Chrysobrycon yoliae , a new species of stevardiin ( Characiformes : Characidae ) from the Ucayali basin , Peru

Chrysobrycon yoliae, new species, is described from a drainage flowing into the río Yucamia basin, río Ucayali basin, Peru. Chrysobrycon yoliae is readily distinguished from its congeners by the anterior tip of pelvic bone situated anterior to the fifth rib (vs. situated posterior to the fifth rib), the presence of 20-26 dentary teeth (vs. 11-19), and the possession of a terminal lateral-line tube between caudal-fin rays 10 and 11 (vs. the absence of this tube, except in C. eliasi). The new species differs from C. eliasi and C. myersi by the presence of teeth on third pharyngobranchial (vs. the absence of teeth on this bone) and also differs from C. eliasi by the dorsal-fin origin situated at vertical through anal-fin rays 5 to 7 (vs. located at vertical through anal-fin rays 8 to 10), the posterior extent of the ventral process of quadrate reaching the vertical through posterior margin of symplectic (vs. not reaching the vertical through posterior margin of symplectic), the dorsal-fin to adipose-fin length 26.8-28.8% SL (vs. 23.9-26.8% SL), and the body depth at dorsal-fin origin 34.4-42.2% SL (vs. 24.1-34.5% SL). A key for the identification of Chrysobrycon species is provided.


Introduction
Chrysobrycon Weitzman & Menezes is diagnosed by a characteristic pouch scale on the ventral lobe of the caudal fin in mature males (Weitzman & Menezes, 1998).This pouch scale is relatively small, somewhat elongated, curved, and horizontally folded so that its lateral face forms a laterally concave, broadly open pocket (Weitzman & Menezes, 1998).In fact, this type of pouch scale is unique within the Xenurobryconini (Weitzman & Fink, 1985), a tribe in which Weitzman & Menezes (1998) classified the genus.
New Chrysobrycon from western Amazon 292 Chrysobrycon species are strictly cis-Andean occurring in freshwater ecosystems between 153 and 585 m above sea level (a.s.l.) in the upper Amazon basin in Colombia, Ecuador, and Peru (Böhlke, 1958;Weitzman & Thomerson, 1970;Vanegas-Ríos et al., 2011;Vanegas-Ríos et al., 2013b).According to Weitzman & Thomerson (1970), Vanegas-Ríos et al. (2011), andVanegas-Ríos et al. (2013b), C. myersi is the only species that occurs in the río Ucayali basin.Chrysobrycon myersi is easily distinguished within the genus not only by its secondary sexually dimorphic characters in males (e.g., spinelets on pelvic-, anal-, and caudal-fin rays), but also by meristic and morphometric differences (Weitzman & Thomerson, 1970;Vanegas-Ríos et al., 2011).We examined several specimens from an unnamed drainage flowing into the río Yucamia system (río Ucayali basin) that did not correspond to the described species of Chrysobrycon.Therefore, we describe these specimens as a new species of Chrysobrycon and provide a key to identify the species of the genus.

Material and Methods
The studied specimens are deposited in the collections of Asociación Ictiológica, La Plata (AI); Academy of Natural Sciences of Drexel University, Philadelphia (ANSP), Fundación Miguel Lillo, Tucumán (CI-FML); Natural History Museum of Los Angeles County, Los Angeles (LACM); Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, Lima (MUSM); Museo de La Plata, La Plata (MLP); and National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM).Counts of the pectoral-, pelvic-and dorsal-fin rays are presented according to Böhlke (1958).Measurements and other counts follow Fink & Weitzman (1974) and Menezes & Weitzman (2009), with the addition of measurements described by Vanegas-Ríos et al. (2013a).The gill-gland length was measured in males from its anterior to its posterior margins of fused gill filaments.Measurements were taken point to point with digital caliper under stereomicroscope and are expressed as percentages of standard length (SL) or head length (HL) for units of the head.
Frequency of a particular character value is presented in parentheses with the holotype value indicated by an asterisk.The scales of the median dorsal row and the small scales situated just below the insertion of the anteriormost dorsalfin ray are excluded from the counts of longitudinal scale rows between the dorsal fin and lateral line.Specimens were cleared and counterstained (c&s) following Taylor & Van Dyke (1985).Total vertebral counts were determined in c&s specimens.These include the first preural centrum plus first ural centrum (PU1+U1) counted as one element and the four vertebrae of the Weberian apparatus.Pleural ribs counted according to the vertebral counts (i.e., the rib of the fifth vertebra corresponds to the fifth rib).A key including all Chrysobrycon species, which was modified from Vanegas-Ríos et al. (2011), is provided on the basis of the examined material and data from literature (Böhlke, 1958;Weitzman & Thomerson, 1970).
Statistical tests and regression plots (as function of size) were performed using PAST 2.15 (Hammer et al., 2001) and SigmaPlot 10.0 for Windows (2006, Systat Software, Inc.) for measurements showing a sexually dimorphic pattern.The results of these analyses are presented in the section of sexual dimorphism.

Ecological notes.
The type locality is a white-water drainage with an average width of 3 m and depth between 0.3 and 1.6 m (very narrow shore).The water color is beige, rather clear and showing at least 20 cm of transparency.The velocity of current is moderate.The substrate is mainly sandy (80%) and covered by pebbles (20%).The riverine vegetation is mainly with its lateral face forming concave open pouch.Pouch with medial accessory scale somewhat curved, elongate and located under lateral face of pouch scale (partially visible in lateral view).Pouch with lateral accessory scale large, somewhat elongate posterodorsally and forming part of its laterodorsal region.Pouch scale and lateral accessory scale independent but in contact, both scales strongly attached to each other dorsally through well-developed medial mass of connective tissue.
Caudal-fin rays 15 to 18 and anterolateral surface of pouch scale of males with small pieces of apparent glandular tissue.
Gill gland of males relatively long and formed by fusion of anterior 12(1), 13*(2), 14(1), or 15(1) gill filaments of ventral limb of first gill arch.Total number of ventral limb gill filaments 25(1), 28(3), or 29*(1).Gill gland length between 4.7 and 6.9% SL (mean = 5.5% SL), 5.1% SL*.Snout to pectoralfin origin, snout to anal-fin origin, pectoral-fin to pelvic-fin Etymology.The new species name yoliae is matronym in honor and gratitude to "Yoli" (Yolanda Ríos Nossa), the mother of the senior author and who has patiently encouraged and supported his academic formation in all senses.  .some of its anatomical features related to the pouch scale have not been described in detail before.In a few mature males of C. hesperus and C. myersi, we observed a third accessory scale medially located on the posterior portion of the pouch scale, but its presence was variable through samples examined.

Key to
In mature males of Chrysobrycon eliasi, C. hesperus, and C. yoliae, the pouch scale and the lateral accessory scale are independent but in contact, with their dorsal borders strongly attached to each other through a variably developed mass of connective tissue.In matures males of C. myersi, the lateral accessory scale is short and without contact with the pouch scale, although both scales are connected through a soft portion of connective tissue in comparison with its congeners.
The presence of these types of accessories scales has a variable distribution among species of Stevardiinae with pouch scale in mature males.Some species of the Xenurobryconini have at least one accessory scale in mature males (e.g., Argopleura Eigenmann, Weitzman & Fink, 1985: 22); in this tribe, additionally, the term "accessories scales" was used for the scales situated posteroventral to the pouch scale (in a different position with respect to the accessories scales in Chrysobrycon species).In mature males of Pseudocorynopoma heterandria Eigenmann (Weitzman & Menezes, 1998: fig. 6), the pouch scale is accompanied by at least one ventral scale that may be interpreted as an accessory scale.In contrast, mature males of some species of Gephyrocharax Eigenmann, Pterobrycon myrnae Bussing and P. landoni Eigenmann (Bussing, 1974: figs. 5 and 6; Vanegas-Ríos et al., 2013a: fig.4) do not have these types of

Discussion
Chrysobrycon is a basal member of the tribe Xenurobryconini, phylogenetically diagnosed by the presence of a single large pouch scale with or without hypertrophied radii (Weitzman & Menezes, 1998).This is the only character supporting the position of Chrysobrycon within the tribe.The phylogeny and classification of the Xenurobryconini proposed by Weitzman & Menezes (1998) has been maintained in subsequent and related phylogenetic analyses mainly based on morphology (e.g., Castro et al., 2003;Mirande, 2010;Ferreira et al., 2011).Weitzman et al. (2005) considered that the origin of the pouch scale within the Xenurobryconini is homologous with that of the group named Stevardiini by Menezes & Weitzman (2009).Weitzman et al. (2005) stated that the pouch scale of mature males originates from the horizontal scale row just ventral to the lateral-line scale row.In Chrysobrycon species, the pouch scale seems to adjust to this pattern proposed by Weitzman et al. (2005).
We revised the morphology of the pouch opening of all species of Chrysobrycon and found some details not previously described in the literature (Weitzman & Thomerson, 1970;Weitzman & Menezes, 1998;Vanegas-Ríos et al., 2011).Species of Chrysobrycon are known by the possession of a single pouch scale and an additional scale situated under it, named in this paper as medial accessory scale (Weitzman & Menezes, 1998;Vanegas-Ríos et al., 2011).In addition to this, we found a lateral accessory scale that is located lateral to the pouch scale.Although this accessory scale has been illustrated in some figures presented by Weitzman & Thomerson (1970), Fig. 6.Detail of suspensorium of (a) Chrysobrycon yoliae, CI-FML 5882, paratype male, 44.8 mm SL, and (b) Chrysobrycon eliasi, paratype male, AI 287, 39.9 mm SL, comparing the posterior extent of ventral process of quadrate (QUA, white arrows) with respect to the vertical through posterior margin of symplectic (SYM, black arrows).Anterior to left.Scale bar = 1 mm.

Table 1 .
Morphometric data of holotype and 12 paratypes of Chrysobrycon yoliae (five males and eight females) from an unnamed Quebrada, río Yucamia system, Ucayali basin, Peru.SD = standard deviation.The values of the holotype are included in the range of males.