Parotocinclus muriaensis, 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 : 514-516

Parotocinclus muriaensis , new species Fig. 7

Holotype. MNRJ 28528 , 31.0 mm SL, rio Muriaé river (left bank tributary of rio Paraíba do Sul), near intersection of highways BR-356 and RJ- 186, 20 km downstream from Itaperuna, approx. 21°15" S 41°45 "W, Município de Itaperuna, Rio de Janeiro State, Brazil, D. F. Moraes Jr. et al., 24 Oct 1989.

Paratypes. MNRJ 14753 , 3 , 26.1 - 28.8 mm SL, 1 c&s, 27.3 mm SL, 1 with deformed snout, collected with the holotype .

Diagnosis. Parotocinclus muriaensis can be distinguished from all other Hypoptopomatinae except Niobichthys , Epactionotus , Eurycheilichthys , Parotocinclus collinsae , and P. bidentatus by the presence of unicuspid teeth behind the series of bicuspid teeth of the dentary and premaxillary. Parotocinclus muriaensis differs from species of Niobichthys by the absence of thoracic plates; the presence of small plates on the thorax and abdomen (vs. large plates) and a plated snout tip formed by the rostral plate (vs. naked snout tip). Parotocinclus muriaensis differs from species of Epactionotus by the presence of small plates medially on the abdomen (vs. abdomen naked medially), a small interorbital distance entering more than two times in the maximal body width, and a straight head profile (vs. concave). Parotocinclus muriaensis 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 muriaensis differs from P. collinsae by the absence of the adipose fin, and the irregularly distributed small plates on the abdomen (vs. three rows of six plates). Parotocinclus muriaensis differs from P. bidentatus by a large cleithral width (minimum of 28% SL), presence of small dark dots on the first two branched rays of the pectoral fin (vs. a proximal and a distal relatively large blotch on the first two branched rays), and a medially naked area on the pectoral girdle ( Fig. 1 ).

Additionally the new species can be distinguished from other species of Parotocinclus by the absence of the adipose fin (except for P. bidentatus and occasionally P. spilurus ), and the small number of bicuspid premaxillary (10-12, usually 10- 11) and dentary (7-8, usually 8) teeth (except for P. bidentatus ).

Description. Morphometric and meristic data presented in Table 2. Dorsal profile slightly convex to straight from snout tip to dorsal-fin origin, straight at dorsal-fin base, straight and parallel to ventral profile of caudal peduncle from end of dorsal-fin 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, 15.8-17.4% 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. 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. Presence of an opening between supraoccipital and pterotic-supracleithrum, where third bony structure emerges on surface of cranium. 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 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 vertebra 28 (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 plates. Median portion of pectoral girdle not exposed ventrally; arrector fossae ellipsoid, large (length of pectoral girdle), meeting at midline, covered by skin ( Fig. 1 ). Odontodes evenly distributed, regularly arranged on head and body. Enlarged odontodes on anterior and lateral margins of snout, bordering upper lip.

Premaxillary teeth usually 10-11; dentary teeth usually 8. Accessory unicuspid teeth present internally to 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 45.2-53.8% HL, length 20.5-27.6% HL.

Adipose fin represented by unpaired plate (c&s specimen); in some specimens small elevation at that site which may be less pigmented than surrounding area.

Coloration in alcohol. Coloration better preserved in smaller specimens. Ground color brown to ochre dorsally, yellowish ventrally. Pigmentation darker on dorsal surface of head between nostrils and pterotic-supracleithra, base of dorsal fin, skin surrounding slit at base of pectoral fin. Fin rays with regularly distributed brownish dots. Large dark, nearly trapezoid area at caudal-fin base extending posteriorly one-third of caudal-fin length; irregular, isolated dark blotch at tips of upper and lower caudal-fin lobes; horizontal black line sometimes present near middle caudal-fin rays.

Distribution. Parotocinclus muriaensis is known only from its type locality, at rio Muriaé near Itaperuna, a left tributary of the rio Paraiba do Sul basin, Rio de Janeiro, Brazil ( Fig. 6 ).

Etymology. The specific epithet refers to the rio Muriaé, where this new species was collected.

Unidentified specimens. Two specimens (MNRJ 16048, 26.0- 28.9 mm SL) from córrego da Areia in the county of Chiador are similar to the two new species described above. They differ by the smaller cleithral width (23.9 and 25.8% SL vs. 28.1-29.2% SL in P. muriaense , 24.7-26.4% SL in P. bidentatus ) and head depth (34.1 and 39.2% HL vs. 43.4-44.0% HL in P. muriaense , 39.9-47.5% HL in P. bidentatus ), and the lower lip is wider than in P. bidentatus (29.4 and 32.5% HL vs. 23.1- 27.3% HL). The two specimens are more similar to P.bidentatus than to P. muriaensis . However, due to their small size, we cannot ascertain whether they represent a third species or simply a local variation of one of the described species.

Figures

Fig. 7. Parotocinclus muriaensis, holotype MNRJ 28528, 31.0 mm SL. Brazil: Rio de Janeiro State: rio Muriaé river (left bank tributary of rio Paraíba do Sul), near intersection of highways BR-356 and RJ-186, 20 km downstream from Itaperuna, Município de Itaperuna.

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. 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.