Parotocinclus seridoensis , a new hypoptopomatine catfish ( Siluriformes : Loricariidae ) from the upper rio Piranhas-Açu basin , northeastern Brazil

A new species of Parotocinclus is described from the upper rio Piranhas-Açu basin, northeastern Brazil. The new species differs from all its congeners, except P. bidentatus, P. muriaensis (both from rio Paraíba do Sul basin, southeastern Brazil), and P. spilurus (rio Jaguaribe basin, northeastern Brazil) by presenting the adipose fin rudimentary or absent. The new species differs from P. bidentatus, P. muriaensis, and P. spilurus mainly by presenting the abdomen region extensively naked, with few reduced rounded dermal platelets between the pectoral girdle and the anus. Parotocinclus seridoensis is probably an endemic species of the semi-arid Caatinga, region where the genus presents high species richness.

Parotocinclus was originally described as a monotypic subgenus of Hisonotus by Eigenmann & Eigenmann (1889), and the same authors (1890) raised its condition to the genus level, mainly due to the presence of an adipose fin.Schaefer (1991) recognized the genus as monophyletic, using three putative characters: 1) robust short crest on hyomandibula separating the adductor mandibulae of the cheek from the dilator and levator operculi muscles; 2) first dorsal-fin spinelet large, and 3) lateral line interrupted, terminating two to four plates preceding the last lateral plate.However, according to morphological parsimony phylogenetic analysis Parotocinclus was recognized as a polyphyletic assemblage (Gauger & Buckup, 2005).Lehmann (2006) also recognized the genus as a highly paraphyletic group of species, thus needing a formal revision and the erection of new genera to accommodate the species previously assigned to Parotocinclus, but not closely related to the type species P. maculicauda (Steindachner).

Material and Methods
Specimens were fixed in formalin for approximately two weeks, and then transferred to 70% ethanol.Measurements and counts followed Carvalho & Reis (2009).Counting of longitudinal plate series followed Britski & Garavello (2009), while osteological nomenclature followed Schaefer (1997).Measurements were taken with a digital caliper, and recorded to tenths of a millimeter.Descriptions of color pattern are based on photographs of live individuals kept in aquaria after collection.Measurements are presented as percents of standard length (SL) or head length (HL).Osteological examinations were performed on cleared and double-stained for bone and cartilage (c&s) specimens according to the procedure of Taylor & Van Dyke (1985).Vertebral counts included all vertebrae of the Weberian apparatus and the compound caudal centrum (PU1+U1) counted as a single element.Plates at dorsal-fin base 5 4-5 5 Plates at anal-fin base 2 2 2 Plates between anal and caudal fins 10 10 10 Table 2. Meristic data of holotype (MZUSP 113422) and 24 paratypes of Parotocinclus seridoensis.
In addition to the adipose fin rudimentary or vestigial Parotocinclus seridoensis is further distinguished from congeners of northeastern Brazil, except P. arandai, P. cearensis, P. cesarpintoi, P. jumbo, P. minutus, and P. spilosoma, by having abdomen nearly naked, with only one or two row of plates on each side and median row of platelets irregularly distributed (vs.abdomen entirely covered by larges plates between the pectoral girdle and preanal region in P. cristatus, P. jimi, and P. haroldoi, and abdomen completely naked with only preanal platelets in P. bahiensis).Parotocinclus seridoensis also shares with P. bahiensis, P. cearensis, and P. jumbo the pectoral girdle covered by skin medially and laterally exposed, and supporting odontodes only laterally (vs.scapular bridge completely exposed in P. arandai, P. cesarpintoi, P. cristatus, P. jimi, P. haroldoi, P. minutus, and P. spilosoma).
Description.Morphometric and meristic data of holotype and paratypes are presented in Table 1 and 2. Body up to 42.6 mm SL.Body moderately short and somewhat depressed.Greatest body width at cleithrum, progressively tapering to end of caudal peduncle.Dorsal profile slightly convex from snout to parietosupraoccipital tip; straight between parieto-supraoccipital and dorsal fin origin; descendent at dorsal-fin base; slightly concave from dorsal-fin end to rudimentary adipose fin (or azygous plate indicating its position); straight or slightly concave from this point to base of uppermost caudal-fin rays.Ventral body profile of head straight or slightly concave; ventral profile of trunk somewhat straight from pectoral girdle to posterior base of pelvic fin; somewhat concave at anus region, straight at anal-fin base and straight from anal-fin end to lowermost caudal-fin rays.Head depressed and round in dorsal view.Eyes moderately small, positioned midway between snout tip and pterotic-supracleithrum posterior margin; distance between orbit margin and ventral surface of head greater than orbital diameter.Dorsal iris diverticulum present.Interorbital space straight or slightly convex.Pectoral girdle exposed only laterally; median region covered by skin (Fig. 3); coracoids laterally covered by odontodes; arrector fossae ellipsoid, small, extending laterally, almost meeting in at midline (Fig. 4).Snout rounded in dorsal view.Greatest body depth at dorsal-fin origin.Individuals with two depressions on snout; inferior rostral margin of snout with posteriorly directed odontodes similar in size to those on dorsal portion of snout, sometimes with an area variable in extension deprived of odontodes at the anteroventral border of snout shaped as an inverted V or U. Odontodes on upper part of head, roughly arranged in rows.Mouth small.Oral disk approximately round, papillose; maxillary barbels slightly shorter than orbital diameter.All teeth slender and bifid.Accessory patch of uniscupid teeth absent.Head depressed and round in dorsal view.Eye moderately small and dorsolaterally positioned; distance between ventral margin of orbit and ventral surface of head greater than orbital diameter.Trunk depressed on insertion of dorsal and anal fin.Caudal peduncle rounded in cross section.Dorsal fin i,7; its origin slightly posterior to pelvic-fin origin; dorsal fin when adpressed extending to vertical through Fig. 2. Parotocinclus seridoensis, live paratype specimen, UFRN 240, 30.6 mm SL, from rio Seridó (type locality), Caicó, Rio Grande do Norte, just after collection.
Coloration.Ground color in ethanol dark gray to dark brown.Dorsal and lateral portions of head uniform in color with a bright spot on pineal region; ventral area of head yellowish.Trunk with clear spots, usually uniform in size, diameter, form (usually rounded) and distribution, forming sometimes two alternate longitudinal series, dorsally and ventrally, extending from gill opening to caudal peduncle, ending in two conspicuous whitish yellow blotches vertically arranged.Abdomen yellowish white, anterior region (pectoral girdle to anus) with little dark chromatophores, posterior region with conspicuous dark chromatophores.Dorsal and caudal-fin rays with dark chromatophores, forming irregular set of stripes that alternates between dark gray and brownish yellow: three on dorsal fin and four on caudal fin; tip of caudal-fin lobes intensively pigmented with dark chromatophores.Pectoral, pelvic-and anal-fin rays with few and sparse chromatophores forming a set of inconspicuous stripes.Live coloration (Fig. 2) with same pattern described above, only becoming clearer in fixed specimens.
Sexual dimorphism.Males possess urogenital papilla positioned just behind the anal opening and a low fleshy flap along the dorsal margin of the first pelvic-fin ray, that is absent in females.
Distribution.Parotocinclus seridoensis is only known from four localities in the upper rio Piranhas-Açu basin, which is formed by two main tributaries, the rio Piranhas itself in the west, and the rio Seridó in the east, in the boundaries of Rio Grande do Norte and Paraíba States.Individuals of the new species were mainly found in rio Seridó, in Caicó Municipality, and in rio Piranhas main channel at Pombal Municipality, while a single specimen was caught in rio Piranhas, Jardim de Piranhas Municipality, upstream the confluence with the rio Seridó, and another in the rio Piancó, Ibiara Municipality, the southernmost record of the species, suggesting a restricted geographic distribution (Fig. 5).
beyond anal-fin base.Pectoral fin i,6; pectoral spine reaching one quarter to one third of length of unbranched pelvic-fin ray.Pelvic-fin rays i,5; unbranched ray curved, covered with small odontodes; pelvic fin reaching beyond anus, ending just anterior to anal-fin origin.Anal-fin rays i,5; origin of anal fin covering three plates.Caudal fin slightly notched, emarginate, with lower lobe slightly pointed and longer upper lobe; principal caudal-fin rays i,14,i.Lateral-line canal in median series complete, pore tube visible from pterotic-supracleithrum to caudal peduncle.Abdomen nearly naked; with only one or two row of small plates elongate and rounded on each side arranged near the pectoral girdle, and a group of small rounded plates irregularly distributed on preanal region (Fig. 3); some young individuals with two or three platelets in the middle of abdomen.Dorsal-fin spine flexible, followed by seven branched rays.Dorsal-fin locking mechanism nonfunctional.Nuchal plate exposed, not covered by skin.Dorsal-fin spinelet present, V-shaped, wider than base of dorsal spine.Adipose fin rudimentary or vestigial.Total vertebrae 24 (2 c&s).this microhabitat was found only at the right margin, where P. jumbo was observed forming small shoals, behavior already registered by Britski & Garavello (2002).
During ichthyological surveys in the upper rio Piranhas-Açu, some of the above mentioned species were only found in fast-flowing rivers, just as the rio Piranhas at Jardim de Piranhas, and the rio Seridó at Caicó, both temporary rivers made perennial by water release from Açude de Coremas and Passagem das Traíras dams, respectively.With the river disconnection by weirs and dams constructions, it is possible Etymology.The species epithet seridoensis refers the semiarid Caatinga region, popularly known as "Sertão do Seridó", which encompasses the upper rio Piranhas-Açu basin region in Rio Grande do Norte and Paraíba States, one of the most arid regions in northeastern Brazil, with mean annual rainfall of about 500 mm (Silva et al., 2006).The etymology of the word "Seridó" is probably derived from the native Indian language expression "ceri-toh".In Tapuia language it means "little foliage and little shade", referring to the characteristic Caatinga vegetation, mainly composed by xeric shrub lands and thorn forest, that consists in small, thorny trees that shed their leaves in the dry periods.
Ecological notes.Specimens were caught in rio Seridó, type locality of the species (Fig. 6), and in the rio Piranhas, both tributaries of the upper rio Piranhas-Açu basin.The "Sertão do Seridó" region is characterized by temporary rivers, due to small precipitation concentrated in few months of the year and high temperatures and evaporation (Rosa et al., 2003).Parotocinclus seridoensis was usually found under large rocks in streams of moderate current flow and clear water (Fig. 6).In these, Parotocinclus jumbo, was found in sympatry, however, inhabiting shallow and narrow streams with laminar flow, sand and gravel substrate, in the rio Seridó, while in the rio Piranhas several species in the receiving basins, changes in the structure and composition of aquatic communities, species hybridization, loss of local adaptations, and local extirpation or extinction of endemic species (Langeani et al., 2009), just as P. seridoensis.

Discussion
Pending an ongoing phylogenetic study involving the relationships within the Loricariidae, including the Hypoptopomatinae, and a redefinition of Parotocinclus and allied genera, the new species is herein assigned to Parotocinclus.According to Lehmann (2006), P. seridoensis (identified as Parotocinclus sp.n. 10) is closely related to P. cesarpintoi, P. haroldoi, and P. spilurus, all species from the northeastern Brazil.
Although the presence of adipose fin is traditionally used as a diagnostic feature of Parotocinclus, a rudimentary or absent adipose fin was also observed in P. bidentatus, P. muriaensis, and P. spilurus (Fowler, 1941;Gauger & Buckup, 2005).In these species the adipose fin is represented by two small unpaired plates (Gauger & Buckup, 2005) forming a vestigial that these artificially perennial river stretches could represent important role in maintaining populations of rheophilic species that couldn't reach the headwaters upstream during dry periods.
Gastrointestinal contents of two specimens of P. seridoensis was mainly composed by benthic invertebrates (Chironomidae and Coleoptera larvae) in one specimen (UFRN 005, 30.7 mm SL), while the other presented the tract filled with silt (UFRN 1590, 35.4 mm SL).
Conservation remarks.The rio Piranhas-Açu basin is one of the largest temporary rivers of the semi-arid northeastern Brazilian area, constantly affected by drought, that will receive water from the controversial project of the artificial watershed transposition of the perennial rio São Francisco (Lima, 2005).Although it could ensure water supply to rural and urban local people, diverting water from the rio São Francisco basin can cause many harmful environmental impacts to the aquatic biota of the river basins of the Mid-Northeastern Caatinga region, which encompasses the basins east to rio Parnaíba and north to rio São Francisco (Rosa, 2004;Abell et al., 2008).Among these potential impacts to the aquatic organisms are: the intake of this analysis P. spilurus, the single species described at the time with rudimentary adipose fin, was not included.Parotocinclus seridoensis differs from P. bidentatus, P. muriaensis and P. spilurus by presenting the abdomen almost entirely naked (Fig. 3), having only a single row of reduced elongate plates on each side and a few rounded platelets irregularly distributed on the preanal region, while P. bidentatus, P. muriaensis and P. spilurus have conspicuous lateral plates and abdomen mostly covered by plates.
Most individuals of P. seridoensis also present an area deprived of odontodes at the anterior border of the snout shaped as an inverted V or U, a feature discriminating individuals of the new species from P. spilurus whose anterior border of the snout is covered by regular rows of odontodes (Fig. 7).
Parotocinclus spilurus and P. seridoensis occur in adjacent river basins of the Mid-Northeastern Caatinga region, the former from the rio Jaguaribe basin and the latter from the rio Piranhas-Açu basin.Although these are the largest and main hydrographic basins of this region, both species are apparently restricted to the upper portions of the rio Jaguaribe and Piranhas-Açu basins, respectively.If the above mentioned characters represent synapomorphies between P. spilurus and P. seridoensis, indicating a sister-species relationship, it is possible that a vicariant process, due to common tectonic activation in northeastern Brazil (Lima, 2000;Bezerra et al., 2006), around the Chapada de Apodi region, the watershed divide between rio Jaguaribe and Piranhas-Açu basins, could be involved in the origin of these species.A similar pattern of closely related species found in the same area is the occurrence of Pseudoancistrus genisetiger Fowler in rio Jaguaribe basin and P. papariae in rio Piranhas-Açu basin.
Of the 27 Parotocinclus valid species so far described, twelve occur in northeastern Brazil, representing approximately 44.4% of the known species (Sarmento-Soares et al., 2009;Lehmann & Reis, 2012).Among these species, five occur in eastern Atlantic coastal basins (P.arandai, P. bahiensis, P. cristatus Garavello, P. jimi Garavello, and P. minutus), six in Mid-Northeastern Caatinga region (P.cearensis, P. cesarpintoi, P. jumbo, P. seridoensis, P. spilosoma, and P. spilurus), and one in the rio Parnaíba basin (P.haroldoi).The two species known from rio São Francisco basin (P.prata and P. robustus) were only recorded from tributaries of the upper and middle portions of the basin, in Minas Gerais State, southeastern Brazil (Lehmann & Reis, 2012).ridge, although it is usually slightly more developed, and easily to be observed in lateral view, in P. spilurus than in P. seridoensis.Parotocinclus bidentatus and P. muriaensis were described from the rio Paraíba do Sul basin, and differ from most species of Parotocinclus, including P. seridoensis and P. spilurus, by the presence of accessory unicuspid teeth located internally to the series of bicuspid teeth on premaxillary and dentary bones (Gauger & Buckup, 2005).

Fig. 5 .
Fig. 5. Geographic distribution of Parotocinclus species in Mid-Northeastern Caatinga region and rio Parnaíba basin, northeastern Brazil.Open symbols represents type localities.
Diagnosis.The new species differs from all its congeners, except Parotocinclus bidentatusGauger & Buckup, P. muriaensis Gauger  & Buckup and P. spilurus (Fowler)by presenting adipose fin rudimentary or absent.Parotocinclus seridoensis differs from P. bidentatus, P. muriaensis and P. spilurus by presenting abdomen almost naked, with a single row of elongate reduced plates on each side and a group of small rounded plates irregularly distributed on preanal region (vs.abdomen completely covered of dermal plates between the pectoral girdle and the anus), and also by presenting bright spots, usually about as large as the eye diameter or larger on sides of the body predominantly disposed in two rows (dorsally and ventrally) (vs.body without spots in P. bidentatus and P. muriaensis; and with numerous small bright spots about as large as pupil diameter scattered on body and head in P. spilurus).Parotocinclus seridoensis also differs from P. bidentatus and P. muriaensis, but not to P. spilurus by the presence of of pectoral girdle medially covered by skin and laterally exposed, supporting odontodes only laterally (vs.completely exposed).It also differs from P. spilurus by the presence of an area deprived of odontodes at the anterior border of the snout shaped as an inverted V or U (vs. anterior border of the snout covered by regular rows of odontodes).