Scleronema milonga, Ferrer & Malabarba, 2020

Ferrer, Juliano & Malabarba, Luiz R., 2020, Systematic revision of the Neotropical catfish genus Scleronema (Siluriformes: Trichomycteridae), with descriptions of six new species from Pampa grasslands, Neotropical Ichthyology (e 190081) 18 (2), pp. 1-81 : 34-40

Scleronema milonga , new species urn:lsid:zoobank.org:act:5F928D71-F119-4D49-A407-465C21CE08CA

( Figs. 1B , 5C , 14-15 ; Tabs. 3, 7)

Scleronema operculatum [non Eigenmann, 1917] —Adriaens et al., 2010: 339 (specimen used for CT-scanning), 349; fig. 5C (CT-scanning from lateral view of head, pectoral fin, and anterior portion of axial skeleton).

Scleronema sp. n. 1 —Bertaco et al., 2016: 421 (listed). —Ferrer, 2016: 95–100; figs. 47–50 (phylogenetic relationships, taxonomy).

Scleronema aff. minutum —Carvalho, 2017: 20 (diet, ecomorphology and reproduction).

Scleronema sp. —Cavalheiro, Fialho, 2020: 7 (listed).

Holotype. MCP 54165 , 37.8 mm SL, Brazil, Rio Grande do Sul, Dezesseis de Novembro, arroio Lageado Araçá, rio Ijuí basin, lower rio Uruguay, 28º12’23”S 54º56’58”W, 1 Nov 2004, A. R. Cardoso & V. A. Bertaco.

Paratypes. 43 specimens from lower rio Uruguay. Argentina, Misiones : MCP 13354 *, 3, 28.8–30.7 mm SL, Itacaruaré , arroyo Itacaruaré , 27°53’S 55°17’W, 28 Jun 1989, E. Lerner. MCP 13445 *, 1, 17.5 mm SL, Itacaruaré , arroyo Itacaruaré , 27°53’S 55°17’W, 24 Abr 1989, E. Lerner et al. Brazil, all from rio Ijuí basin: LIRP 16775 *, 5, 25.7–35.3 mm SL, Panambi , rio Palmeira , 28°14’35”S 53°33’12”W, 8 Fev 2014, A. Hirschmann & C. B. Kasper. MCP 16768 *, 2, 25.3–33.8 mm SL, Entre-Ijuís , arroio Lageado do Moinho , rio Ijuizinho basin, 28°27’S 54°22’W, 14 Dez 1993, J. F. P. Silva, M. P. Barros & R. E. Reis. MCP 35344 *, 7, 21.3–39.2 mm SL, Cerro Largo, arroio Brum, 28º11’10”S 54º49’36”W, 12 Jun 2004, A. R. Cardoso & V. A. Bertaco. MCP 37034 *, 4 (1 c&s), 32.9–36.4 mm SL, Salvador das Missões, arroio Alexandrino, 28º10’25”S 54º48’05”W, 31 Out 2004, A. R. Cardoso & V. A. Bertaco. MCP 37052 *, 5, 25.8–33.9 mm SL, collected with holotype. UFRGS 7685 *, 4, 19.5–32.7 mm SL, São Nicolau, unnamed stream tributary of rio Ijuí , 28°10’32”S 55°04’01”W, 5 Mar 2005, C. Oliveira, J. Ferrer, L. R. Malabarba, M. A. Azevedo. UFRGS 11706 *, 3 (2 c&s), 29.2–33.5 mm SL, Panambi, rio Divisa , 28°13’13”S 53°33’46”W, 19 Out 2009, A. Hirschmann & C. B. Kasper. UFRGS 14621 , 4 , 18.4–21.5 mm SL, Pirapó, rio Ijuí-Mirim near mouth wih rio Ijuí , 28°02’53”S 55°10’59”W, 5 Mar 2005, C. Oliveira, J. Ferrer, L. R. Malabarba, M. A. Azevedo. UFRGS 15287 , 1 , 34.3 mm SL, Panambi, rio Palmeira, 28°14’35”S 53°33’12”W, 24 Jun 2011, A. Hirschmann & C. B. Kasper. UFRGS 19104 , 4 , 19.8–32.3 mm SL, Panambi, rio Palmeira, 28°14’35”S 53°33’12”W, 8 Fev 2014, A. Hirschmann & C. B. Kasper .

Diagnosis. Scleronema milonga is distinguished from all congeners, with the exception of S. ibirapuita and S. teiniagua , by the absence of the pore s3 of the supraorbital line of the laterosensory system (vs. pore s3 present). Scleronema milonga differs from S. ibirapuita and S. teiniagua by the presence of the pore s6 of the supraorbital line of the laterosensory system (vs. pore s6 absent). Additionally, Scleronema milonga is distinguished from S. mate and S. guapa by having the rounded brown blotches at the midlateral line larger than opercle (vs. rounded brown blotches as large as or smaller than opercle in S. mate and absent in S. guapa ).

Description. Based on specimens ranging from 17.5 to 39.2 mm SL; 3 c&s (one dissected). Morphometric data for 35 types in Tab. 7.

External morphology. Greatest height and width of body in half-length of trunk. Body elongate, trunk roughly cylindrical gradually compressed towards to caudal fin.

Dorsal profile of trunk convex and ventral profile straight to slightly convex. Dorsal and ventral profiles of caudal peduncle straight. Dorsal margin of caudal peduncle with thin membrane, resembling adipose fin ( Fig. 1 ). Head depressed and wide, trapezoid-shaped from dorsal view, wider posteriorly. Dorsal and ventral profiles of head straight. Anterior snout profile usually rounded from dorsal view. Nostrils of equivalent size, smaller than eye diameter. Anterior nostril surrounded by fleshy flap of integument, posterolaterally continuous with nasal barbel. Posterior nostril surrounded anterolaterally by thin flap of integument. Eyes rounded, dorsally oriented but also visible from lateral view; located behind posterior nostrils; orbital rim not free; eyes covered by thin and transparent skin.

Barbels with large bases and tapering gradually towards tips. Nasal barbel long;

emerging from posterolateral edge of anterior nostril extending between anterior and posterior margins of eye. Maxillary barbel long; emerging from edge of upper lip and extending between anterior and posterior margins of interopercle. Basal portion of maxillary barbel wide with thin fleshy flap dorsally and distal margin rounded. Maxillary barbel with thinner portion longer in length than wider one. Rictal barbel emerging from lateral lobe of lower lip and slightly shorter than maxillary barbel. Mouth subterminal with edges posteriorly oriented. Upper lip wider than lower lip. Lower lip with round fleshy lobes in corners. Ventral surface of lower lip with small papillae. Gill openings not constricted united with isthmus anteriorly forming free fold. Opercular patch of odontodes rounded, inserted in posterior region of head visible from dorsal and lateral views. Posterior margin of opercle with distinct skin flap short and rounded. Interopercular patch of odontodes elongate inserted on posteroventral region of head visible from lateral and ventral views. Odontodes of opercle and interopercle barely visible, completely involved by flesh.

Pectoral fin with distal margin convex when expanded, 7(n = 44; including holotype) rays; first one always unbranched and not prolonged as filament; fourth and fifth longest. Pectoral-fin insertion posterior to branchial aperture usually covered by branchial membrane anteriorly. Some specimens with intumescence above anterior portion of pectoral fin and axillary pore visible. Pelvic fin with distal margin convex when expanded, 4/5(n = 1) or 5(n = 43; including holotype) rays; first one always unbranched. Pelvic-fin origin located at vertical through dorsal-fin origin or briefly anterior extending between urogenital papilla and anal-fin anterior insertion; tangentially inserted with inner margins separated by large interspace. Urogenital papilla located between last third of pelvic fins.

Dorsal fin with distal margin straight to slightly convex when expanded, 9(n = 18), or 10(n = 26; including holotype) rays; usually first two rays unbranched. Dorsal fin with 2(n = 2) procurrent rays. Dorsal-fin origin located at vertical through origin of pelvic fin or briefly posterior. Anal fin with distal margin slightly convex when expanded, 6(n = 40; including holotype) or 7(n = 4); usually first two rays unbranched. Anal fin with 2(n = 2) procurrent rays. Anal-fin origin located at vertical through last third of dorsal-fin base. Caudal fin with distal margin straight and corners slightly rounded, 10(n = 1), 11(n = 1) or 12(n = 42; including holotype) rays; most-external rays of dorsal and ventral plates of caudal fin always unbranched and smaller than branched rays. Branched rays of caudal fin splitting up to twice. Caudal fin with 10(n = 1) or 13(n = 1) procurrent rays dorsally and 10(n = 1) or 11(n = 1) procurrent rays ventrally. Procurrent rays of dorsal, anal, and caudal fins rarely visible.

Osteology. Premaxilla with teeth arranged in three rows. Dentary with 21–27(n = 2). Opercle with 12–16(n = 2) odontodes and interopercle with 14–16(n = 2) odontodes. Hyoid arch with 6(n = 2) branchiostegal rays. Free vertebrae 34(n = 2) or 35(n = 1); abdominal vertebrae 3(n = 2) or 5(n = 1). Ribs 9(n = 2) or 11(n = 1). First complete haemal arch in 4 th (n = 2) or 6 th (n = 1) free vertebra, first haemal spine in 11 th (n = 2) or 12 th (n = 1) free vertebra. Dorsal fin with 9(n = 1) or 10(n = 2) pterygiophores; first one inserted anteriorly to neural spine of 14 th (n = 3) vertebra. Anal fin 6(n = 3) pterygiophores; first one inserted anteriorly to haemal spine of 18 th (n = 1) or 19 th (n = 2) vertebra.

Laterosensory system. Data for 44 specimens summarized in Tab. 3. Canals of laterosensory system with simple (non-dendritic) tubes and external pores. Supraorbital line with nasal canal and pore s3 of frontal canal invariably absent; pore s6 of frontal canal usually present ( Fig. 5C ). Infraorbital line with antorbital segment invariably absent and sphenotic canal with pores i10 and i11. Posterior segment of frontal, sphenotic and otic canals fused each other. Otic, posotic and scapular canals present with preoperculo-mandibular and pterotic branches short and usually with one pore each (po1 and po2, respectively). Trunk canal short usually with two pores.

Coloration in alcohol. Lateral surface of body with midlateral line of 6–8 rounded black blotches larger than opercle over light yellow background; blotches of some individuals becoming fade or absent towards caudal peduncle ( Figs. 14–15 ). Some individuals with lateral blotches in contact, almost forming continuous stripe (LIRP 16775). Dorsal surface of body with 5–6 rectangular black blotches extending ventrally to laterodorsal surface of body. Anterior portion of opercle black. Ventral surface of body light yellow with few brown blotches in caudal peduncle. Dorsal and laterodorsal surfaces of head with numerous brown rounded blotches over light yellow background. Ventral surface of head light yellow with few small brown blotches in lower lip, sometimes forming thin stripe. Barbels uniformly yellow or intercalated with brown areas. Pectoral-, pelvic-, and anal-fin rays faintly brown. Dorsal and caudal fins with vertical light brown stripe basally, rays faintly brown, and distal margins hyaline ( Figs. 14–15 ).

Coloration in life. Coloration in life similar to that of specimens preserved in ethyl alcohol, but more intense and with midlateral blotches of body brown ( Fig. 15 ).

Geographical distribution. Scleronema milonga occurs in the rio Ijuí and rio Santa

Rosa basins, two tributaries to the left bank of rio Uruguay, southern Brazil; and small tributaries of the right bank of the rio Uruguay, Misiones, Argentina ( Fig. 4 ).

Ecological notes. Scleronema milonga inhabits rivers and streams with sand- and gravel-bottoms. The species has not been collected syntopically with its congeners.

Individuals of S. milonga larger than 31.0 mm SL are capable to spawn and considered adults by Carvalho (2017). Its diet is composed mainly of immature, autochthonous and benthic insects (Ephemeroptera, Chironomidae , and Trichoptera), in both adults and immatures (Carvalho, 2017).

Etymology. The species epithet “milonga ” is given in reference to the musical rhythm popularized in Argentina and Rio Grande do Sul State ( Brazil), both regions where the new species can be found. A noun in apposition.

Conservation status. Scleronema milonga has an Extent of Occurrence (EOO) less than 5,000 km 2 and a significant part of the original vegetation of the rio Ijuí basin in Brazil was converted to soybean crops. However, no additional threats were detected and the species occurs in well-preserved areas of Argentina. Thus, the species can be classified as Least Concern (LC) according to IUCN criteria (IUCN, 2019).

Additional material examined. MCP 13442, 1, 16.3 mm SL, Argentina, Misiones, Itacaruaré, arroyo Santa Maria, lower río Uruguay. UFRGS 27844, 8, 25.9–34.6 mm SL, Brazil, Santa Rosa, rio Santa Rosa at the confluence with a stream, lower rio Uruguay.

Figures

FIGURE 1 | Lateral view of A. Scleronema macanuda, new species, paratype (ZVC-P 9374; 74.5 mm SL) and B. S. milonga, new species, holotype (MCP 54165; 37.8 mm SL) showing the thick fleshy flap in the base of the maxillary barbel (red arrows), the skin flap in the posterior margin of the opercle (black arrows), the dorsal membrane in the caudal peduncle (white arrows), and the vertical black bar in the caudal fin (blue arrow).

FIGURE 4 | Geographical distribution of the genus Scleronema. Circles and squares indicate species of the S. minutum group and S. operculatum group, respectively. Some symbols represent more than one collection locality. AR = Argentina; BR = Brazil; PY = Paraguay; UY = Uruguay.

FIGURE 5 | Dorsal view of the head of A. Scleronema mate, new species, paratype (UFRGS 17418; 34.9 mm SL), B. S. ibirapuita, new species, paratype (UFRGS 27402; 49.4 mm SL), C. S. milonga, new species, paratype (LIRP 16775; 35.3 mm SL), and D. S. minutum (UFRGS 19651; 46.4 mm SL) showing the pores of the laterosensory system. “Ap” = additional pore.

FIGURE 14 | Scleronema milonga, new species, holotype (MCP 54165; 37.8 mm SL), Brazil, Rio Grande do Sul, Dezesseis de Novembro, arroio Lageado Araçá, rio Ijuí drainage, lower rio Uruguay.

FIGURE 15 | Specimen just after the fixation in formalin of Scleronema milonga, new species, paratype (UFRGS 7685; 32.7 mm SL), Brazil, Rio Grande do Sul, São Nicolau, unnamed stream tributary to rio Ijuí, lower rio Uruguay.