Parotocinlus bidentatus, Gauger & Buckup, 2005

Gauger, Marco F. W. & Buckup, Paulo Andreas, 2005, Two new species of Hypoptopomatinae from the rio Paraíba do Sul basin, with comments on the monophyly of Parotocinclus and the Otothyrini (Siluriformes: Loricariidae), Neotropical Ichthyology 3 (4), pp. 509-518 : 512-514

Parotocinlus bidentatus , new species

Fig. 5

Holotype. MNRJ 27962 , 34.8 mm SL, rio Pirapetinga (left bank tributary of rio Paraíba do Sul), Município de Resende (22°28’08"S 44°26’48"W), Rio de Janeiro State, Brazil, G. W. A. Nunan, L. E. M. Cardoso, W. D. Bandeira, 28-30 May 1982 . Paratypes. MNRJ 14217 , 9 , 17.7 - 34.5 mm SL, 1 c& s 32.5 mm SL , AMNH 236543 , 3 , 26.4 - 30.8 mm SL, collected with the holotype ; MNRJ 16011 , 1 , 28.9 mm SL, rio Calçado (right bank tributary of rio Paraíba do Sul), approx. 22°6’S 43°4’W, near highway BR-393, Município de Três Rios , E. P. Caramaschi et al., 23 May 1989 ; MNRJ 17467 , 1 , 29.5 mm SL, rio Pirapetinga, Município de Resende , G. W. Nunan & W. D. Bandeira, 18 Sep 1982 ; MNRJ 28225 , 1 , 34.3 mm SL, rio Barreiro de Baixo (tributary of rio Pirapetinga , Paraíba do Sul basin), 6 Oct 1978 ; MNRJ 28226 , 2 , 26.1 -30.0 mm SL, same locality, G.W. Nunan & W. D. Bandeira, 22 Aug 1982 .

Diagnosis. Parotocinclus bidentatus can be distinguished from all other Hypoptopomatinae except Niobichthys , Epactionotus , Eurycheilichthys , Parotocinclus collinsae , and P. muriaensis by the presence of unicuspid teeth behind the series of bicuspid teeth of the dentary and premaxillary. Parotocinclus bidentatus differs from species of Niobichthys by the absence of thoracic plates; presence of small plates on thorax and abdomen (vs. large plates) and a snout tip plated formed by the rostral plate (vs. snout tip naked). Parotocinclus bidentatus differs from species of Epactionotus by the presence of small plates medially on the abdomen (vs. abdomen naked medially), small interorbital distance entering more than two times in the maximal body width, and a straight head profile (vs. concave). Parotocinclus bidentatus differs from species of Eurycheilichthys by the presence of a single rostral plate at the snout tip (vs. several plates), medial (and lateral) exposure of the ventral surface of the pectoral girdle (vs. ventral exposure restricted to lateral portion of girdle) and six branched rays in the pectoral fin (vs. seven rays). Parotocinclus bidentatus differs from P. collinsae by the absence of an adipose fin and the irregularly distributed small plates on the abdomen (vs. three rows of six plates). Parotocinclus bidentatus differs from P. muriaensis by a small cleithral width (maximum of 27% SL), a proximal and a distal relatively large blotch (vs. small dark dots) on the first two branched rays of the pectoral fin, and complete exposition of the pectoral girdle (vs. partly exposed, Fig. 1 and 2 ).

Additionally the new species can be distinguished from other species of Parotocinclus by the absence of an adipose fin (except for P. muriaensis and occasionally P. spilurus ) and the small number of bicuspid premaxillary (6-12, usually 9) and dentary (4-10, usually 7) teeth (except for P. muriaensis ).

Description. Morphometric and meristic data presented in Table 1. Dorsal profile slightly convex from tip of snout to dorsal-fin origin, straight at dorsal-fin base, straight and parallel to ventral profile of caudal peduncle from end of dorsalfin base to caudal-fin base. Ventral profile from snout to anus straight, transversely flat. Snout tip rounded, rostrum straight. Greatest body depth at dorsal-fin origin 14.7-16.7% SL. Crosssection of body between pectoral and pelvic fins dorsally rounded and ventrally flat; cross-section of caudal peduncle ellipsoid anteriorly, more flattened posteriorly.

Head depressed. Eye 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. Lateral ethmoid exposed posterior to nostril between frontal bone and prefrontal plate, with two rows of odontodes. Enlarged pterotic fenestrae of varied shape and size scattered over surface of pterotic-supracleithrum except for small postero-dorsal edge. Swim bladder capsule with small opening between supraoccipital and pterotic-supracleithrum.

Dorsal fin I,7; its origin slightly posterior to pelvic-fin origin; when depressed reaching beyond vertical line through end of anal-fin base. V-shaped dorsal-fin spinelet present, articulated with roughly hexagonal nuchal plate. Pectoral fin I,6; reaching middle of pelvic-fin length, when depressed. Slit present above pectoral-fin insertion and below lateral process of cleithrum. Pelvic fin i,5; when depressed reaching anal-fin origin in males, reaching beyond anus in females. Dorsal surface of unbranched pelvic-fin ray with skin flap in males. Anal fin i,5. Caudal fin i,7,7,i. Fin notched, ventral caudal-fin lobe slightly longer than dorsal lobe. Total vertebrae 30 (in one c&s specimen).

Lateral line almost complete; pored tubes visible from pterotic-supracleithrum to caudal peduncle; one plate, usually sixth or seventh, without lateral line tube, but canal may continue in skin. Abdomen with numerous small dermal platelets, without naked area. Pectoral girdle entirely exposed ventrally; coracoids entirely covered with odontodes; arrector fossae round, small, not meeting at midline, covered by skin ( Fig. 2 ). Odontodes evenly distributed, regularly arranged on head and body. Enlarged odontodes on anterior and lateral margin of snout, bordering upper lip.

Premaxillary teeth usually 9; dentary teeth usually 7. Accessory unicuspid teeth present internally to main tooth cup in premaxilla and dentary. Oral disk roundish; lower lip covered with papillae; papillae small, except for large papilla located posterior to dentary symphysis; upper lip one third of lower lip; width of lower lip 38.0-53.1% HL, length 23.1-28.5% HL.

Adipose fin represented by two unpaired plates (c&s specimen); some specimens with small elevation at that site which may be less pigmented then surrounding area.

Coloration in alcohol. Coloration better preserved in smaller specimens. Ground color brown to ochre dorsally, yellowish ventrally. Dorsal surface of head from snout tip to pteroticsupracleithrum with darker pigmentation, except for cheeks and triangular clear area extending from snout tip to eyes. Dark pigmentation at dorsal-fin base and unbranched dorsalfin ray; dark triangular blotch extending from proximal onethird of first dorsal-fin ray to base of sixth branched dorsalfin ray; remaining area of fin with small dark spots. Skin near slit at base of pectoral fin with dark chromatophores. First and second branched rays of pectoral fin with two dark patches. Caudal fin with dark trapezoid to triangular area at base extending two-thirds of fin length. One small isolated blotch on dorsal caudal-fin lobe and one on ventral lobe, sometimes continuous with large anterior spot. Anal fin with three large spots along anterior margin.

Distribution. Parotocinclus bidentatus is known from its type locality, at rio Pirapetinga, near Resende, and from rio Calçado, near Três Rios, rio Paraíba do Sul basin, Rio de Janeiro, Brazil ( Fig. 6 ). Based on this limited sample it may be hypothesized that P. bidentatus was originally distributed on the low courses of small tributaries of the rio Paraíba do Sul draining the southeastern slope of the Serra da Mantiqueira and the northern slopes of Serra da Bocaina and Serra dos Órgãos. However, the paucity of specimens in museum collections suggests that the species may have a reduced distribution.

Etymology. The specific epithet P. bidentatus signifies two teeth and is used as a Latin adjective. The name refers to the presence of two types of dentition, namely the usual series of oral teeth and accessory patch of teeth on the upper and lower jaws.

Figures

Fig. 5. Parotocinclus bidentatus, holotype MNRJ 27962, 34.8 mm SL. Brazil: Rio de Janeiro State: rio Pirapetinga (left bank tributary of rio Paraíba do Sul), Resende.

Fig. 1. Ventral view of pectoral girdle of Parotocinclus muriaensis, MNRJ 14753, c&s, 27.3 mm SL. Gray = cleithral roof of arrector fossae.

Fig. 2. Ventral view of pectoral girdle of Parotocinclus bidentatus, MNRJ 14217, c&s, 32.5 mm SL.

Fig. 6. Paraíba do Sul drainage illustrating collecting localities of Parotocinclus bidentatus (circles, type locality on the left) and P. muriaensis (squares). Each symbol may present more than one sample or locality.