Odontostilbe parecis, 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 : 188-193

Odontostilbe parecis , new species

Fig. 24

Holotype. INPA 24885 , 1 (male 33.0 mm SL), Brazil, Mato Grosso, BR 174 , Corredeira Papagaio, [near BR 364 , rio Galera, upper rio Guaporé basin], Equipe Rose, V. Py-Daniel et al., 3 Oct 1984.

Paratypes. BRAZIL, MATO GROSSO: INPA 21424 , 4 m of 8 (1 male 35.0 mm SL, 3 unsexed 29.8-36.2 mm SL), same data as holotype . INPA 21425 , 1 m of 23 (male 30.6 mm SL), rio Novo , BR 174 , [near BR 364 , rio Novo, rio Galera, upper rio Guaporé basin], Equipe Rose , V. Py-Daniel et al., 2 Oct 1984 . MCP 37318, 129 (unsexed 16.7-38.0 mm SL), Nova Lacerda, rio Galera, affluent of rio Guaporé in Balneário Galera , V. Bertaco et al., 14°28’59’’S 59°35’07’’W, 12 Jul 2004 . MCP 37319, 14 m of 82 (5 males 30.3- 39.0 mm SL, 1 male 32.8 mm SL c&s, 4 females 33.6-41.6 mm SL, 1 female 36.8 mm SL c&s, 3 unsexed 31.3-34.4 mm SL), Pontes e Lacerda, affluent of rio Galera about 71 km north of rio Guaporé , 14°39’12’’S 59°26’46’’W , R. Reis et al., 12 Jul 2004 .

Non-type material. Rio Madeira - Rio Guaporé basin, BRASIL, MATO GROSSO: MCP 38493, 45 (2 males 31.8-32.3 mm SL, 43 unsexed 15.6-38.7 mm SL), Comodoro, stream affluent of rio Novo on the road BR 174 , 14°13’25’’S 59°41’27’’W .

Diagnosis. Differs from Amazonian species of Odontostilbe by: (1) number of lower gill rakers 9-10 (vs. 11-14 in Odontostilbe fugitiva and O. dierythrura , 10-11 in O. ecuadorensis , and 10-12 in O. nareuda ) ( Fig. 13 a-b); (2) number of branched anal-fin rays (20-21, vs. 23-26 in O. nareuda ); (3) terminal mouth (vs. conspicuous subterminal mouth in O. euspilura ); (4) longer upper jaw length 28.8-32.9% HL (vs. 23.4-30.0% HL in O. fugitiva , Fig. 25 , or vs. 23.0-29.2% HL in O. ecuadorensis ); and (5) larger eye in males 38.9-40.8% HL diameter (vs. 28.9-38.6% HL in O. fugitiva , Fig. 26 , or vs. 33.3- 38.1% HL in O. ecuadorensis ). The combination of the characters listed above distinguishes O. parecis from all other Odontostilbe species.

Description. Morphometric data given in Table 4. Largest male reaching 35.0 mm SL, and female 41.6 mm SL. Body elongate and compressed. Males with more elongate and compressed bodies than females. Greatest body depth at dorsalfin origin. Snout blunt, larger in males. Head profile pointed, gently convex from snout to posterior tip of supraoccipital bone. Dorsal profile ascends almost straight from that point to dorsal-fin origin, sometimes with sligth depression at posterior tip of supraoccipital; from dorsal-fin origin descends almost straight to caudal peduncle. Ventral profile convex from lower jaw to anal-fin origin, and straight along anal-fin base. 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, terminating posteriorly at vertical near anterior eye border, and ending at level equal to inferior eye border, positioned at 45 degrees angle relative to longitudinal body axis. Cleared and stained specimens (2). Premaxillary teeth 5, bearing 8-10 cusps; midcentral cusp longer than lateral cusps; smaller lateral cusps of each tooth overlap cusps of adjacent teeth ( Fig. 27 ). Premaxillary teeth juxtaposed externally to dentary teeth, leaving premaxillary tooth cusps exposed when mouth closed. Maxilla with 2-3 teeth bearing 7-9 cusps, usually decreasing cusp number to posterior tip of maxilla. Dentary teeth 8-9 bearing 2-7 cusps, gradually decreasing in size posteriorly, first 6-7 teeth large with 6-7 cusps, following 2 small teeth with 2-5 cusps. Smaller cusps of all dentary teeth overlaping adjacent teeth cusps, usually not in posteriormost teeth. All dentary tooth cusps slightly recurved towards interior of mouth.

Dorsal-fin rays ii (20) or 9 (20). Dorsal-fin origin slightly posterior to midlength of body, and slightly posterior to vertical through pelvic-fin origin.Anal-fin rays v (20), 19(5), 20(8), or 21 (7). Anal-fin distal border concave, anterior 6-7 branched rays longest. Pectoral-fin rays: i (20), 9(1), 10(7), 11 (10), or 12(2). Unbranched pectoral-fin ray short of reaching or reaching pelvic-fin origin, slightly extending beyond pelvic-fin origin in males. Pelvic-fin rays i(20), 6(1), or 7 (19). Unbranched dorsal or pelvic-fin rays not elongate in males. Lateral skin border of unbranched pectoral-fin rays and unbranched pelvic-fin rays thickened in mature males, bearing thin laterodorsal projection of hard tissue covered with soft tissue. Principal caudal-fin rays 19 (20). Procurrent caudal-fin rays: dorsal 10(2), 11 (9), or 12(9); ventral 8(3), 9 (15), or 10(2). Anterior ventral procurrent caudal-fin rays distally bifurcated or not. Caudal-fin ray flaps ventrally on 2 nd -8 th (mostly 4 th- 7 th) rays of upper lobe, and dorsally on 12 th- 16 th (mostly 13 th- 15 th) rays of lower lobe. Adipose fin at vertical through last analfin ray insertion.

Males with acute, retrorse hooks on posterior margin of pelvic and anal-fin rays. One or two paired and unpaired hooks per segment of lepidotrichia, on last unbranched anal-fin ray, and 1 st to 8 th branched anal-fin rays, positioned at middistal length of rays and usually not extending to ray tip; tiny hooks can be present up to 16 th anal-fin branched ray, occurring distally on branches (up to 17 th anal-fin branched ray in holotype). One or two unpaired hooks per segment of lepidotrichia on 1 st to 7 th branched pelvic-fin rays, extending almost entirely to distal ray tip (along midlenght of 1 st branched pelvicfin ray). Few mature males available for description of hooks. Type material from INPA contains males with more developed hooks. Holotype with hooks on 2 nd to 5 th branched pelvic-fin rays. Because available males are not fully mature, this species could have typical elongation of unbranched dorsal and pelvic-fin rays present in of Odontostilbe species.

Scales cycloid; lateral line complete 35(7) or 37(1); predorsal row 9(2), 10 (12), or 11(3); scale rows between lateral line and dorsal-fin origin 5 (10) or 6(8); scale rows between lateral line and anal-fin origin 4 (18); scale rows around caudal peduncle 14(10). Triangular modified scale on pelvic fin base extends posteriorly covering 1-2 scales (mostly 2). Scales on anal-fin base 5-7 (partially missing in holotype).

Cleared and stained specimens (2): supraneurals 4(2); precaudal vertebrae, 15(1) or 16(1); caudal vertebrae 19(2). Gill rakers (18 in alcohol, 2 c&s), upper 5 (17) or 6(3), lower 9(12) or 10 (8) (2 on hypobranchial). Upper gill rakers with none or 1-3 recurved denticles along anterolateral border, and none to 2 similar denticles on posterolateral border; lower gill rakers with none to 5 recurved denticles on anterolateral bor- der (1-4 anteriormost lower gill rakers with none to 2 denticles on posterolateral border); excepting posteriormost lower gill raker with 4 recurved denticles irregularly placed on lateral surface ( Fig. 28 ). All denticulation mostly on basal portion of gill rakers.

Color in alcohol. General ground body color brownish or pale yellow. Dorsum dark from head to caudal peduncle, chromatophores mostly on scale borders forming reticulated pattern. Pigmented scales extend laterally on body below longitudinal stripe, also on pseudotympanum area. Dorsal fin with scattered chromatophores along all fin rays, more densely pigmented along 1 st and 2 nd unbranched dorsal-fin rays. Pectoral and pelvic fins with scattered dark chromatophores, more numerous on anteriormost portions of fins. Holotype with pelvic fin hyaline. Anal fin mostly pigmented with chromatophores spread on all fin rays, except at distal tips of last unbranched fin ray and 1st branched fin ray. Adipose fin hyaline. Caudal fin almost entirely covered with diffuse chromatophores along fin rays, clear areas on base of caudal-fin lobes just posterior to caudal-fin spot. Rounded black to brown spot on base of caudal fin, usually light near lower border, sometimes extending little onto proximal portion of 7 th to 12 th central caudal-fin rays.

Numerous chromatophores on snout, upper and lower lips, anteriormost portion of maxilla and lower jaw, and 1 st- 2 nd infraorbitals. Pigmentation on dorsal surface of head on frontals and parietals, and deep-lying dark chromatophores over brain membranes below frontals and parietals, and fontanel. Body with faint dark midlateral stripe, sometimes reduced to line, along midlongitudinal body axis, beginning posterior to or on pseudotympanum, above lateral line, reaching caudal spot. Below lateral line, ventral body faint almost without chromatophores. Pigmented area above anal-fin base forming 10 to 11 chevron-shaped markings. Guanine surrounds eye iris, interopercle, opercle, ishtmus, and most 3 rd infraorbital. Holotype with some remaining guanine, but fresher specimens of MCP without any guanine.

Sexual dimorphism. Males with anal- and pelvic-fin hooks on rays as previously described, such hooks absent in females. Gill gland (Burns & Weitzman, 1996) present in three mature males of Odontostilbe parecis , holotype, and two paratypes ( Fig. 28 ). Holotype of O. parecis with gill gland present on first gill arch, covering about 9 anterior branchial filaments. Paratype INPA 21425, a male 30.6 mm SL with a gland including about 7 anterior branchial filaments and paratype MCP 37319, 39.0 mm SL with gland including about 6 anterior branchial filaments. Principal component analysis of morphometric data of males and females plus unsexed specimens shows sexual dimorphism in general body shape ( Fig. 29 ). Principal component 2 (PC2) grouped males and females separately. This affected strongly and negatively by caudal peduncle length, pectoral-fin length, pelvic-fin length, and snout length; and positively by depth at dorsal-fin origin. Principal component 3 (PC3) affected strongly and positively by snout length and caudal peduncle length, negatively by anal-fin base and pectoral-fin length. Males differed from females in all of these characters. Usually males with higher mean values for peduncle length, pectoral-fin length, pelvic-fin length, and snout length, while females and unsexed specimens have higher depth at dorsal-fin origin than males ( Table 3). Unsexed specimens were not assumed to be females, because they probably also include immature males. All examined males are probably not fully mature as mentioned in description.Additional material may reinforce sexual morphometric characters described here.

Distribution. Upper rio Guaporé drainage, rio Galera and rio Novo.

Etymology. The epithet parecis refers to the Chapada dos Parecis, a plateau situated on the east of Guaporé tributaries where the species was discovered.

Ecological notes. The Guaporé-Iténez is a clearwater rightbank tributary of the major rio Madeira ( Goulding et al., 2003). Field notes record of MCP material: translucent water of quiet to medium flow, sandy bottom with pebbles, and a depth of 1- 1.2 m. This was species collected along with Serrapinnus sp.

Figures

Fig. 24. Holotype of Odontostilbe parecis, INPA 24885, male 33.0 mm SL (top), and paratypes MCP 37319, male 33.0 mm SL (middle), female 41.6 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. 25. Upper jaw lenght as a function of head length for males, females, and unsexed specimens of Odontostilbe fugitiva and Odontostilbe parecis.

Fig. 26. Eye diameter as a function of head length for males of Odontostilbe fugitiva and Odontostilbe parecis.

Fig. 27. Dentition of Odontostilbe parecis, MCP 37319, male 32.8 mm SL. SEM photograph of left side premaxilla (top), maxilla (middle), and dentary (bottom).

Fig. 28. First gill arch of Odontostilbe parecis, INPA 21425, male 30.6 mm SL. SEM photographs of the left side gill arch (top), in detail gill rakers on upper branchial branch (middle), and gill raker on lower branchial branch (bottom). Lateral view.

Fig. 29. Principal component analysis of the 18 morphometric data of males (M), females (F), and unsexed specimens (U) of Odontostilbe parecis. Stronger loadings on the second and third principal components (PC2, PC3).