin rays laterally expanded, bifurcated, or S-shaped. Caudal-fin ray flaps ventrally on 3 rd- 8 th rays of upper lobe, dorsally on 12 th- 16 th rays of lower lobe. Adipose-fin at vertical through to last anal-fin ray insertion.

Males with robust, elongate, retrorse hooks on posterior border of pelvic- and anal-fin rays. One to 3 paired or unpaired hooks per segment on last unbranched anal-fin ray, and 1 st to 16 th branched anal-fin rays, more developed from 1 st to usually 7 th rays and very small like knots usually on 10 th branched fin ray and following rays. Hooks on middle portion of anterior rays and on distal portion after 3 rd branched anal-fin ray. One to 3 unpaired acute, elongate hooks per segment of lepidotrichia along almost entire length of 1 st to 7 th branched pelvic-fin rays, and reaching tip of fin rays (except on 1 st branched pelvic-fin ray, on midlenght portion). No hooks found on 1 st unbranched pelvic-fin ray. One or two hooks on anterior border of branches of anal-fin rays. One or two hooks on anterior border of branches of pelvic-fin rays.

Scales cycloid; lateral line complete 35(6), 36(42), 37(11), or 38 (2); predorsal row 10(37), 11 (48), or 12(2); upper transverse rows 5(9), 6 (76), or 7(2); lower transverse rows 4 (87) or 5(1); scale rows around caudal peduncle 14 (73). Triangular modified scale on pelvic fin base extends posteriorly covering 2, 3 scales. Scales on anal-fin base 6 -8.

Cleared and stained specimens (5): supraneurals 4; precaudal vertebrae, 16(4) or 17(1); caudal vertebrae 18(1), 19(2), or 20(2); gill rakers, upper 5(2) or 6(3), lower 10(2) or 11(3) (2 on hypobranchial). Alcohol specimens (58): gill rakers, upper 5(35), 6 (22), or 7(1), lower 9(1), 10 (36), or 11 (21). Upper gill rakers with 1-6 recurved denticles on anterolateral border, and 1-3 similar denticles on posterolateral border; lower gill rakers with 1-6 recurved denticles on anterolateral border (1-4 anteriormost lower gill rakers with opposing 1-3 denticles); excepting posteriormost lower gill raker with 3-6 recurved denticles irregularly placed on anterior border, and 4-6 similar denticles on posterior border ( Fig. 16 a-d). Less numerous in small specimens (one specimen 27.1 mm SL, with none to 3 denticles on lateral border of upper gill rakers, and phores on unbranched pelvic-fin ray. Anal fin mostly clear with few dark chromatophores. Some specimens bearing dark chromatophores on distal portion of middle branched analfin rays. Adipose fin not pigmented. Caudal fin almost entirely covered with diffuse dark chromatophores along fin rays, except light areas on base of caudal-fin lobes just behind caudal-fin spot. Somewhat rounded brownish caudal spot on base of caudal fin, reaching upper border of peduncle, but never reaching lower border, sometimes extending on proximal portion of 7 th to 12 th central caudal-fin rays (specimens from río Cuyabeno). Holotype is not well-pigmented, with pelvic and anal fins hyaline.

Black chromatophores on snout, upper lip, sometimes on lower lip, anteriormost portion of maxilla, and 1 st, 2 nd, and 6 th infraorbitals. Pigmentation on top of head on frontals, and parietals with deep-lying dark chromatophores over brain membranes below frontals and parietals, and fontanel. Body with faint dark and silver midlateral stripe, sometimes reduced to one or two parallel lines, along middle longitudinal body axis, beginning above pseudotympanum, above lateral line, and reaching caudal spot. Guanine on eye iris, opercle, isthmus, and most of 3 rd, 4 th, and 5 th infraorbitals. Below lateral line, belly faint, chromatophores just above anal fin-base forming 6 to 10 chevron shaped markings.

none to 3 on lateral border of lower gill rakers). All denticulation mostly on basal portion of gill rakers.

Color in alcohol. General ground body color brownish yellow. Dark dorsum pigmentation from head to caudal peduncle, chromatophores mostly on border of scales. Pigmented scales extend laterally on body above longitudinal stripe, sometimes on pseudotympanum area in well-pigmented specimens. Dark chromatophores on all dorsal-fin rays, along 1 st and 2 nd unbranched fin rays and faint on 1 st- 8 th branched dorsal-fin rays, almost hyaline on 9 th branched ray. Dark chromatophores on 1 st unbranched pectoral-fin ray, less numerous on 1 st and 2 nd branched fin rays, following branched rays practically hyaline. Pelvic fins usually hyaline, with some dark chromato- Sexual dimorphism. Males with hooks on anal- and pelvicfin rays, elongate dorsal- and pelvic-fin rays, in contrast to absence of these features in females (see description). Gill gland (Burns & Weitzman, 1996) presents on first gill arch in mature males, covering about 8 to 12 anterior branchial filaments ( Fig. 16 ). Principal component analysis of morphometric data of males and females denotes sexual dimorphism in general body shape ( Fig. 17 ). Principal component 2 (PC2) grouped males and females separately, being affected strongly and negatively by snout length, pelvic-fin length, and caudal peduncle length; and positively by depth at dorsal-fin origin. Males are distinguished from females in all these characters, showing higher values of snout length, pelvic-fin length, and caudal peduncle length than females, while females have higher values of body depth at dorsal-fin origin than males ( Table 2). Principal component 3 (PC3) was affected strongly and positively by snout length and upper jaw length, and negatively by pelvic-fin length and dorsal-fin length. Some males have well-developed dorsal and pelvic-fin rays, and protuding snouts (greater snout length, and upper jaw length). This correlates with their heaviest loadings in PC3 forming a group on upper left corner of the graph ( Fig. 17 ).

Distribution. Río Napo, río Putumayo, and río Pastaza basins (a single lot known for the latter) ( Fig. 18 ). Nearly all material from Ecuador, and some lots from Peru on border with Ecuador. The species is also recorded on lower río Napo basin in sympatry with O. fugitiva .

Etymology. The epithet ecuadorensis refers to the country where the species was first discovered.

Ecological notes. Saul (1975) identified Odontostilbe cf. madeirae Fowler, 1913 , and Holoshesthes heterodon Eigenmann, 1915 as two cheirodontine species commonly taken together in the río Aguarico, the former primarily feeding on algae and plant material, and the latter on insects and insect larvae. However, examination of Saul’s (1975) material proved the species named O. cf. madeirae to be a mix of O. ecuadorensis described herein and O. euspilura . The material he named H. heterodon consist of an undescribed cheirodontine. Part of the specimens caugth by W. Saul was selected herein as type material for O. ecuadorensis . These Ecuadorian species are reported to occur in clearwater, blackwater or turbid waters, riverine sandy-beaches ( Stewart et al., 2002), or lagoons and associated tributaries ( Galacatos et al., 1996). All the material examined for this study came from altitudes between 200- 500 m. Galacatos et al. (1996) recognized two altitudinal regions in Ecuadorian Amazon, lowland between 200 m and 220 m, and piedmont between 235 m and 295 m, where most Odontostilbe species were caught, preferentially in lagoons rather than streams.

Figures

Fig. 14. Holotype of Odontostilbe ecuadorensis, ANSP 170608, male 45.7 mm SL (top), and paratypes MEPN 1517, 1 female 45.2 mm SL (middle) with exceptionally developed ovaries,ANSP 130574, female 46.6 mm SL (bottom).

Fig. 13. Upper and lower gill rakers counts of Odontostilbe fugitiva populations, and three new species Odontostilbe ecuadorensis, Odontostilbe nareuda, and Odontostilbe parecis.

Fig. 3. First gill arch of Odontostilbe fugitiva, MCP 35777, male 35.7 mm SL. SEM photographs of the first left side gill arch showing gill gland (top), in detail gill rakers on upper branchial branch (middle), and gill rakers on lower branchial branch (bottom). Lateral view.

Fig. 16. First gill arch of Odontostilbe ecuadorensis, FMNH 113514, male 40.6 mm SL (photos a, b, d). SEM photographs of the left side gill arch showing gill gland (a), in detail gill rakers on upper branchial branch (b), gill rakers on lower branchial branch (FMNH 113513, unsexed 32.5 mm SL) (c), and the posteriormost gill raker on the lower branch in detail (d). Lateral view.

Fig. 15. Dentition of Odontostilbe ecuadorensis, KU 13524, male 43.5 mmSL.SEM photograph ofleft side premaxilla (top), maxilla (middle), and dentary (bottom).

Fig. 17. Principal component analysis of the 18 morphometric data of males (M) and females (F) of Odontostilbe ecuadorensis. Stronger loadings on the second and third principal components (PC2, PC3).

Figs. 18. Distribution of Odontostilbe ecuadorensis (triangles), Odontostilbe nareuda (squares), and Odontostilbe parecis (losangles). Symbols can represent more than one lot, and more than one locality.