A new pale-spotted species of Hypostomus Lacépède ( Siluriformes : Loricariidae ) from the rio Tocantins and rio Xingu basins in central Brazil

A new species of the genus Hypostomus Lacépède (Siluriformes, Loricariidae) from rio Tocantins and rio Xingu basins in central Brazil, is described. The new species is distinguished from its congeners by a unique combination of pale blotches over a darker background on head, body and fins, and conspicuous keels on head, predorsal region and lateral plates. Comments on the pale-spotted species of Hypostomus are provided.

The new species reported herein was already known in the aquaristic literature as Hypostomus sp."honeycombpleco" (L37a, L161; Stawikowski, 1989;Glaser & Glaser, 1995;Stawikowski et al., 2004).During recent expeditions in central Brazil, a large number of specimens of this singular pale-spotted Hypostomus species was collected in the upper portions of rio Araguaia and rio Xingu basins, southern Brazilian tributaries of the lower portion of rio Amazonas.The aim of the present contribution is to describe the aforementioned undescribed species.

Material and Methods
Methodology and terminology for measurements follow Boeseman (1968) with the inclusion of the following measurements: preanal length, taken from snout tip to anal-fin origin; upper caudal-fin length, taken from last non-elongate dorsal caudal-peduncle plate to distal tip of uppermost caudal-fin ray; lower caudal-fin length, taken from last non-elongated ventral caudal-peduncle plate to distal tip of lower caudal-fin ray; adipose-fin spine length; body depth at dorsal-fin origin; snout-opercle distance, taken from snout tip to upper most portion of gill opening; mandibular-ramus length; premaxillary-ramus length; maxillary-barbel length, taken from anterior insertion of barbel to its tip.Plate counts and nomenclature follow schemes of serial homology proposed by Schaefer (1997), with the modifications of Oyakawa et al. (2005)

Color in alcohol.
Based only on specimens from the rio Tocantins basin.Dorsal and lateral surface of head and body with large, variously shaped but mainly rounded, paler blotches limited by narrow dark lines forming distinct net (or honeycomb) appearance (Figs. 1, 2a-b).Blotches on head slightly smaller than those on body, and less distinct towards caudal peduncle.All fins usually with similar color pattern (distal margins of fins with faded blotches or completely dark in some specimens).Color pattern of ventral surfaces of head and body ranging from similar to that on dorsal and lateral surfaces to uniformly grey, without blotches.Some specimens (e.g., MZUSP 87092, MZUSP 89390) showing two to five conspicuous oblique dark bars (called "stress coloration"; see picture in Glaser & Glaser, 1995: 63), first bar on posterior portion of head, originating at middle of orbit, second bar at first dorsal-fin branched rays, third bar at last dorsal-fin branched rays, fourth bar at adipose-fin and fifth at procurrent caudal-fin rays; these same specimens with pale band across interorbital area.

Geographical variation.
In the majority of the specimens from the rio Xingu basin the dark limits of coloration are larger when compared to specimens of the rio Tocantins basin, and the limits between pale blotches are about same size or slightly larger than the blotches .In Table 1.Morphometric data of Hypostomus faveolus.Letters in parenthesis correspond to measurements in Boeseman (1968: fig. 5).distribution map, since it likely represents an unnatural occurrence for the species (Fig. 3).
Etymology.From the latin faveolus, after favus, honeycomb.In allusion to the color pattern formed by the pale blotches with thin dark limits.An adjective.
Ecological notes.Hypostomus faveolus is a eurytopic species, and has been collected both in rapids and slow flowing portions of middle to large rivers, both in rocky and soft substrates.A few juvenile specimens were collected in small streams and oxbow lakes in the rio Culuene basin.

Discussion
There were no previous records for Hypostomus species with pale blotches over the body and fins in the Amazon basin.Hypostomus species that were recorded so far for the area belong to three main groups of species: the Hypostomus emarginatus group sensu Armbruster (2004), the Hypostomus cochliodon group sensu Armbruster (2003) and the Hypostomus plecostomus group sensu Muller & Weber (1992).addition, most small specimens (up to 50 mm SL) from the rio Xingu basin have pale blotches on the head forming vermiculations, whereas small specimens from the rio Tocantins basin show a pattern similar to that in adults.However, one lot of Hypostomus faveolus from the rio Suiá Miçu in the upper rio Xingu basin (MZUSP 86851) shows a color pattern more similar to specimens from the rio Araguaia basin.
Distribution.Hypostomus faveolus is known from several localities in the rio Tocantins basin and the upper rio Xingu basin in central Brazil.There is a single record for the species at the rio Meia Ponte, a tributary of rio Paranaíba, upper rio Paraná drainage in central Brazil.The rio Meia Ponte has its headwaters at the divide with the rio Araguaia basin, which might suggest a faunal interchange between the river basins.However, it is a common practice among recreational fishermen and ranchers from Goiânia area (the capital of Goiás state) to release fishes from the rio Araguaia basin in artificial ponds in the rio Meia Ponte catchment area (A.P. Fialho and F. Tejerina-Garro, pers. comm.).The eventual rupture of those ponds might explain why this and other fish species from the rio Araguaia basin, such as Hyphessobrycon moniliger (Characidae) and Pterygoplichthys joselimaianus (Loricariidae) were recorded in the last few years in the rio Meia Ponte basin.We have not included this locality in the All species assigned to these groups bear dark blotches over the body and fins.There is currently little information on the phylogenetic relationships within the genus Hypostomus, and, as a consequence, it is not possible to confidently assign Hypostomus faveolus to any monophyletic group within the genus.Muller & Weber (1992) defined a Hypostomus plecostomus species group by the common possession of an intermediate-sized dentary and teeth with short crowns, within which they placed, several species, including, H. commersoni, H. boulengeri, and H. plecostomus.Hypostomus faveolus shares with these species not only a similar tooth morphology, but also conspicuous keels on the head, predorsal region and lateral plates, and a fully plated abdominal area in adult specimens.Montoya-Burgos (2003) recognized four monophyletic groups within Hypostomus, one of which, his " D2", includes H. affinis, H. ancistroides, H. boulengeri, H. commersoni, H. plecostomus, H. punctatus, and H. watwata.This group corresponds to a potentially monophyletic Hypostomus plecostomus species group.More detailed phylogenetic studies on the genus, using both morphological and molecular data, are needed to corroborate this hypothesis.

Fig. 3 .
Fig. 3. Map of rio Tocantins, rio Xingu, and adjoining river basins, showing the geographic distribution of Hypostomus faveolus (type locality represented by open circle).
Diagnosis.Hypostomus faveolus is distinguished from its congeners by the unique combination of pale blotches over a darker background in body and fins (vs.dark blotches over paler background in body and fins, in most congeners), and conspicuous keels on head, predorsal region and lateral plates (vs.conspicuous keels absent in all remaining pale-spotted species of Hypostomus).See Discussion for additional notes on its diagnosis.Dorsal-fin base naked.Predorsal region with two conspicuous keels, area between keels flat.Dorsal series of lateral plates with keel from first plate to azygous plate before adipose fin.Mid-dorsal series of lateral plates with keel interrupted between third and fourth plate by ventral extension of first plate of dorsal series.Median series Description.Standard length of 234 examined specimens 22.6 to 206.0 mm.Measurements of holotype and paratypes in Table1.Overall view of body in Figures1 and 2. Dorsal profile convex from snout tip to dorsal-fin origin and almost straight from that point to end of adipose fin, then concave to caudal fin.Ventral profile almost straight from snout tip to caudal fin.Caudal peduncle in cross-section from trapezoidal on its anterior portion to elliptical posteriorly, slightly flattened dorsally and ventrally.Body width at cleithral region greater than head depth.Head broad, narrow anteriorly, covered dorsolaterally with dermal ossifications, except for small naked area on snout tip.Median elongated bulge associated with mesethmoid usually conspicuous from snout tip to transverse line between nares.Eye dorsolateral.Interorbital space Hypostomus species bearing pale blotches in the body and fins were previously recorded only from the río de La Plata (including rio Paraná, río Paraguay, and río Uruguay drainages), rio São Francisco and rio Paraguaçu basins.For the rio São Francisco basin two pale-blotched species are reported: H. alatus Castelnau and H. francisci (Lütken).The greatest diversity of pale-spotted species of Hypostomus occurs in the Río de La Plata basin, where the following species are recorded: H. albopunctatus (Regan), H. lexi (Ihering), H. luteomaculatus (Devincenzi), H. luteus (Godoy), H. margaritifer (Regan), H. myersi (Gosline), H. microstomus Weber, H. meleagris (Marini, Nichols & La Monte), H. multidens Jerep, Shibatta & Zawadzki, H. niger (Marini, Nichols & La Monte), H. roseopunctatus Reis, Weber & Malabarba, H. scaphyceps (Nichols), H. strigaticeps (Regan), H. tietensis (Ihering), and H. variipictus (Ihering).The sole Hypostomus species with pale blotches recorded for the eastern Brazilian river drainages is H. chrysostiktos Birindelli, Zanata & Lima, from the rio Paraguaçu basin in Bahia.All these pale-spotted Hypostomus species can be distinguished from Hypostomus faveolus by the absence of keels on the head, predorsal region and lateral plates.