A new species of Moenkhausia Eigenmann ( Characiformes : Characidae ) from the upper rio Machado at Chapada dos Parecis , rio Madeira basin , Brazil

A new species of Moenkhausia is described from the upper rio Machado at Chapada dos Parecis, rio Madeira basin, Rondônia State, Brazil. Among congeners, the new species is similar to Moenkhausia chlorophthalma, M. cotinho, M. lineomaculata, M. plumbea, and M. petymbuaba by having dark blotches on the anterior portion of the body scales, which are absent in the remaining species of the genus. The new species differs from aforementioned species by possessing blue eyes in life, 15-18 branched anal-fin rays, and a well-defined, round caudal-peduncle spot that does not reach the upper and lower margins of the caudal peduncle and does not extend to the tip of the middle caudal-fin rays.


Introduction
The species of Moenkhausia Eigenmann, 1903 are widely distributed throughout the Neotropical Cis-Andean river basins, except for those in Patagonia, with greatest diversity occurring in the basins of the Amazon and Guianas (Lima et al., 2003).Moenkhausia is one of the most species-rich characid genera, currently comprising 80 valid species (Eschmeyer, 2015).Eigenmann (1903) proposed the genus based mainly on the combination of the presence of two rows of premaxillary teeth, five teeth on the inner row, completely pored lateral-line scales, a relatively straight lateral line, and small scales partially covering the caudalfin lobes.Lima et al. (2013) recorded twenty species of Moenkhausia in the rio Madeira basin, two of which were considered putatively new.During recent fieldwork in the upper rio Machado drainage, which is a major tributary of the rio Madeira in the state of Rondônia, an additional undescribed species was discovered and is herein described.The aim of the present contribution is to describe this new, beautifully-colored and apparently range-restricted species, and discuss its taxonomic placement among its congeners.

Material and Methods
Counts follow Fink & Weitzman (1974), except for the number of horizontal scale rows below lateral line, which is counted to the pelvic-fin insertion (excluding the axillary scale) rather than to the anal-fin origin.Measurements follow Fink & Weitzman (1974) with the addition of the distance from pelvic-fin origin to anal-fin origin.Standard length (SL) is expressed in millimeters (mm) and all other measurements are expressed as percentages of SL, except subunits of the head, which are expressed as percentages of head length.In the description, counts are followed by their absolute frequency in parentheses.Asterisks indicate the counts of the holotype.Scale circuli and radii were counted from the scale row immediately dorsal to the lateral line at the vertical through the dorsal-fin origin.Counts of supraneurals, branchiostegal rays, gill-rakers of the first branchial arch, tooth cusps, diminutive dentary teeth, unbranched anal-fin rays, procurrent caudal-fin rays, and the position of pterygiophores were taken from cleared and stained (c&s) specimens prepared according to Taylor & Van Dyke (1985).Vertebrae of the Weberian apparatus are counted as four elements and the compound caudal centrum (PU1+U1) as a single element.Precaudal vertebral counts include the Weberian apparatus and the vertebrae lacking haemal spines.Caudal vertebral counts include all vertebrae with haemal spines.Catalog numbers are followed by the total number of specimens and their SL range.The number of measured and counted specimens (if any) and the number of cleared and stained specimens (indicated by c&s) is given in parentheses, followed by their respective SL range.Institutional abbreviations follow Ferraris (2007) with the inclusion of UFRO-I (Universidade Federal de Rondônia, Porto Velho, Brazil).

Diagnosis.
Moenkhausia parecis is distinguished from all congeners, except M. clorophthalma Sousa, Netto-Ferreira & Birindelli, 2010, some populations of M. cotinho Eigenmann, 1908 (see Discussion), M. lineomaculata Dagosta, Marinho & Benine, 2015, M. petymbuaba Lima & Birindelli, 2009, and M. plumbea Sousa, Netto-Ferreira & Birindelli, 2010 by the presence of a dark blotch on the anterior portion of each scale of the second to seventh longitudinal series (vs.pigmentation absent or, when present, concentrated at the posterior margin of scales, forming a reticulate pattern).Moenkhausia parecis can be readily distinguished from all aforementioned species by having completely blue eyes in life (vs.green in M. clorophthalma, mostly green with some red in M. petymbuaba, lower portion blue and upper portion orange in M. lineomaculata, clear or red in M. cotinho, and clear, with a longitudinal dark stripe in M. plumbea).Additionally, it is distinguished from M. clorophthalma, M. petymbuaba and M. plumbea by having 15-18 (rarely 18) branched anal-fin rays (vs.18-24), from M. cotinho and M. lineomaculata by having a smaller caudal-peduncle spot, with only the base of the middle caudal-fin rays pigmented (vs.blotch larger, base of all caudal-fin rays pigmented in M. cotinho and M. lineomaculata, except the outermost unbranched rays in some specimens of M. lineomaculata) and by the absence of a light area preceding caudalpeduncle spot (vs.presence of a light area preceding caudal-peduncle spot).It can be further distinguished from M. clorophthalma, M. petymbuaba and M. plumbea by having a well-defined, round caudal-peduncle spot, that does not extend to the tip of the middle caudal-fin rays (vs.caudal-peduncle spot absent or poorly defined in M. clorophthalma and M. plumbea or caudal-peduncle spot confluent with longitudinal stripe on body, reaching the tip of middle caudal-fin rays in M. petymbuaba).
Description.Morphometric data of the holotype and paratypes presented in Table 1.Body compressed, moderately deep.Greatest body depth anterior to vertical through dorsal-fin origin.Dorsal profile of head convex from anterior tip of upper jaw to vertical through anterior nostril; straight or slightly concave from that point to tip of supraoccipital spine.Dorsal body profile convex from tip of supraoccipital spine to base of last dorsal-fin ray, approximately straight from that point to adipose-fin insertion and slightly concave along caudal peduncle.Ventral profile of body convex from anterior tip of dentary to anal-fin origin, straight along anal-fin base and slightly concave along caudal peduncle.
Mouth terminal, upper jaw slightly longer than lower jaw.Posterior terminus of maxilla reaching vertical through middle of pupil.Maxilla approximately at 45 degree angle relative to longitudinal axis of body.Nostrils close to each other, anterior opening circular, posterior opening crescent-shaped.Nostrils separated by narrow skin flap.
Longitudinal iridescent clear stripe at midline of body.Second to seventh dorsalmost scale rows with brown blotches on its anterior portion.Humeral blotch and caudalpeduncle spot conspicuous.All fins intense orange to yellow.

Sexual dimorphism.
No sexually dimorphic characters were found among analyzed specimens.
Etymology.The specific name parecis refers to the Chapada dos Parecis (plateau including the type locality), an important watershed that separates tributaries of three basins: rio Madeira, rio Tapajós and rio Paraguai.A noun in apposition.
Distribution.Moenkhausia parecis is known only from its type locality, a headwater tributary of igarapé Piracolina, itself a tributary of the upper rio Machado at Chapada dos Parecis, rio Madeira basin, about 9 km south of Vilhena, near the border of Rondônia and Mato Grosso States, Brazil (Fig. 3).Moenkhausia parecis is possibly an additional species endemic to the rivers draining the Chapada dos Parecis (see list in Ohara & Lima, 2015).
Ecological notes.The type locality of Moenkhausia parecis is located at 585 m above sea level on the Chapada dos Parecis.
It is a small "terra-firme igarapé" (= highland creek) with little preserved riparian vegetation and surrounded by large plantation fields (mostly soy and corn), near Vilhena, Mato Grosso.It is a clear water stream 1.5-2.5 m wide and 0.3-0.8m deep, with swift currents, and a bottom composed of sand and dead leaves (Fig. 4).2014), Moenkhausia parecis might be considered as 'Vulnerable (D2)', based on its occupation area (AOO) apparently less than 20 km 2 and the plausible future threat (agricultural development and expansion of Vilhena town around its very restricted distribution) that could lead the species to become critically endangered or extinct.

Discussion
The traditional classification system of the Characidae developed by Eigenmann (1917Eigenmann ( , 1918Eigenmann ( , 1921) ) delimited several genera based on morphological characters such as the form of the teeth, squamation of the caudal-fin, presence or absence of the adipose fin, and length of the lateral line.These characters were found subsequently to be highly homoplastic within the Characidae (Weitzman & Fink, 1983;Mirande, 2010;Marinho et al., 2014;Dagosta et al., 2014).As a consequence, Eigenmann's classification scheme resulted in the artificial delimitation of many groups of species.
One of the most remarkable features of Moenkhausia parecis is the presence of a dark blotch at the anterior portion of each scale of the second to seventh scale rows.This color pattern, which is relatively unusual within Characidae, is also present in Moenkhausia chlorophthalma, M. lineomaculata, M. plumbea, M. petymbuaba, and some populations of M. cotinho.Such feature was used by Sousa et al. (2010) to indicate a possible close relationship among the former three species.Based on body coloration and aspects of external morphology such as the relatively large head, the vertical orientation of the humeral blotch, the round dorsal-fin distal margin, and the relatively short anal-fin base, Moenkhausia parecis is similar to these species and may be closely related to them.However, such relationships are speculative and the monophyly of this group of species should be tested in a cladistic context.
A few other small characids possess similar body coloration to Moenkhausia parecis, such as A. maculisquamis Garutti & Britski, 1997, which is a member of the Astyanax bimaculatus (Linnaeus, 1758) complex.However, that species complex is defined by possession of a black, horizontally ovate humeral spot, and two diffuse vertical dark bars in the humeral region (Garutti & Britski, 1997;Garutti & Britski, 2000;Garutti & Langeani, 2009), neither of which occurs in Moenkhausia parecis.Therefore, there is no further evidence of a close relationship of the new species to members of this group.Two species of Jupiaba Zanata, J. kurua Birindelli, Zanata, Sousa & Netto-Ferreira, 2009 and J. meunieri (Géry, Planquette & Le Bail, 1996) possess dark blotches on the anterior portion of the body scales, as does Moenkhausia parecis.Birindelli et al. (2009) used that color pattern to indicate a close relationship between these species of Jupiaba.However, Moenkhausia parecis lacks the synapomorphic features of Jupiaba (Zanata, 1997;Zanata & Lima, 2005) including the presence of pelvic bone anteriorly developed as a spine, with its anterior portion free from musculature, and clearly does not belong to Jupiaba.
As mentioned, series of dark blotches on the body scales are also found in some populations of Moenkhausia cotinho, a widespread species of the Amazon, Orinoco and Essequibo basins.Members of Moenkhausia cotinho have a light area anterior to a large dark blotch on the caudal-fin base.These caudal marks, along with dark pigmentation concentrated on the distal border of the scales, forming a dark reticulate pattern, characterizes the "Moenkhausia oligolepis/M.sanctaefilomenae-species complex" (Costa, 1994;Lima & Toledo-Piza, 200;Lima et al., 2007).According to Lima & Toledo-Piza (2001) and Lima et al. (2007), M. cotinho is closely related to this group of species, despite not having the characteristic reticulate pattern on the majority of the body.Sousa et al. (2010), however, mentioned the presence of such reticulation on the scales below the lateral line in M. cotinho, and also noted the blotches on the anterior portion of the scales.

Table 1 .
Morphometric data of the holotype and paratypes of Moenkhausia parecis.Paratype range includes the values of the holotype.N = 30; S.D. = Standard Deviation.Dorsal portion of humeral blotch spanning three scales in width; ventral portion narrower, spanning just over one scale.Area posterior to humeral blotch followed by faint and wide horizontal dark stripe spanning two scale rows above lateral line that fades posteriorly on caudal peduncle; Color in alcohol.Overall ground color pale, with small dark chromatophores covering the entire head and body, densely concentrated on dorsal portion, gradually fading ventrally (Fig.1a).Dorsal midline of head and body dark brown.Jaws, opercular and infraorbital areas densely pigmented with small dark chromatophores.Opercular areas with guanine.Humeral blotch vertically oriented, extending two scale rows above and one or two scale rows below lateral line.
Despite intensive and broad collecting efforts in the rio Madeira basin during 2009 to 2013(Queiroz et al., 2013)and recent surveys conducted in the southeastern portion of Rondônia State and northwest of Mato Grosso State undertaken in 2010-2011 and 2013-2014, Moenkhausia parecis was only collected at its type locality.Additionally, examination of several fish collections failed to reveal additional specimens.Thus, it is possible that the species is restricted to the upper rio Machado, at the Chapada dos Parecis.The type locality of M. parecis is a small forest fragment near Vilhena town that is surrounded by farms.According to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, Tributary of igarapé Piracolina, upper rio Machado, Vilhena, Rondônia, Brazil, type locality of Moenkhausia parecis.Conservation status.