Ver tebrate Zoology New and poorly known Characiform fishes ( Teleostei : Characiformes : Characidae ) from French Guyana . A new Tetra of the genus Bryconamericus

Bryconamericus guyanensis sp. n. is described from French Guyana. The new species is closely related to B. subtilisform ROMAN-VALENCIA, 2003 and characterized by the following features: (1) body depth relatively low (3.49 – 4.16), (2) anal-fi n with 19 – 21 branched rays, (3) 17 – 21 setiform gill-rakers, (4) 38 – 41 scales in a longitudinal row, (5) 41⁄2 – 5/1/3 transversal scales, (6) 37 to 40 vertebrae (total), (7) two to three trito quincuspid maxillary teeth, and (8) premaxilla in the outer row with four to fi ve (mostly fi ve) trito quincuspid teeth which are implanted in an irregularly row.


Introduction
French Guyana has a very important biodiversity, particularly pronounced among freshwater fi sh.Endemic species are frequent, over forty of them are new and still to describe.This article aims to complement the knowledge on Characidae of French Guyana (see also GÉRY et al., 1996;GÉRY et al., 1988;GÉRY et al., 1995;GÉRY et al., 1998;JÉGU et al., 2002;JÉGU et al., 2003;ZARSKE et al., 2004;ZARSKE et al., 2005) and to enable managers of natural environments to better protect them.The publication of this paper was delayed because of the death of one of the authors.This paper describes a new species of Bryconamericus, which was mentioned in some previous publications under the name B. spec.aff.stramineus (GÉRY & PLANQUETTE, 1983;GÉRY et al., 1991;PLANQUETTE et al., 1996;BOU-JARD et al., 1997).

Materials and methods
Measurements were taken, with an accuracy of 0.1 mm, on the left side of each specimen with digital callipers under a binocular microscope.All counts and measurements were recorded following GÉRY (1972).The number of supraneurals, vertebrae and pterygiophores were counted by x-ray investigation (Faxitron 43855C).The count of vertebrae includes all vertebrae, considering the urostyle as the last one.Precaudal and caudal vertebrae are distinguished by the presence or absence of haemal spines.The four vertebrae of the Weberian apparatus, the precaudal and caudal vertebrae are separated by a plus sign.
The holotype and some paratypes of the described species are deposited in the Galerie d'Ichtyologie du Museum national d'Historie naturelle, Paris, France (MNHN); some paratypes are deposited in the following collections:
Description (n = 10 from lot 3; 37.8 -46.8 mm SL; fi rst fi gure = holotype; second fi gure = mean; fi gures Vertebrate Zoology ■ 60 (1) 2010   between the brackets = Variability).The variability of morphometric (expressed in percent of standard length or head length) and meristic features see Table 1 and 2 The dorsal-fi n originates distinctly anterior to the middle of the body.The predorsal area is 2.07; 2.06 (2.00 to 2.12) times in SL.The basis of dorsal-fi n is 2.04; 1.92 (1.68 to 2.20) times in head length.The third fi n ray is the largest and the fi rst branched one.It is smaller than head and 1.17; 1.19 (1.03 to 1.36)  times in head length.Fin rays: ii 8. 9 pterygiophores of the dorsal-fi n (counted in x-ray investigation).The dorsal-fi n starts with the fi rst pterygiophore between the seventh and eighth precaudal vertebrae.
Anal-fi n relatively long, somewhat larger than the head, beginning below the last fi n rays of the dorsalfi n.The fi rst fi n rays are a little longer.There is a weakly concave lappet at the beginning of the fi n.The preanal area is 1.78; 1.73 (1.64 to 1.81) times in SL.The anal-fi n base is 0.76; 0.81 (0.73 to 0.92) times in head length.Anal-fi n with a basal sheath of a single series of 10 to 19 scales which reach up to about the 12 th or 18 th branched fi n ray.The fi fth or sixth fi n ray is the largest and the fi rst branched one, 1.95; 1.59 (1.45 to 1.95) times in head length.Fin rays: iv to v 19 to 21 (i) (n = 22), mean 20.1.Anal-fi n with 21.7 (20 to 23) pterygiophores (n = 22, counted in x-ray investigation).The anal-fi n starts with one to two pterygiophores between the fi rst and second or second or third and forth caudal vertebrae.No hooklets on the fi rst rays of anal-fi n.
The ventral-fi ns are situated anterior to the dorsal-fi n.The preventral area is 2.29; 2.23 (2.14 to 2.33) times in SL.The length of ventral-fi n is 2.15; 1.93 (1.55 to 2.15) Scales in a longitudinal row 39.3 (38 to 41, n = 10), 8½ -9 (4½ -5/1/3) transversal scales anterior to dorsal fi n.Lateral line complete.11 to 13 predorsal scales in a regularly row.12 -13 scales around caudal peduncle.No scales on the basis of caudal-fi n. 18.6 (17 to 21) relatively short, setiform gill-rakers on the fi rst arch of the left side, six to seven on the upper and ten to fourteen on the lower branch.

Coloration (in vivo)
. Body pale to medium yellow, belly silvery, somewhat darker dorsally.Scales of dorsal part of body with a dark brown to black margin.A dark yellow to silvery lateral band extends from the gill cover to the base of caudal-fi n.A black vertically prolonged humeral spot.The black caudal spot is prolonged to of middle caudal fi n rays, sometimes reaching the tips.Iris of the eye silvery to light yellow, upper part reddish.Fins hyaline with white margins, some yellow and black melanophores on the basal parts of dorsal-fi n and of the lobes of caudal-fi n, also in the middle of anal-fi n (see also Figs. 3 and 4).

Coloration (in alcohol)
. Body pale to medium brown, belly lighter, somewhat darker dorsally.There is the same pattern as in living specimens: a vertically prolonged humeral spot, a light longitudinal band from the gill cover to the caudal peduncle ending in a deep brown or black caudal spot prolonged to the middle caudal-fi n rays.No further markings on the fi ns (see also Fig. 1).

Distribution.
The species was collected in all river basins of French Guyana (see also PLANQUETTE et al., 1996, page 241).
Habitat and ecology.This species is present in the upstream part of the fi rst rapids of various rivers.Catches are often abundant which suggests gregarious behavior.B. guyanensis sp.n. frequents shallow (10 -50 cm) tributaries where the water is clear, the current relatively fast (0.5 -1 m/s), and the substrate composed primarily of rock, gravel and sand, sometimes with mud and plant debris.It is accompanied by different species of Characidae (Hemibrycon surinamensis, Moenkhausia moisae, M. oligolepis), Lebiasinidae (Pyrrhulina fi lamentosa), Callichthyidae (Corydoras guianensis) and Cichlidae (Crenicichla albopunctata, Krobia itanyi).We can also meet B. guyanensis sp.n. in areas of rapid.During the month of October, the more squat specimens are adult females ready to spawn.
The genus Bryconamericus EIGENMANN, 1907 (type-species: B. exodon EIGENMANN, 1907) is characterized by the following combination of characters: (1) two rows of teeth on the premaxilla with four teeth in the inner series, (2) a low number of teeth along the anterior margin of the maxilla, (3) lack of scales on the caudal fi n, (4) a large third suborbital (= infraorbital) contacting the preopercle along its posterior and ventral margins, ( 5) setiform gill-rakers, (6) a complete laterosensory canal system on the body, and ( 7) the absence of a glandular pouch on the base of caudal fi n in males (DA SILVA, 2004).There are some groups of species in the genus which differentiate by the arrangement of teeth in the outer row of premaxillary bone.
The differentiation of the genus Knodus EIGEN-MANN, 1911 (type-species: Bryconamericus breviceps EIGENMANN, 1908) is discussed.The main difference between Bryconamericus and Knodus is the scalation of the base of the caudal-fi n (Knodus: base of caudalfi n scaled and Bryconamericus: base of caudal-fi n not scaled).There are authors which accept Knodus as a valid genus (e.g.GÉRY, 1978;LIMA et al., 2004;ZAR-SKE & GÉRY, 2006;FERREIRA & LIMA, 2006;FERREIRA & CARVAJAL, 2007;ZARSKE, 2007ZARSKE, , 2008;;VARI et al., 2009, and others) and authors which do not accept Knodus (THAPHORN, 1992;ROMAN-VALENCIA, 2003, 2005).Here we accept Knodus because the phylogenetic relationships of the whole old Tetragonopterinae is not solved and if we do not accept the differentiation between Bryconamericus and Knodus so we also can not accept for example the differentiation between Astyanax and Moenkhausia or Hyphessobrycon and Hemigrammus.We think that it is better up to a general solution of the relationships to use the old view of the problem.K. heteresthes (EIGENMANN, 1908) is only known member of the genus Knodus from the Guyana Shield.The main differences between these species and B. guyanensis sp.n. are the following: The most discriminant character is the number of rays in anal-fi n.  (4.25 -4.5 vs. 3.49 -4.16) (BRITSKI et al., 1999).
. Body elongated and slender, laterally compressed, broadest behind the head.The dorsal outline rises in a regular curve up to the anterior root of the dorsal-fi n and is equal or less curved than the ventral outline.Preventral area fl at, especially anterior to the beginning of ventral-fi n.Greatest body depth approximately anterior to the beginning of ventral-fi n, Depth at the beginning of dorsal-fi n3.75; 3.73 (3.49 to 4.16) times in standard length (SL).The males are somewhat more slender than the females.The head is relatively small.The head length is4.61; 4.41  (4.05 to 4.81) times in SL.Eye relatively large.The eye diameter is 2.64; 2.65 (2.19 to 3.11) times in head length.Interorbital width slightly arched, 4.27; 3.79 (3.38 to 4.32) times in head length.Mouth terminal, sometimes directed slightly upwards, not pointed, nearly rounded, relatively short, snout 4.27; 3.79 (3.38 to 4.32) times in head length.Mandibulary bone not or only slightly prominent.Maxilla relatively short and broad, up to the rim of the pupil, 4.46; 4.13 (3.58 to 4.71) times in head length.Third suborbital is complete and large contacting the preopercle along its posterior and ventral margins.Fontanels are relatively large and long, craniad up to the eyes.The caudal peduncle is longer than high.The height of caudal peduncle is 1.87; 1.70 (1.58 to 1.92) times in its length.Interorbital width fl at or little curved, 2.89; 2.99 (2.81 -3.60) in head length.Premaxillary teeth arranged in two rows.The teeth of external row are irregularly implanted.Four to fi ve (mostly fi ve) tri-to quincuspid teeth are situated in the outer row and four quincuspid teeth in the inner row.The teeth are narrow at their bases, compressed.The lateral cusps begin relatively low.The cusps of the teeth of the inner row are arranged in a semicircle.Maxilla with two to three tri-or quincuspid teeth.Dentary bone with four large, quincuspid teeth followed by some abruptly smaller conical teeth.

Table 1 .
Morphometric variability of Bryconamericus guyanensis sp.n. from different localities in French Guyana (all lots n=10).

Table 2 .
Meristic variability of Bryconamericus guyanensis sp.n. from different localities of French Guyana.