Oligosarcus varii, Menezes & Ribeiro, 2015

Menezes, Naércio Aquino & Ribeiro, Alexandre Cunha, 2015, A new species of the lowland Oligosarcus Günther species group (Teleostei: Ostariophysi: Characidae), Neotropical Ichthyology (Neotrop. Ichthyol.) 13 (3), pp. 541-546 : 541-544

Oligosarcus varii , new species

u r n:l sid:z o ob a n k.o r g:a c t: F3691E C0 -C B13- 4F5C -B2A8 - 607DBC1DDF12

Figs. 1-4

Holotype. MCP 31148, female, 184.0 mm SL, Brazil, Rio Grande do Sul, São Marcos, rio Jacuí basin, rio São Marcos near to hydroeletric plant PCH rio São Marcos , 29°02’13”S 51°05’39”W, 13 Sep 2002, A. R. Cardoso & V. A. Bertaco.

Paratypes. MCP 48172, 3 , 175.0-183.0 mm SL, all females, MZUSP 115381, 2 , 181.0-197.0 mm SL, both females, collected with holotype .

Diagnosis. The new species is distinguished from all its congeners by the number of lateral-line scales (56-62 vs. less than 55 or higher than 69), except for Oligosarcus jenynsii (54-65), O. perdido Ribeiro, Cavallaro & Froehlich, 2007 (61-63) and O. jacuiensis (55-65). Oligosarcus varii has in common with O. jenynsii , O. jacuiensis and O. perdido the absence of a foramen on the premaxilla (fig. 2a in Menezes & Ribeiro, 2010) and in this regard differs from O. acutirostris Menezes, 1987 and O. hepsetus ( Cuvier, 1829) in which the foramen is present (fig. 2b in Menezes & Ribeiro, 2010). It can be further distinguished from O. acutirostris in having 21- 24 anal-fin rays (vs. 25-30). Oligosarcus varii differs from O. jenynsii in having the interorbital width 25-26.5% of HL (vs. 18.4-24.4% of HL), the horizontal diameter of the eye 22-23.5% of HL (vs. 25-34% of HL) and the tip of the pectoral fin distant from the vertical through the pelvicfin origin (vs. tip of pectoral fin reaching and extending slightly beyond the vertical through the pelvic-fin origin). Oligosarcus varii differs from O. jacuiensis in having the least interorbital width 25-26.5% of HL (vs. 20-24.5% of HL). Oligosarcus varii differs from O. perdido in having 21-24 longitudinal scale rows around the caudal peduncle (vs. 18-21), 9 longitudinal scale rows from analfin origin to lateral line (vs. 6-8) and 11-12 longitudinal scale rows from dorsal-fin origin to lateral line (vs. 7-11). Oligosarcus varii differs from O. itau Mirande, Aguilera & Azpelicueta, 2011 , O. platensis ( Messner, 1962) and O. amome Almirón, Casciotta, Piálek, Doubnerová & Říčan, 2015 , that have two rows of premaxillary teeth and of pentacuspidate teeth on the dentary.

Description. Morphometrics in Table 1 . Body moderately large, 181-197 mm SL. Head and body profile convex with slight depression at occipital region, concave above caudal peduncle; ventral body profile slightly more convex than dorsal, also concave at lower portion of caudal peduncle. Snout conical, larger than orbital diameter; lower jaw slightly shorter that upper jaw and first two caniniform premaxillary teeth accommodated into two small furrows when mouth is closed. Maxillary widening gradually towards posterior end, its posterior tip not extending beyond vertical crossing posterior edge of orbit; single row of 23-25, 23.8 (24) nearly conical maxillary teeth. Premaxilla with one anterior and one posterior caniniform teeth, and 3 to 4, 3.5 (4) nearly conical teeth aligned with caniniform teeth. Dentary bearing an anterior canine, followed by three conical teeth about equally developed and posterior row of 13-18, 15.1 (13) nearly conical teeth. Ectopterygoid with 12-13, 12.5 (13) nearly conical teeth. All nearly conical teeth on premaxilla, maxilla, dentary and ectopterygoid with vestigial lateral cusps, anterior edge of teeth convex and posterior edge concave, their tips pointing backward. 24-25, 24.3 (24) gill rakers on epibranchial and ceratobranchial portions of first gill arch.

Dorsal-fin origin closer to caudal-fin base than to tip of snout, dorsal-fin rays ii, 9 in all specimens, including holotype. Adipose fin present. Anal-fin rays iv-v,21-24, 22.6 (24), fin origin slightly posterior to vertical crossing base of last dorsal-fin ray. Moderately developed anterior anal-fin lobe including anterior unbranched rays and first 8 or 9 branched rays. Pectoral-fin rays i,11-14, 12.6 (12), tip of longest rays far distant from pelvic-fin origin. Pelvic-fin rays i, 7 in all specimens, including holotype; tip of longest rays reaching anterior border of anus.

Lateral line complete, perforated scales 56-62, 58.5 (59); 11-12, 11.3 (11) horizontal scale rows from dorsalfin origin to lateral line, 9 from anal-fin origin to lateral line in all specimens, including holotype; 21-24, 22.5 (24) horizontal scale rows around caudal peduncle; 24-26, 24.5 (23) scales from tip of occipital to dorsal-fin origin; scale row along both sides of anal-fin base extending to about base of 11 th or 12 th branched anal-fin ray.

ventral portion of opercle darker than dorsal. Dark ovalshaped spot near middle inner border of opercle. Tip of lower jaw dark, this pigmentation extending as a narrow stripe to about half the length of upper lateral portion of lower jaw. Vertically elongate dark humeral blotch wider dorsally and tapering ventrally covering second, third and fourth anterior perforated scales of lateral line. Dark lateral body stripe extending from dorsal portion of opercle across dark humeral blotch to caudal-fin base narrower anterior to caudal peduncle, expanding dorsally and ventrally through posterior portion of caudal peduncle and caudal-fin base and extending over median caudal-fin rays, sometimes obscured by guanine and becoming silvery. All fins pale with scattered dark chromatophores especially on dorsal and caudal fins.

Distribution. Known from the type locality in the rio Jacuí basin in Rio Grande do Sul, Brazil ( Fig. 5 ).

Etymology. Oligosarcus varii is named after Richard P. Vari for his outstanding contribution to the knowledge of South American freshwater fishes.

Color in alcohol. Body pale yellow darker dorsally than ventrally. Dark chromatophores especially concentrated on free edge of scales. Dorsal portion of head and snout darker, dark coloration extending as a narrow stripe over anterior two thirds of maxillary. Lateral head and opercular bones with scattered dark chromatophores, Conservation status. Oligosarcus varii is only known from its type locality, but it probably has a more widely distribution within the Guaíba basin. Threats were not noticed in the area and the species would be classified as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN Standards and Petitons Subcommittee, 2014).

Figures

Fig. 1. Oligosarcus varii, holotype, MCP 31148, female, 184 mm SL, Brazil, Rio Grande do Sul, São Marcos, rio Jacuí basin.

Fig. 2. Horizontal orbital diameter as a function of head length for Oligosarcus varii. Oligosarcus jenynsii and O. jacuiensis introduced for comparisons.

Fig. 3. Least interorbital width as a function of head length for Oligosarcus varii. Oligosarcus jenynsii and O. jacuiensis introduced for comparisons.

Fig. 4. Pectoral-fin length as a function of standard length for Oligosarcus varii. Oligosarcus jenynsii and O. jacuiensis introduced for comparions.

Fig. 5. Rio Jacuí basin showing the collecting site and type locality (red dot) of Oligosarcus varii.