Pareiorhaphis nasuta, Pereira & Vieira & Reis, 2007

Pereira, Edson H. L., Vieira, Fábio & Reis, Roberto E., 2007, A new species of sexually dimorphic Pareiorhaphis Miranda Ribeiro, 1918 (Siluriformes: Loricariidae) from the rio Doce basin, Brazil, Neotropical Ichthyology 5 (4), pp. 443-448 : 445-447

Pareiorhaphis nasuta , new species

Fig. 1 , Table 1

Holotype. MCP 41764, 78.6 mm SL, male; Brazil: Minas Gerais: Abre Campo: District of Granada: ribeirão Areia Branca , tributary to the hydroelectric dam Túlio Cordeiro de Mello , rio Matipó basin, rio Doce drainage, 20°11’17"S 42°22’27"W, 9 Oct 2004, E. H. L. Pereira, R. E. Reis & P. Lehmann.

Paratypes. Brazil: Minas Gerais: rio Doce drainage: MCP 37176, 10 + 2 c&s (9) 25.1-78.6 mm SL; collected with the holotype. MCP 38809, 11 (7) 45.3-94.7 mm SL; rio Matipó , Distrito de Granada, Abre Campo, 20°11’00"S 42°23’00"W, 17-20 Aug 2002, F. Vieira. MCP 38807, 3 (2) 39.8-63.4 mm SL; ribeirão Areia Branca, tributary to rio Matipó, Abre Campo, 20°11’15"S 42°22’26"W, 29 Jul 2004, F. Vieira. MCP 38808, 10 + 1 c&s (6) 50.2-93.7 mm SL; ANSP 187153 , 2 (2) 67.9-87.3 mm SL; and MZUFV 2567 , 3 (2) 65.4-84.1 mm SL; rio Matipó at Raul Soares, 20°07’23"S 42°24’51"W, 1997, J. A. Dergam .

Diagnosis. Pareiorhaphis nasuta is distinguished from all congeners by the longer snout (71.1-75.6 vs 52.8-69.9% HL). Additionally, the smaller orbital diameter (8.6-11.3 vs 11.7-18.8% HL) further distinguishes P. nasuta from most other Pareiorhaphis species , except for P. garbei , P. vestigipinnis , P. cerosus , and P. splendens . Pareiorhaphis nasuta is further distinguished from P. garbei by having bifid teeth, with a small lateral cusp in both dentary and premaxilla (vs simple teeth, without lateral cusp in both dentary and premaxilla); from P. vestigipinnis by having an adipose fin (vs adipose fin absent); from P. cerosus by having one to three preadipose azygous plates (vs three to five plates); and from P. splendens by the longer pelvic-fin spine (19.4-23.4 vs 12.6-19.1% SL).

Description. Counts and proportional measurements in Table 1. Standard length of measured specimens 55.5-94.7 mm SL. See Fig. 1 for general body aspect. Body elongate and moderately depressed, progressively narrowing from cleithrum to end of caudal peduncle. Dorsal profile of body gently convex, rising from snout tip to origin of dorsal fin and then descending to end of caudal peduncle. Greatest body depth at dorsal-fin origin. Least body depth at shallowest part of caudal peduncle. Trunk and caudal peduncle mostly oval in cross-section, slightly flattened ventrally and more compressed caudally. Lateral-line canal in median series complete, pored tube visible from compound pterotic to caudal-fin base. Ventral profile almost straight between snout tip and pelvic girdle, slightly elevating posteriorly along anal-fin base, almost straight along caudal peduncle. Dorsal surface of body covered by plates except for small naked area around dorsalfin base. Ventral surface of head, portion from pelvic-fin insertion to anal-fin origin, and portion around anal-fin totally naked. Abdomen almost completely naked, except for one to four small platelets on each side just posterior to gill opening, sometimes absent in specimens smaller than 50 mm SL.

Head broad and moderately depressed. Dorsal profile of head broadly round in dorsal view; females and juveniles more slender. Interorbital space slightly concave. Three slightly elevated ridges between orbits and snout tip. Lateral ridges from middle of snout to upper margins of orbits more prominent. These ridges ornamented with short hypertrophied odontodes in nuptial males. Lateral margin of head covered with minute odontodes. Snout gently convex in lateral profile; snout tip with ovoid area of naked skin. Nuptial males with well-developed soft fleshy lobes extending along lateral portion of head. Soft fleshy area ornamented with short hypertrophied odontodes, approximately perpendicular to body axis. Eye small, dorsolaterally placed; orbit diameter 8.6-11.3% of head length. Iris operculum small or absent. Nares ovoid, slightly longer than wide, positioned midway between snout tip and anterior orbit margin. Oral disk circular. Lips roundish and well-developed, occupying most of ventral surface of head. Lower lip almost reaching pectoral girdle, densely covered by minute papillae. Papillae surrounded by naked areas, decreasing in size towards edge. Posterior edge slightly fringed. Maxillary barbel short and united to lip by membrane basally, free distally. Both premaxillae and dentaries angled at approximately 120°, with mesial ends slightly curved inwards. Teeth slender, asymmetrically bifid, medial cusp slightly curved inwards. Lateral cusp minute and pointed, never reaching half length of medial cusp.

Dorsal fin originating on vertical line passing through pelvic-fin origin. Dorsal fin short, not reaching preadipose azygous plates when depressed. Nuchal plate exposed, not covered by skin. Dorsal-fin spinelet present but dorsal-fin locking mechanism non-functional. Dorsal-fin spinelet oval and wider than dorsal-fin spine base. Dorsal-fin spine moderately flexible, followed by seven branched rays.Adipose fin with well-ossified leading spine bearing odontodes. Adipose fin preceded by one or two (rarely three) median unpaired preadipose azygous plate. Pectoral fin moderate in size, with curved and depressed spine, covered by minute odontodes in immature males and females. Nuptial males with pectoral fin spine bearing straight and delicate hypertrophied odontodes on outer and ventral faces. Six branched rays, first and second as long as spine. Subsequent branched rays reduced gradually in size. Posterior margin of pectoral fin straight to slightly round, overlapping pelvic-fin origin when adpressed. Pelvic fin with one spine and five branched rays, not reaching or almost reaching to anal-fin origin when adpressed. Pelvic-fin spine depressed, covered with minute odontodes ventrally and laterally; dermal flap on its dorsal surface present and developed, extending to tip of spine. Pelvic-fin flap distinctly higher near fin base. Anal fin with one unbranched and five branched rays; passing adipose-fin origin when adpressed. Caudal-fin forked; lower lobe slightly longer than upper; 14 branched rays. Upper caudal-fin lobe with five and lower lobe with four ventral plate-like procurrent rays, posteriormost elongate. Odontodes on principal and procurrent rays small and irregurlarly arranged.

Coloration in alcohol. Ground color of dorsal surface of head and body grayish or sometimes light brown (dark gray in living specimens), whitish or light yellowish ventrally. Dorsum and flanks mostly plain, neither males nor females with small dark spots or saddles on dorsum and flank. Spines and branched rays of dorsal, anal, and caudal fins plain grayish. Caudal fin sometimes with one or two diffuse narrow bands. Paired fins uniformly grayish, occasionally posterior margin of pectoral fin slightly whitish. Spines of pectoral and pelvic fins uniformly grayish dorsally and ventrally. Fin membranes hyaline. Ventral margin of head, outer portion of upper lip, and ventral portion of caudal peduncle dusky.

Distribution. Pareiorhaphis nasuta is known from three localities in Minas Gerais State, the type-locality in the ribeirão Areia Branca, tributary to the rio Matipó, and two sites in the rio Matipó itself. These sites are located in the upper rio Doce basin and are separated by a maximum of 14 km.

Ecology. The ribeirão Areia Branca, type locality of Pareiorhaphis nasuta , is a small (about three to four meters wide), shallow river with very clear, transparent water, and slow to moderate current. The bottom has rocks, loose stones, and sometimes gravel. Grass or other vegetation is present on the margins. Rapids and small pools were found along the stream, but specimens were captured in areas of rapids among loose stones and pebbles. Nuptial males and larger specimens are usually captured among the larger stones and on the stronger current.

Two other populations were sampled on the main channel of the rio Matipó, at Raul Soares (MCP 38808, ANSP 187153, and MZUFV 2567) in 1997 by Jorge Dergam and at Abre Campo (MCP 38809) in 2002 by F. Vieira. The river was 20 to 25 meters wide, one to two meters deep, and with strong rapids. The water was nearly transparent and slightly black, with fast current. The bottom consisted mostly of large stones and boulders. In this area, the new species was syntopic with Astyanax cf. taeniatus , Hypostomus affinis , Harttia sp. , Neoplecostomus sp. , Trichomycterus spp. , Rhamdia quelen , and Geophagus brasiliensis .

Sexual dimorphism. As usual for Pareiorhaphis (e.g. Reis & Pereira, 1999, fig. 2; Pereira & Reis, 2002, fig. 6; Pereira, 2005, fig. 1), nuptial males of Pareiorhaphis nasuta have a slightly thickened pectoral-fin spine with somewhat enlarged odontodes and hypertrophied odontodes on the lateral margins of head. Odontodes also occur in females and juveniles, but are much smaller. Also, nuptial males of most species are distinguished from females by having a dermal flap on the dorsal surface of the pelvic-fin spine, which is absent or very reduced in females. In addition to that, and contrary to most other Pareiorhaphis species , fully developed males of the P. nasuta have a well-developed fleshy flap along the entire length of the posterodorsal margin of the pectoral-fin spine.

Etymology. The specific epithet of Pareiorhaphis nasuta is from the Latin nasutus, meaning long-nosed, in allusion to the long snout, diagnostic of this species. An adjective.

Figures

Fig. 1. Pareiorhaphis nasuta, holotype, male, MCP 41764, 78.6 mm SL. Brazil: Minas Gerais, ribeirãoAreia Branca, tributary to the upper rio Matipó, rio Doce drainage.