A new armored catfish species of the genus Hypostomus Lacépède , 1803 ( Siluriformes : Loricariidae ) from the upper rio Xingu basin , Brazil

A new armored catfish species of the genus Hypostomus is described from the upper rio Xingu basin, Mato Grosso State, Brazil. The new species is diagnosed from congeners by having high number of teeth (58 to 101, mean 77 on premaxilla, and 58 to 105, mean 80 on dentary), dark spots over body and fins, and abdomen mostly naked. The new species is known from the rapids of the rio Culuene, where it is sympatric with Hypostomus faveolus.


Introduction
Hypostomus Lacépède, 1803 is the largest loricariid genus with 126 valid species (Weber, 2003;Hollanda Carvalho et al., 2010;Zawadzki et al., 2010).The genus Hypostomus is considered to be paraphyletic (Armbruster, 2004) and only diagnosable by symplesiomorphies.Hypostomus species are morphologically very conservative, and the relatively few diagnostic characters in external morphology and coloration within the genus usually vary intra-specifically in many species (Oyakawa et al., 2005;Zawadzki et al., 2008).This limited morphological variation and the high species richness represent a challenge to efforts aiming to clarify species boundaries among the species.Additionally, estimates based on molecular data (Weber, 2003), suggest that approximately one-third of all Hypostomus species are yet to be described.
Species of the genus Hypostomus occur in a wide range of habitats, from lowland lakes to fast running mountain streams (Burgess, 1989), and exhibit reproductive strategies as being egg guarders in which the male cares for eggs and larvae within some kind of cavity or nest (Suzuki et al., 2000).In addition, its sucker-like mouth allows them to feed on algae and detritus, an abundant resource in the Neotropics not available for the great majority of fishes.
Although the subfamily Hypostominae is highly diverse in the rio Xingu basin (e.g., Zuanon, 1999;Rapp Py-Daniel & Zuanon, 2005;Rapp Py-Daniel et al., 2011), there are few known species of Hypostomus for the basin.Recently, Zawadzki et al. (2008) described Hypostomus faveolus from the upper stretches of the rio Xingu and rio Tocantins basins.Sympatrically with Hypostomus faveolus at the rio Culuene in the upper rio Xingu basin, a second, undescribed Hypostomus species occurs which, unlike H. faveolus, is restricted to fastflowing, rocky river stretches.The aim of the present contribution is to describe that species.
Non-type specimens.Lower surface of head naked or with small patches of platelets immediately anterior to gill openings.Pectoral bridge usually with some platelets forming narrow transversal row.Abdomen usually with few platelets arranged only on lateralmost border, between pectoral-fin origin and pelvic-fin origin; a few larger specimens also with small patch of platelets on middle of abdomen (Fig. 3).
Dorsal fin II,7; moderate in size; spine flexible; its border strongly rounded; posteriorly reaching preadipose azygous plate when adpressed.Adipose-fin spine well developed, curved inward, with distal tip usually reaching anteriormost dorsal procurrent ray.Pectoral fin I,6; pectoral-fin spine slightly curved with rounded tip, and usually with distally well-developed odontodes, mainly in larger specimens; when adpressed reaching to approximately middle of pelvic-fin spine.Pelvic fin i,5; pelvic-  fin unbranched ray curved inward; when adpressed just reaching anal-fin insertion; its border almost straight.Anal fin i,4; when adpressed distal tip of posterior rays reaching fourth or fifth plate posterior to its origin.Caudal fin i,7+7,i; emarginate, with ventral lobe similar in length to slightly longer than dorsal lobe.
Color in alcohol.Ground color of dorsal surface of head and body dull brown.Head, dorsum and flanks covered with numerous dark round spots.Spots on head small, increasing gradually in size posteriorly, especially posterior to head.Spots more densely concentrated on snout and head.Some preserved specimens with overall dark coloration, without distinct dark spots.Ventral region of head and abdomen pale brown to grayish, usually without spots; spots only present as few isolated brown patches in few specimens.

Color in life.
Live specimens with coloration similar to preserved specimens, except that fins and ventral portion of head and body are yellowish brown (Fig. 4).
Etymology.Kuarup or Quarup, is an origin myth and a festivity shared by most the ethnical groups living in the upper portion of the Xingu Indigenous Park.The myth tells about a mythical hero, Mavutsinim, who wanted to bring the dead back to life.With this purpose in mind, he collected three logs of Kuarup wood and after adorning them, he asked a cane toad and an agouti, as well as his tribal men, to sing and dance by the logs, as they would turn into bodies for the deceased.The ceremony ultimately failed in the last phase, but Mavutsinim declare that from then on the festivities should be carried in honor of the deceased (Villas Boas & Villas Boas, 1986).The Kuarup festivity takes places between July and September, when the different ethnical groups of the upper Xingu gather in one village and for several days dance, sing around tree trunks that represent the dead man, and perform the famous huka-huka wrestling contests.The first Kuarup is said to have taken place at the Saginhenhu, a locality recently identified by the Indians as being the Cachoeira do Adelino, one of the localities from where Hypostomus kuarup is known.

Distribution and habitat.
Hypostomus kuarup is known from the rio Culuene, upper rio Xingu basin, Mato Grosso, Brazil (Fig. 5).The species is the most abundant loricariid catfish in the area, though, unlike the sympatric congener Hypostomus faveolus (Zawadzki et al., 2008: 400), H. kuarup is confined to rapid stretches.The type locality was a former rapid that was dried out after the building of the Paranatinga II hydroelectric Dam (Fig. 6).The species still persists at a fish ladder built at the type locality (CPUFMT 656) and certainly also at rapids situated both above (at the mouth of the rio Maria) and below the reservoir (Cachoeira do Adelino).
Remarks.Hypostomus kuarup is known from thousands of specimens collected in the rio Culuene in the former rapids,  current area of reservoir Paranatinga II (13°51'03"S 53°15'31"W), and tributaries of rio Culuene nearby.As the number of specimens is too large, a sample of 60 specimens from the aforementioned locality was chosen to constitute the type series.

Discussion
The high number of teeth in the upper and lower jaws of Hypostomus kuarup (premaxilla 58-101, mean = 77; and dentary 58-105, mean 80) is a key character of the new species.This character readily distinguish it from the species of the Hypostomus cochliodon group, H. plecostomus and related species from Suriname and Guianas, which have less than 60 teeth on each upper and lower jaw (Boeseman, 1968;Planquette et al., 2000).All aforementioned species also differ from Hypostomus kuarup by having abdomen mostly plated (vs.abdomen almost completely naked in the new species).Most species of Hypostomus with high number of teeth (up to 100) (H.alatus, H. francisci, H. multidens, H. regani, and H. Table 1.Morphometric data of Hypostomus kuarup.Letters in parenthesis follow the abbreviations of Boeseman (1968).N = number of examined specimens, SD = standard deviation.snout (Fig. 7).Molecular (P.Hollanda-Carvalho, pers.comm.) and cytogenetic (L.Giuliano-Caetano, pers.comm.)evidence shows Hypostomus mutucae to be related to an assemblage of Hypostomus from the rio Paraguay basin that includes H. latirostris and H. ternetzi.Although the relationships of Hypostomus kuarup are at the moment unknown, we suspect that the species might be related to several undescribed Hypostomus species occurring at the southern shield tributaries of the Amazon basin.
Hypostomus kuarup is also characterized by having only slightly developed keel-like rows formed by moderately enlarged odontodes on body plates.This feature contrasts with the condition present, on one hand, in Hypostomus species as H. carinatus, H. commersoni, H. hoplonites, and H. plecostomus, which possess distinct, well-developed keels on the body plates, and, on the other hand, from species as H. agna, H. garmanni, H. hermanni, and H. pyrineusi, which have smooth body plates which entirely lack keels.Another interesting feature of the new species, shared with congeners which also exhibit preference for habitats with rocky bottom and fast flowing water, is its naked abdomen (mostly without plates) in specimens from all sizes.As earlier recorded by Gosline (1947) and Boeseman (1968), fully plated ventral areas are usually present in middle to large specimens of most species of Hypostomus, but are almost completely lacking throughout the whole life of a few species.BMNH 1892.4.20.26-27, syntypes, 2, 137.2-159.3 mm SL, rio Jangada, rio Paraguay basin. Mato Grosso State: NUP 11014, 4, 113.3-153.3São Paulo State: BMNH 1907.7.6.1012, syntypes, 3, 75.7-160.0 mm SL, rio Piracicaba, rio Tietê basin. NUP 4017, 2, 72.8-100.0 mm SL, rio Ipanema, rio Tietê basin, Ipuã. NUP 4538, 11, 82.0-140.0

Fig. 2 .
Fig. 2. Head and anterior portion of body in lateral view of Hypostomus kuarup, MZUSP 94864, 147.0 mm SL.Inset box on upper left corner show detail of odontodes development on cheek plates.

Fig. 6 .
Fig. 6.Type locality of Hypostomus kuarup, Brazil, Mato Grosso, rapids at rio Culuene (currently dry by the diversion of the river channel due to the construction of the Paranatinga II hydroelectric dam).Photo taken during the early dry season.