Rhinolekos, Martins & Langeani, 2011

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 : 66

Rhinolekos , new genus

Type species. Rhinolekos britskii , new species.

Diagnosis. Rhinolekos differs from all other Hypoptopomatinae (sensu Schaefer, 1998) (except Microlepidogaster Eigenmann & Eigenmann ) by having the anterior portion of the compound supraneural-first dorsalfin proximal radial contacting the neural spine of the 9 th or 10 th vertebrae ( Fig. 1 ) (vs. 8 th in Epactionotus Reis & Schaefer and 7 th in all other hypoptopomatines). Also, Rhinolekos can be readily distinguished from the remaining Hypoptopomatinae (except Gymnotocinclus anosteos Carvalho, Lehmann & Reis and Acestridium Haseman ) by the presence of the lateronasal plate, a large plate between the second infraorbital plate and the nasal opening, anteriorly projected, surrounding the nostril ( Fig. 2 ). Rhinolekos differs from Gymnotocinclus anosteos by having: dermal plates covering most of the body (vs. extreme reduction of body dermal plates); lateral connecting bone fused to the lateral body plates (vs. absence of lateral connecting bone); bifid hemal spines on caudal vertebrae posterior to first anal-fin proximal radial present (vs. bifid hemal spines absent); all lateral body dermal plates with odontodes posteriorly curved, including the last ones on the caudal peduncle (vs. odontodes on last dermal plates dorsally or anteriorly curved); maxillary barbel reduced, free from lower lip (vs. adnate to lower lip). Furthermore, Rhinolekos differs from Acestridium by having: preopercle emergent to skin surface and visible externally (vs. preopercle not emergent and not visible externally in all Hypoptopomatini taxa, including Acestridium ); head and body relatively wide, not depressed (vs. head and body very slender, depressed); anterior margin of snout markedly rounded, without projection (vs. snout with a conspicuous spatulate projection); dorsal-fin insertion slightly posterior to pelvic-fin base (vs. dorsal fin placed well posterior to pelvic fin and just anterior to anal-fin origin).

Rhinolekos is similar to Microlepidogaster and Pseudotocinclus Nichols , concerning general body shape and may be phylogenetically related with these genera. However, Rhinolekos differs from Microlepidogaster by having ventral surface of pectoral girdle exposed only laterally (vs. totally exposed); arrector fossae partially enclosed, with opening relatively large, extending laterally halfway towards pectoral-fin base (vs. opening reduced). Additionally, Rhinolekos differs from M. perforatus by the absence of the median rostral plate (vs. presence); by presenting the pectoral-fin axillary slit only in juvenile specimens (vs. pectoral-fin axillary slit present, even in adult specimens); paired anterior process of the compound supraneural-first dorsal-fin proximal radial bone absent (vs. present, linking the supraneural with the supraoccipital via ligament); median plate series continuous to the caudal-fin origin (vs. median plate series truncated, ending before the caudal-fin base), and iris operculum present (vs. absent). Finally, Rhinolekos differs from Pseudotocinclus by having the caudal peduncle roughly rounded in cross section (vs. caudal peduncle distinctly square in cross section); longitudinal crests in supraoccipital absent (vs. present); fourth infraorbital expanded ventrally (vs. not expanded).

Distribution. Rhinolekos is restricted to streams of the rio Paranaíba drainage, Goiás State, central Brazil ( Fig. 3 ).

Etymology. The generic name is a combination of the greek, rhinos = nose, nostril and lekos = plate, in reference to presence of the lateronasal plate. Gender masculine.

Key to species of Rhinolekos

1. Premaxillary and dentary accessory teeth present; caudal peduncle shallow (7.7-8.7% of SL); 18-20 (mode 19) middorsal plates........................................ Rhinolekos schaeferi

1’. Premaxillary and dentary accessory teeth absent; caudalpeduncle deep (greater than 9.0% of SL); 21-27 (mode 22 in R. britskii and 24 or 25 in R. garavelloi ) mid-dorsal plates........................................................................................2

2. Transverse dark band in pectoral, pelvic and anal-fin rays present; thoracic length 14.7-18.0% SL; 24-28 dorsal plates....................................................... Rhinolekos britskii

2’. Transverse dark band in pectoral, pelvic and anal-fin rays absent; thoracic length 18.1-20.8% SL; 30-35 dorsal plates................................................ Rhinolekos garavelloi

Figures

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. 2. Skull of Rhinolekos schaeferi (left side, dorsal view), paratype, DZSJRP 12192, 36.5 mm SL. Scale bar = 1 mm. CP1- 2 = cheek plates; F = frontal; IO1-5 = infraorbitals 1-5; LE = lateral ethmoid; LNP = lateronasal plate; N = nasal; NP = nuchal plate; OP = opercle; PF = prefontral plate; POP = preopercle; PR1-3 = postrostrals plates 1-3; PT-SC = compound pterotic; SOC = supraoccipital; SPH = sphenotic.

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.