A new characid fish , Hyphessobrycon hexastichos ( Characiformes : Characidae ) from Chapada dos Parecis , Mato Grosso , Brazil

A new characid species, Hyphessobrycon hexastichos, is described from the upper rio Tapajós, Mato Grosso, Brazil. The new species is distinguished from all other Hyphessobrycon species by the presence of black zigzag longitudinal lines between longitudinal rows of scales in the lateral of body, maxilla with 3-5 teeth, i,6 pelvic-fin rays, 18-22 branched anal-fin rays, 4 scale rows above and 3 scale rows below of lateral line, lateral line with 9-13 perforated scales, and 33-35 scales in a longitudinal series.

The genus was proposed by Durbin in Eigenmann (1908) as a subgenus of Hemigrammus Gill, differing from the latter by the absence of scales on the caudal fin.Hyphessobrycon was extensively revised by Eigenmann (1918Eigenmann ( , 1921) ) whose accounts still constitute the single comprehensive review of the genus.The anatomical diversity within Hyphessobrycon, and the high number of species involved are the major reasons for the lack of phylogenetic analyses dealing with its inter-and intra-relationships.The recognition of groups of species is based primarily on similarities of color patterns and fin shape (Géry, 1961;Géry, 1966;Géry, 1977;Weitzman & Palmer, 1997).However, those authors only presented hypotheses of relationships for some of the possible species groups on Hyphessobrycon.
During a recent expedition to some of the south tributaries of the Amazon river in the Central and West regions of Brazil, a new characid species described below was collected in the upper rio Tapajós drainage.

Methods and materials
Counts and measurements were taken as described by Fink & Weitzman (1974) with the exception of the number of scale rows below lateral line that were counted from the scale row ventral of the lateral line to the scale row closest to the first pelvic-fin ray.Vertebral counts, supraneurals, gill-rakers of first arch, teeth and procurrent caudal-fin-ray counts were taken from cleared and stained specimens (c&s) prepared according to the method of Taylor & Van Dyke (1985).Teeth counts were also taken in all type specimens.Vertebral counts include the four vertebra of the Weberian apparatus, and the terminal centrum was counted as one vertebra.Lower and upper jaws of one c&s paratype prepared for SEM (scanning electronic microscopy).Measurements were taken point to point with an electronic caliper on the left side of specimens when possible.

O F S
Hyphessobrycon hexastichos, new species Moenkhausia agnesae, non Géry, 1965. -Notare (1994:6-7; misidentification; photo of live specimen).Premaxilla with two tooth rows; outer row with 3-4, rarely 2, pentacuspid teeth with central cusp larger; inner row teeth 5, rarely 6, gradually decreasing in length from first to fourth teeth, last tooth considerably smaller, with 5-9 cusps and central cusp longer and broader than other cusps.Three to 5 maxillary teeth, with 5-7 cusps, central cusp slightly longer.Four or 5 anterior-most dentary teeth larger, with 7 cusps, followed by 1-2 middle sized tooth with 5-7 cusps, and 6-7 teeth with 1-3 cusps or conical in shape; central cusp in all teeth two to three times longer and broader than remaining cusps.Cusp tips slightly curved posteriorly and towards inside of mouth (Fig. 2).
Dorsal-fin rays ii, 9 (n = 20), first unbranched ray approximately half length of second ray.Dorsal-fin origin located anterior to middle of SL and posterior to vertical through pelvic-fin origin.Fleshy flaps on anterior 5 dorsal-fin rays, attached to fin ray and extended over membrane between rays.Adipose-fin located approximately at vertical through insertion of 16th to 19th anal-fin rays bases.
Scale sheath along anal-fin base with 7-11 scales in single series, extending posteriorly to base of fifth to ninth branched rays.
Color in alcohol.Dorsal and dorsolateral portions of head and body dark brown.Portion midventral of body above anal fin with red-orange chromatophores in large specimens (38.3 mm SL).Infraorbital and opercular areas covered with scattered, dark chromatophores.Scales on lateral and ventral surface of body with dark brown chromatophores.Black zigzag longitudinal stripes between longitudinal body rows of scales in lateral of body.Specimens larger than 38.1 mm SL with five to six conspicuous longitudinal black stripes, two midlateral longitudinal black stripes densely pigmented above perforated scale series, one faint zigzag above these stripes, and three zigzag longitudinal stripes below perforated scale series.Specimens smaller than 38 mm SL with three or four dark stripes in midlateral body.One black humeral spot, narrow and vertically elongate, upper portion wider, located over first to third lateral line scales and extending over 2-3 horizontal series of scales, including lateral line.Silvery to violet midlateral body stripe extending from humeral region to caudal peduncle, between two longitudinal stripes above perforated scales.Caudal-fin median rays pigmented forming stripe.Small black chromatophores scattered over rays of all fins.Anal fin with small black chromatophores along its distal margin forming narrow stripe in some specimens (Fig. 1).
Color just after fixation.Color pattern similar to described for alcohol preserved specimens, except as follows.Some specimens examined soon after fixation in formalin, with all fins reddish.Lateral surface of body silvery.Body red-orange.
Sexual dimorphism.Secondary characters were not found on examined specimens.Mature gonads were not found on the four dissected cleared and stained specimens (MCP 37649, 32.0-38.8mm SL).
Etymology.The specific epithet hexastichos is from the Greek, hexas, six, and stichos, meaning line or row, referring the presence of six conspicuous black zigzag longitudinal stripes between longitudinal body rows of scales in large specimens.

Ecological notes.
All specimens of H. hexastichos were collected along the margin in semilentic stretches of a shallow river with clear water, with sand and scattered small stones on the bottom, and a small amount of riparian vegetation.Species collected syntopically with H. hexastichos were Aequidens Table 1.Morphometric data of holotype (H) and paratypes of Hyphessobrycon hexastichos (MCP 37648,1;MCP 37649,14 of 145;MZUSP 87242,5 of 20).SD = standard deviation.

Discussion
The new species is described in Hyphessobrycon according with the definition proposed by Durbin in Eigenmann (1908) and further elaborated by Eigenmann (1918): premaxillary teeth in two rows; maxillary teeth absent or reduced in number and restricted to the upper portion of its free margin; lateral line incomplete; adipose fin present, and caudal fin not covered with scales.
Weitzman & Malabarba (1998) and Lucena (2003) pointed that there is no evidence that Hyphessobrycon is monophyletic, and recognition of monophyletic groups among Hyphessobrycon species is complicated by the difficulty in finding characters useful for hypothesis of relationships among the species.Weitzman & Malabarba (1998) indicated that large characid genera such as Hyphessobrycon often have minimal morphological divergence useful for cladistic analyses of their species.Much of the information used to distinguish species are probably labile features such as variation in color pattern, counts and body proportions, that are little informative about phylogenetic relationships.Géry (1977: 458-459), proposed six artificial groups to the Hyphessobrycon species based on color pattern, H. hexastichos color pattern doesn't fit any of his group proposed.
The number of pelvic-fin rays in most Hyphessobrycon species usually is i,7; but all specimens examined of H. hexastichos have only i,6; an uncommon count also to most genera of the Characidae.Hyphessobrycon hexastichos possess only three scale rows between lateral line and pelvic-fin origin, while most Hyphessobrycon species have four to six scale rows.Five Hyphessobrycon species were previously described from the rio Tapajós drainage: H. pulchripinnis Ahl, 1937, H. cachimbensis Travassos, 1964, H. vilmae Géry, 1966, H. heliacus Moreira, Landim & Costa, 2002, and H. scutulatus Lucena, 2003, the three last species from upper rio Tapajós drainage.None of these species possess black zigzag longitudinal stripes between longitudinal body rows of scales in the lateral of body as present in H. hexastichos.
The ichthyofauna of the rio Tapajós drainage is poorly known.Reports on the species composition of the drainage are nonexistent.During the collecting expedition to several affluents of rio Tapajós, rio Madeira, rio Purus and rio Paraguay drainages, H. hexastichos was collected only in the rio Mutum, tributary of the upper rio Tapajós, as also verified by Notare (1994).
at dorsal-fin base; straight from last dorsal-fin ray to adiposefin origin.Ventral profile of head convex.Ventral body profile convex from pectoral-fin origin to anal-fin origin.Body profile along anal-fin base posterodorsally inclined.Caudal peduncle profile nearly straight to slightly concave along both dorsal and ventral margins.Snout convex from margin of upper lip to vertical through anterior nostrils.Head small.Mouth terminal.Maxilla extending posteriorly to vertical through middle of orbit, slightly curved, forming angle of 45 o with longitudinal axis of body.Anterodorsal border of maxilla concave, posterodorsal border slightly convex, anteroventral border concave, and posteroventral border convex.Maxilla slightly widened posteriorly.