Rhinolekos britskii Martins, Langeani

Martins, Fernanda de Oliveira & Langeani, Francisco, 2011, Rhinolekos, a new genus with three new species of Hypoptopomatinae (Siluriformes: Loricariidae) from upper rio Paraná, Neotropical Ichthyology 9 (1), pp. 65-78 : 68-70

Rhinolekos britskii Martins, Langeani & Costa, new species

Fig. 4

Holotype. DZSJRP 6489 , 32.2 mm SL, female, Brazil, Goiás State, Bela Vista de Goiás, tributary of the córrego Arapuca, Fazenda Arapuca , rio Paranaíba drainage, 17º04’06”S 48º43’59”W, 29 Apr 2004, F. Langeani & D. O. Tavares.

Paratypes. All from Brazil, Goiás State, rio Paranaíba drainage . DZSJRP 12190 , 17 , 1 c&s, 21.8-35.5 mm SL (7, 31.9-35.5 mm SL), collected with holotype ; DZSJRP 5567 , 1 , 19.7 mm SL, Bela Vista de Goiás, córrego Arapuca , dirt road of GO-020 (BR-352), 17º06’16”S 48º43’08”W, 22 May 2003, F. Langeani, J. P. Serra, F . R. Carvalho & D. O. Tavares ; DZSJRP 5604 , 1 , 18.4 mm SL , DZSJRP 5608 , 1 , 36.5 mm SL, Cristianópolis, córrego Gameleira , GO-020 (BR-352) 17º10’19”S 48º43’36”W, 22 May 2003, F. Langeani, J. P. Serra, F . R. Carvalho & D. O. Tavares ; DZSJRP 5614 , 6 , 14.3-34.4 mm SL (2, 33.6-34.4 mm SL), Bela Vista de Goiás, córrego Campo Alegre , 17º09’09”S 48º44’00”W, 22 May 2003, J. P. Serra, F. Langeani, F . R. Carvalho & D. O. Tavares ; DZSJRP 6514 , 2 , 23.7-35.6 mm SL (1, 35.6 mm SL), Bela Vista de Goiás, córrego dos Macacos, Fazenda Arapuca Velha , 17º05’26”S 48º44’04”W, 29 Apr 2004, F. Langeani & D. O. Tavares ; DZSJRP 6884 , 7 , 2 c&s, 22.2-38.2 mm SL (6, 30.7-38.2 mm SL) . MZUSP 103698 , 6 , 26.7-36.3 mm SL (3, 30.7-36.3 mm SL), Bela Vista de Goiás, Corumbá tributary, Fazenda Arapuca , far away 25 km from GO-020, 17º04’08”S, 48º43’59”W, 25 Jul 2004, D. O. Tavares, G. A. Tavares & D. J. Correa Jr .; DZSJRP 6983 , 7 , 1 c&s, 16.8-40.0 mm SL, Bela Vista de Goiás, córrego dos Macacos, rio Corumbá , GO-020, Km 78, 17º04’39”S 48º43’20”W, 1 Nov 2004, D. O. Tavares, G. A. Tavares & D. J. Correa Jr .; DZSJRP 7018 , 12 , 1 c&s, 15.0- 33.5 mm SL, (1, 33.5 mm SL) , DZSJRP 7022 , 1 c&s, 31.2 mm SL , MCP 44058, 5 , 22.2 -36.0 mm SL (2, 32.4-36.0 mm SL) , MNRJ 34128 , 5 , 26.1-35.5 mm SL (3, 31.1-35.5 mm SL), Bela Vista de Goiás, rio Corumbá tributary, GO-020, Km 78, 17º04’08”S 48º44’01”W, 1 Nov 2004, D. O. Tavares, G. A. Tavares & D. J. Correa Jr .; DZSJRP 7036 , 2 , 37.3 -38.0 mm SL (1, 38.0 mm SL), Bela Vista de Goiás, córrego dos Macacos, rio Corumbá , GO-020, Km 78, 17º04’38”S 48º43’18”W, 6 Feb 2005, G. A Tavares, D. J. Correa Jr. & W. C. Carmo ; DZSJRP 7042 , 6 , 19.3-35.3 mm SL (1, 35.3 mm SL), Bela Vista de Goiás, rio Corumbá tributary, GO-020, Km 78, 17º04’07”S 48º43’59”W, 6 Feb 2005, G. A Tavares, D. J. Correa Jr. & W. C. Carmo ; DZSJRP 7045 , 3 , 34.6-37.5 mm SL, Bela Vista de Goiás, rio Corumbá tributary, GO-020, Km 78, 17º05’27”S 48º44’40”W, 6 Feb 2005, G. A. Tavares, D. J. Correa Jr. & W. C. Carmo .

Diagnosis. Rhinolekos britskii differs from its congeners by the following characters: transverse dark bands in pectoral-, pelvic- and anal-fin rays present (vs. absent); 31 vertebrae (vs. 32), and by anterior portion of the compound supraneuralfirst dorsal-fin proximal radial contacting the neural spine of the 9 th vertebra (vs. 10 th). Furthermore, R. britskii could be distinguished from R. garavelloi by the larger postanal length (34.7-37.7% in SL vs. 29.0-34.6%); smaller thoracic length (14.7- 18.0% in SL vs. 18.1-20.8%); and fewer plates in the dorsal series (24-28 vs. 30-35). It differs from R. schaeferi by the absence of premaxillary and dentary accessory teeth (vs. presence); and 21-24 mid-dorsal plates (vs. 18-20).

Description. Morphometric and meristic data are given in Tables 1 and 2. Dorsal body profile convex from tip of snout to dorsal-fin origin; concave at dorsal-fin base; almost straight to caudal-fin origin. Small elevation at supraoccipital immediately posterior to eyes. Ventral head profile slightly concave. Ventral body profile almost straight from pectoralfin origin to anal-fin origin, ascending at anal-fin base. Greatest body depth at dorsal-fin origin. Greatest body width at opercular region, gradually tapering towards snout and caudal fin. Head without longitudinal crests, anterior margin rounded in dorsal view. Snout without rostral plate, bearing numerous small plates with thin odontodes; most anterior portion of head naked. Odontodes equal in size and uniformly distributed, not forming rows, on head and body. Eye small, dorsolaterally placed, not visible from ventral view. Iris operculum present, very reduced in some specimens. Infraorbital canal entering infraorbital series via compound pterotic. Compound pterotic roughly quadrangular in shape, without elongate posterior extension, its posteroventral margin with irregular and median to large perforations. Supraoccipital not contributing to the dorsal portion of the swimbladder capsule.

Body entirely covered with bony plates, except on ventral part of head, region overlying opening of swim bladder capsule, and around anus and pelvic-fin origin. Abdomen covered with small plates irregularly arranged.

Lips roundish, papillose; lower lip larger than upper lip, with papillae gradually smaller towards edges. Maxillary barbel free from lower lip and reduced. Teeth slender, bifid; median cusp larger and rounded, lateral cusp smaller and pointed. Premaxillary teeth 19-28. Dentary teeth 18-25. Number of teeth increasing with size. Premaxillary and dentary accessory teeth absent.

Dorsal-fin rays ii,6-7, originating approximately at vertical through middle of pelvic fin; its length surpassing anal-fin origin; spinelet small, approximately rectangular, posterior margin slightly convex; locking mechanism non-functional. Anterior portion of compound supraneural-first dorsal-fin proximal radial contacting neural spine of 9 th vertebra ( Fig. 1a ). Pectoral-fin rays i,6, originating immediately posterior to opercular opening and surpassing pelvic-fin origin. Cleithrum and coracoid exposed and supporting odontodes only laterally, near pectoral-fin insertion. Arrector fossae partially enclosed by ventral lamina of coracoid; opening relatively large, extending laterally halfway towards pectoralfin base. Pectoral-fin axillary slit present only in juvenile specimens. Pelvic-fin rays i,5, reaching anal-fin origin when depressed. Pectoral- and pelvic-fin unbranched ray shorter than branched rays; enlarged odontodes at tip of pectoralfin unbranched ray and at mesial margin of pelvic-fin unbranched ray. Anal-fin rays i,5. Caudal-fin rays i,14,i, lower lobe slightly longer than upper lobe; four or five dorsal and four ventral procurrent rays. Adipose fin absent; replaced by single azygous plate in some specimens. Median lateral plates 26-30. Median-plate series complete, from compound pterotic to caudal-fin base, absence of canal in one plate near region of tenth median plate in some specimens. Vertebrae 31.

Color in alcohol. Ground color of dorsal surface brown. Trunk with four transverse dark bars: first at dorsal-fin origin, triangular in some specimens; second, ventral to dorsal-fin rays; third at vertical through middle of anal fin; last near caudal-fin insertion. Light brown area between tip of snout and nares. Opercle region unpigmented. Lateral portion of body brown, with dark longitudinal stripe, from compound pterotic to caudal-fin origin. Ventral surface of body mostly unpigmented. Dorsal-, anal-, pectoral-, and pelvic-fins membranes hyaline, with transverse dark bands along rays. Caudal fin densely pigmented, tip of lobes hyaline; some specimens, mainly juveniles, with a circular unpigmented area on each lobe. Procurrent rays sometimes with yellowish white coloration, extending laterally to caudal peduncle.

Sexual dimorphism. Males with conspicuous urogenital papillae immediately posterior to anus, and with a dorsal expanded flap of skin in all pelvic-fin rays.

Distribution. Streams from rio Paranaíba drainage, upper rio Paraná system, Goiás State, Brazil ( Fig. 3 ).

Etymology. Named after Heraldo A. Britski, Museu de Zoologia da Universidade de São Paulo, in recognition of his dedication and remarkable contributions to the studies in Hypoptopomatinae and to Neotropical Ichthyology, in general.

Remarks. Filipi Cezaro Costa contributed to the description of Rhinolekos britskii and is therefore included as one of the authors of this species.

Figures

Fig. 4. Rhinolekos britskii, holotype, DZSJRP 6489, 32.2 mm SL, female, tributary of the córrego Arapuca, rio Paranaíba drainage, Bela Vista de Goiás, Goiás State, Brazil.

Fig. 1. Anterior portion of axial skeleton and dorsal-fin supports (left side, lateral view). a) Rhinolekos britskii, DZSJRP 6489, 28.0 mm SL. b) Rhinolekos garavelloi, DZSJRP 10477, 30.4 mm SL. c) Rhinolekos schaeferi, DZSJRP 12192, 36.5 mm SL. Scale bar = 1 mm. Vertebrae counts included five from the Weberian apparatus. RV6 = rib of sixth vertebra; PX2-3 = compound proximal and medial radial 2-3; SN+PX1 = compound supraneural first dorsal-fin proximal radial; SP1 = first dorsal-fin spinelet; SP2 = second dorsal-fin spine; V6-12 = vertebrae 6-12.

Fig. 3. Southeastern Brazil showing type locality of the Rhinolekos species (1 - rio Corumbá; 2 - rio Paranaíba; 3 - rio Grande; 4 - rio Paraná). Circle - R. britskii; Square - R. garavelloi; Star - R. schaeferi.