Neoplecostomus pirangaensis, De Oliveira & Oyakawa, 2019

De Oliveira, José C. & Oyakawa, Osvaldo T., 2019, New loricariid fishes from headwaters on Serra da Mantiqueira and Complexo do Espinhaço, Minas Gerais State, Brazil (Teleostei: Siluriformes: Loricariidae), Zootaxa 4586 (3), pp. 401-424 : 412-418

Neoplecostomus pirangaensis , new species

( Figs. 3–7 ; table 3)

Holotype. MZUSP 76340 , male, 77.7 mm SL, Brazil, Minas Gerais State, Rio Doce basin, limit of the municipalities of Carandaí and Senhora dos Remédios, Rio Piranga , 43°42’53”W 20°58’54”S, 794m asl, 31 July 2016, J.C. Oliveira, O.T. Oyakawa, F.M.S.R. Pedro & V.C.M. Souza.

Paratypes. Brazil, Minas Gerais State, upper Rio Doce basin, Rio Piranga basin. MZUSP 76341 , female, 82.7 mm SL, same locality as holotype, 13 Oct 2001, J.C. Oliveira & A.K.G. Lacerda. DZSJRP 21191 , male, 65.8 mm SL, same locality as holotype, 17 September 2000, J.C. Oliveira, E.S. Togoro, A.K.G. Lacerda & A.A. Vidigal. UFJF 1099 , female, 82.7 mm SL, same locality as holotype, 13 Oct 2001, J. C. Oliveira & A.K.G. Lacerda. UFJF 1139 , male, 71.6 mm SL, same locality as holotype, 17 September 2000, J.C. Oliveira, E.S. Togoro, A.K.G. Lacerda & A. A. Vidigal. UFJF 3647 , 5 , 1 male, 76.8 mm SL (c&s), 3 females, 45.9–50.0 mm SL, 1 unsexed, 24.2 mm SL, same data as holotype. DZSJRP 16149 , 3 , unsexed, 26.9–33.8 mm SL, Córrego Cachoeirinha, tributary of the Ribeirão Guarará, Santana dos Montes, 20°48’27”S 43°42’05”W, 779m asl, 4 Sep 2012, F. Langeani & others .

Diagnosis. Neoplecostomus pirangaensis differs from all congeners by the much-reduced dermal platelets on the abdomen, devoid of developed odontodes, between the insertions of the pectoral and pelvic fins (vs. abdomen with conspicuous, small dermal plates between insertions of pectoral and pelvic fins, forming a hexagonal thoracic shield surrounded by naked areas). Neoplecostomus pirangaensis can also be distinguished from all congeners, except N. botucatu and N. paranensis , by the complete absence of vestiges of the adipose fin or azygous plates (vs. vestiges or adipose fin moderate- to well-developed and/or azygous plates present). The new species differs from N. botucatu by the absence of conspicuous dark spots all over the body and the possession of dorsal bands in juveniles, and almost black dorsum in adults. It differs from N. paranensis and N. doceensis by the larger and less numerous teeth (6–9 in premaxilla and 6–10 in dentary, vs. 10–33 and 12–35, respectively). Additionally, the new species differs from the sympatric species, Neoplecostomus doceensis , by the absence of enlarged, fleshy folds between the dentaries. Furthermore, the new species is distinguished from all other species except N. canastra , N. corumba , N. selenae and N. yapo , from the upper Rio Paraná basin, by having a larger orbital diameter (12.0– 13.3% HL, vs. less than 12%).

Description. Morphometric and meristic data in Table 3. Standard length of measured specimens: 33.8–82.7 mm SL. See fig. 3 for general body aspect. Body relatively short and depressed. Greatest width at cleithrum, narrowing posteriorly to caudal peduncle. Dorsal head profile gently convex, elevating from tip of snout to behind of parieto-supraoccipital tip, then horizontally to dorsal-fin origin, then descending to least depth of caudal peduncle. Greatest body depth at pelvic-fin origin. Trunk and caudal peduncle dorsally rounded in cross section; body ventrally flattened to anal-fin origin, then rounded to caudal fin. Dorsal body surface completely covered by plates, except for naked area around dorsal-fin base. Keels along each plate of lateral series absent. First plates of mid-ventral series wider than naked area between them. Snout without plates and odontodes just at its tip. Lateronasal plate absent. Ventral head surface naked except by a plate bearing odontodes in front of gill opening. Canal plate, the only plate on ventral side of head, ventrally to last postrostral plates, simple, not divided. Abdomen with inconspicuous, very small platelets between pectoral- and pelvic-fin insertions, separated from each other by large area of tissue, not forming an abdominal shield, typical for Neoplecostomus ( Fig. 4 ).

Mature males without hypertrophied odontodes and swollen skin along lateral margins of snout and anterodorsal portion of head. Head wide (77.2–91.8% HL) and moderately depressed (45.8–56.3% HL). Head and snout rounded in dorsal view. Interorbital space slightly concave or straight in frontal view. Eye moderately developed (12.0–13.3% HL) and dorsolaterally placed. Lips well developed and rounded; lower lip almost reaching or, more frequently, reaching pectoral girdle; lips covered by papillae distally with smooth area medially and then three rows, with large papillae, just posterior to dentary teeth. Maxillary barbel short and almost entirely joined to lower lip, with free tip. Enlarged fleshy folds between dentaries absent. Teeth large and robust in both females and males ( Fig. 5 ), bicuspid, mesial cusp longer than lateral; premaxilla with 6–9 teeth; dentary with 6–10 teeth.

Dorsal-fin origin posterior to vertical passing through pelvic-fin origin, nuchal plate not covered by skin; dorsal-fin spinelet wider than base of dorsal-fin unbranched thick ray base; dorsal-fin locking mechanism nonfunctional. Dorsal-fin rays II,7; distal margin straight, surpassing vertical through anal-fin origin. Adipose fin absent ( Fig. 6 ). Azygous plates on midline posterior to dorsal fin absent. Pectoral-fin rays I,6, unbranched thick ray depressed and inward curved, more curved in larger specimens and always shorter than longest branched ray; its distal tip soft and, when adpressed, reaching to or just surpassing origin of pelvic fin. Pelvic-fin rays i,5; distal margin soft and, when adpressed, not reaching to anal-fin origin; pelvic-fin unbranched ray thick and ventrally flattened; dermal flap along dorsal surface of first pelvic-fin ray wider in males than in females, and minute flaps only on the two first branched rays of males. Pectoral- and pelvic-fin unbranched ray with odontodes on lateral and ventral portions. Anal-fin rays i,5, posterior margin straight; unbranched ray with odontodes lateroventrally. Caudal-fin rays i,14,i, bifurcate; lower lobe longer than upper.

Color in alcohol. Ground color of dorsal surface of head and trunk dark brown to light brown (in older preserved specimens), almost black in some specimens. Head with pair of parallel pale stripes on naked area of snout tip; pair of pale dots laterally to anterior nasal openings, on interorbital space, and on parieto-supraoccipital, another pair of strips on superior border of opercle. Body dorsal color pattern in some specimens with usual four transverse light bands: first through parieto-supraoccipital, second in middle of dorsal fin, third posterior to dorsal fin, fourth on caudal peduncle at end of anal-fin level. In most specimens, however, banded area largely broken by blackish color, becoming fragmented blotches. Lateral portion of body and ventral portion behind pelvic-fin origin completely dark. Dorsal, pectoral, pelvic, and anal fins dark, with slight, irregular series of lighter bands on rays, and pale borders. Caudal fin dark brown with vertical pale band on its origin and pale tip. Ventral surface of head and trunk pale.

Color in life. Ground color of dorsal surface of head, trunk and fins of freshly collected specimens almost black, with scattered lighter spots in place of usual transverse light brown to yellowish tan bars of other species. Color pattern almost unchanged after one year of preservation in alcohol.

Sexual dimorphism. Males with conspicuous urogenital papilla immediately posterior to anus (vs. absent in females); dermal flap on dorsal surface of the unbranched thick ray and branched pelvic-fin rays, less developed in branched rays (vs. absent in females); females seem to reach a greater length.

Etymology. The specific name pirangaensis is a Latin noun meaning being located or having connection with the Rio Piranga basin, where the species occurs. The Rio Piranga is one of the two rivers that form the Rio Doce itself. The other (Rio do Carmo) has been severely damaged by a disaster with iron ore tailings in November 2015 ( Salinas, 2016; Garcia et al. 2017).

Distribution. Neoplecostomus pirangaensis is known from two localities: in the Rio Piranga, a few kilometers of its headwaters just below of a small hydroelectric power plant, and from the ribeirão Guarará, a left tributary of Rio Piranga, municipality of Santana dos Montes ( Fig. 7 ).

Habitat and ecological notes. Neoplecostomus pirangaensis is sympatric to Neoplecostomus doceensis , in clear waters, with rocky outcrops forming small waterfalls and substrates of rocks and sand. The species is found at the bottom of the rivers among the rocks. The darkness of pigment is also observed in specimens of Neoplecostomus doceensis collect at the same places.

Conservation status. Since 1999, the team of UFJF has made extensive surveys in the upper Rio Piranga and Neoplecostomus pirangaensis was recorded in only two localities with low abundance, the Rio Piranga itself and Ribeirão Guarará. The human activity and potential threat to the species in the region are the same as described to Pareiorhaphis togoroi .

The area of occupancy (AOO) of the species was estimated based on two localities (see above) multiplying by grids of 4 km 2 totaling 8 km 2 (B2). Human activities threaten the habitat welfare (biii) of the only two localities where the species occurs (biv); hence, Neoplecostomus pirangaensis was categorized as an critically endangered (CR) based in the following criteria B2b(iii, iv) according to the International Union for Conservation of Nature (IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2017).

Figures

FIGURE 3. Neoplecostomus pirangaensis, MZUSP 76340, 77.5 mm SL, male, holotype. Brazil, Minas Gerais State, Rio Doce basin. From top to bottom: dorsal, lateral and ventral views.

FIGURE 4. Neoplecostomus pirangaensis, MZUSP 76341, 82.7 mm SL female, paratype, same locality as holotype. Ventral view showing the minute platelets forming a weak abdominal shield surrounded by large naked areas.

FIGURE 5. Neoplecostomus pirangaensis, MZUSP 76340, 77.5 mm SL male, holotype. Close ventral view of oral disk, showing the absence of fleshy folds between dentaries, the size and number of teeth.

FIGURE 6. Neoplecostomus pirangaensis, MZUSP 76341, 82.7 mm SL female, paratype. Close dorsal view of caudal peduncle, showing the complete absence of adipose fin and the azygous plate posterior to dorsal fin.

FIGURE 7. Geographical distribution of Harttia intermontana (star), Pareiorhaphis togoroi (square) and Neoplecostomus pirangaensis (circle). Open symbols = type localities. Red line = boundaries between basins.