A new species of Hypostomus Lacépède, 1803 (Siluriformes: Loricariidae) from the upper rio Paraná basin, Southern Brazil

A new species of Hypostomus with large and spaced light roundish spots is described from the upper rio Paraná basin. Hypostomus multidens new species is distinguished from all remaining congeners with light spots on a darker background by two independent characters: the presence of teeth with two symmetrical cusps, and a high tooth number in each dentary (122267, mean 196.8) and premaxilla (115-260, mean 190.8).


Introduction
Presenting practically the same range of the family Loricariidae throughout Central and South America, the Hypostominae is the largest subfamily, with about 31 genera and 366 valid species (Armbruster, 2004).The genus Hypostomus Lacépède, 1803 is one of the most diverse and complex groups of South American catfishes, due mainly to incomplete species descriptions, limited knowledge about their distribution patterns, and the particularly high intraspecific variability in morphology and color pattern (Reis et al., 1990;Weber, 2003).Regional revisionary studies are an alternative used for some authors to deal with the complex taxonomical questions of Hypostomus, as demonstrated by Boeseman (1968) for the species from Suriname, Weber (1985Weber ( , 1986Weber ( , 1987) ) for Hypostomus from Paraguay, Reis et al. (1990) for species from Southern Brazil, Mazzoni et al. (1994) for species from lower rio Paraíba do Sul, in the State of Rio de Janeiro, Hollanda Carvalho & Weber (2004) for the Hypostomus cochliodon group from middle and lower Amazon system, and Oyakawa et al. (2005), for Hypostomus from rio Ribeira de Iguape drainage, in the States of São Paulo and Paraná.
The main objective of this study is the description of a new species of Hypostomus from the upper rio Paraná basin.A complete review of the nominal species of Hypostomus from the rio Tietê basin, including the presentation of an identification key is currently being prepared by C. H. Zawadzki, H. A. Britski and C. S. Pavanelli (pers. comm.).The new species described herein is included in the group of species with light roundish dots on a darker background.

Material and Methods
All measurements were taken point to point with digital calipers to the nearest 0.1 mm, under a dissecting microscope when necessary.Measurements and counts of bilaterally symmetrical features were taken from the left side of the body whenever possible; if a feature was missing or broken on the left side, it was examined on the right side.
Measurements follow Weber (1985), Fisch-Muller et al. (2001), andPereira &Oyakawa (2003).Counts and nomenclature of median plate series were taken according to Schaefer (1997) with the modifications of Oyakawa et al. (2005).Additional measurements and counts include: eye-nostril distance (least distance between anterior orbital margin and nostril), plates between dorsal and adipose fins (number of plates in dorsal series between insertion of last dorsal-fin branched ray and origin of adipose-fin spine), and plates between adipose and caudal fins (number of plates in dorsal series from just posterior to the adipose-fin membrane to the caudal fin).In case of missing teeth, the space left was counted as a tooth.Standard length (SL) is expressed in mm.All other measurements are expressed as percents of standard length, except subunits of the head, which are expressed as percents of head length (HL).Scanning Electron Microscope (SEM) images were obtained from teeth.
The specimens examined belong to the American Museum of Natural History, New York (AMNH), The Natural History Museum, London (BMNH) Greatest body depth at dorsal-fin origin.Ventral surface of head usually naked, sometimes with platelets anterior to gill openings; abdomen covered with minute platelets at line of pectoral girdle and anterior of urogenital opening, some specimens with plated area expanded to center of abdomen.Head broad, anterior profile roundish or moderately roundish in dorsal view.Snout depressed with naked area without odontodes on its tip.Three slightly longitudinal ridges between orbits and snout tip, lateral ridges more prominent.Dorsal region between orbits concave; upper margin of orbits elevated.Supraoccipital bordered posteriorly by first predorsal plate, its dorsal surface convex with ridge that increases through predorsal plates until dorsal-fin origin.Dorsal plates between end of dorsal-fin base and first unpaired preadipose plate flattened; first ones without odontodes on their median line.Mid-dorsal and medial series of plates more keeled until middle of dorsal-fin base.Mid-ventral series of plates keeled until beginning of ventral series of plates.First anal-fin proximal radial exposed, forming flat plate anterior to first anal-fin ray.Most lateral body plates with weak odontodes on posterior border.
Eye moderately large, dorsolaterally placed.Iris with minute dorsal flap covering pupil.Mouth with short, narrow buccal papilla.Oral disc wider than longer and well developed, occupying most of ventral surface of head.Lower lip reaching gill opening and covered with minute papillae, that decrease in size towards lips edge.Maxillary barbel short, coalesced with lower lip and ornamented with small papillae.Teeth thin, bicuspid with symmetrical cusps, in high number and very small size; slightly curved inwards (Fig. 2).Opercular region not very mobile, with few hypertrophied odontodes.Cleithrum exposed and in contact with ventral border of pteroticsupracleithrum, pointed cleithral process extending above pectoral-fin insertion.
Nuchal plate present; dorsal-fin spinelet present and locking mechanism functional.Dorsal-fin origin at vertical line halfway from pectoral to pelvic-fin insertions.Last branched dorsal-fin ray reaching adipose-fin spine.Dorsalfin spine moderately flexible on distal portion.Adipose fin present and slightly curved, preceded by unpaired pre-adipose azygous plates.Pectoral-fin spine slightly curved, with hypertrophied odontodes curved forward on its distal tip.First and second branched rays as long as spine.Subsequent branched rays gradually decreasing in size.Posterior margin of pectoral fin straight, surpassing about one third of pelvic fin when adpressed.Pelvic-fin spine reaching first half of anal fin when adpressed, covered with minute odontodes ventrally and laterally.Posterior margin of pelvic fin slightly roundish.First anal-fin ray unbranched, reaching sixth plate after its origin.Distal profile of caudal fin concave, lower lobe longer than upper.
Color in alcohol.Ground color of dorsal surface of head and body brown or grayish brown; pale yellow ventrally.Dorsal surface of head with blotches slightly smaller and closer to each other than those on posterior portion of body.Dorsum and flanks covered with light roundish blotches, equally spaced and with almost pupil size.Blotches present on fins, including interradial membranes.Ventral margin of head and outer portion of upper lip homogeneously light brownish; ventral portion of caudal peduncle dusky.Spines of dorsal, pectoral, pelvic, anal and caudal fins grayish brown (Fig. 3).Color in life.Ground color of upper surface of head and body black or grayish black; pale gray ventrally.Blotch color ranges from vibrant yellow to orange.
Distribution.Hypostomus multidens is known from several localities in the rio Paranapanema basin in the states of São Paulo and Paraná.It was also found in the rio Paraná in the transition from rapid to still waters at the beginning of the Itaipú Reservoir lake in the city of Guaíra (Fig. 4).
Etymology.The specific epithet multidens (Latin) is given in allusion to the high number of teeth (multus, many + dens, teeth).

Discussion
Tooth morphology and the high number of teeth, both distinguish Hypostomus multidens from all remaining species of Hypostomus (Fig. 2).Notwithstanding, H. multidens can also be recognized by the concurrent presence of non-exclusive characters, such as: the color pattern; stout body; short, flat and round snout; large eyes with orbital ridges; a ridge on supraocciptal plates; large mandible (21.3 to 28.7% HL); and high number of weak odontodes on the body plates (Fig. 1).
Hypostomus multidens is very similar to the H. ternetzi species group (Zawadzki et al., 2005) in external morphology.Despite the dark spots present in the species of that group, H. multidens match all external morphological traits proposed by those authors, including wide jaw, deep caudal peduncle, supraoccipital process and predorsal plates forming a medium crest, and abdominal plates restricted to the anterior portion of the abdomen or with extensive naked areas around pelvicfin insertions.
The large and widely-spaced light spots (Fig. 3) not only distinguish H. multidens from the dark spotted species from the upper rio Paraná basin (H. ancistroides, H. brevis, H. commersoni, H. fluviatilis, H. hermanni, H. iheringii, H. nigromaculatus, H. paulinus, H. ternetzi and H. topavae), but also from the Hypostomus with small closely-spaced light spots (H. albopunctatus, H. lexi, H. margaritifer, H. meleagris, H. regani, H. scaplyceps, H. strigaticeps, H. tietensis and H. variipictus) present in the same basin.Among the species with light spots on a darker ground, only H. microstomus have a similar spot pattern, but differs from H. multidens in tooth shape (stout teeth with asymmetric cusps) and low teeth number (approximately eight to 16, according to Weber, 1987).
Tooth shape is also variable among hypostomines, and some extreme forms characterize taxa (Muller & Weber, 1992).The presence of teeth with two symmetrical cusps in Hypostomus multidens is a feature absent in all known species of Hypostomus, whose teeth have two asymmetrical cusps.Symmetrical cusps is not common among the Loricariidae, and in his phylogenetic analysis of the loricariid subfamilies, Schaefer (1987) considered the symmetrically-bifid teeth of Astroblepidae primitive relative to the derived asymmetrically bifid teeth of Loricariidae.Although almost symmetricallybifid teeth are also present in the basal loricariid subfamilies Lithogeninae (Provenzano et al., 2003;Schaefer, 2003) and Delturinae (Reis et al., 2006), the presence of a similar structure in H. multidens is not necessarily evidence that we are dealing with a basal species.According to the most recent phylogenetic analyses including the Loricariidae subfamilies (Armbruster, 2004;Reis et al., 2006), it is more parsimonious to consider the presence of symmetrically-bifid teeth in a Hypostomus species a homoplastic feature, rather than the maintenance of a plesiomorphic character or closer relationship between derived Hypostominae and basal Lithogeninae and Delturinae.
Despite some evidence, the position of H. multidens inside Hypostomini and its connection with H. ternetzi group, is yet to be evaluated in a phylogenetic study that includes the species of Hypostomus.

Fig. 2 .Fig. 3 .
Fig. 2. SEM photographs of Hypostomus multidens left dentary teeth.Partial ventral view of dentary (a).Ventral view of emergent teeth rows (b).Lateral view of teeth symmetrical cusps (c).Frontal view of tooth crown with symmetrical cusps (left), and lateral view of tooth crown with partially broken cusp (d).All photographs were taken from the paratype MZUEL 4497, 177.3 mm SL, same data as holotype.

Fig. 5 .
Fig. 5. Box plots of the number of dentary and premaxillary teeth (n = number of specimens analyzed).

Table 1 .
Morphometrics and meristics data of the holotype and paratypes of Hypostomus multidens (N = 26 including the holotype).