Scleronema ibirapuita, 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 : 17-21

Scleronema ibirapuita , new species urn:lsid:zoobank.org:act:CBB4C41B-EEC8-4CDE-81DC-C99D4D4E2E1B

( Figs. 5B , 8 ; Tabs. 3–4)

Scleronema sp. —Bertaco, Azevedo, 2013: 969 (listed).

Scleronema sp. n. 2 —Bertaco et al., 2016: 421 (listed). —Ferrer, 2016: 90–94; figs. 47–50 (phylogenetic relationships, taxonomy).

Holotype. MCN 19470, 39.5 mm SL, Brazil, Rio Grande do Sul State, Santana do Livramento, “Área de Proteção Ambiental Ibirapuitã” Conservation Unit, rio Ibirapuitã Chico , tributary of rio Ibirapuitã , rio Ibicuí basin, lower rio Uruguay, 30º33’29”S 55º31’03”W, 28 Aug 2012, C. L. Castilho, M. A. Azevedo & V. A. Bertaco.

Paratypes. 45 specimens from Brazil, Rio Grande do Sul State, rio Ibirapuitã basin, rio Ibicuí basin, lower rio Uruguay: MCP 11171 *, 6 (1 c&s), 28.3–39.4 mm SL, Rosário do Sul , unnamed stream tributary of rio Ibirapuitã , 30º11’S 55º39’W, 13 Nov 1986, C. Lucena, L. Bergmann & P. Azevedo. MCN 2632*, 33 (2 c&s), 19.4–37.7 mm SL, Santana do Livramento , rio Ibirapuitã Chico , 24 Jul 1975, M. E. F. Beurmann, M. I. Vieira & P. C. Braun. MCN 19545*, 2, 35.2–42.5 mm SL, Santana do Livramento , rio Ibirapuitã at Passo do Cerrito , “Área de Proteção Ambiental Ibirapuitã” Conservation Unit , 30º37’37”S 55º40’57”W, 30 Aug 2012, C. L. Castilho, M. A. Azevedo & V. A. Bertaco. UFRGS 17386 , 3 , 26.7–35.8 mm SL, Santana do Livramento , rio Ibirapuitã at Passo do Cerrito , “Área de Proteção Ambiental Ibirapuitã” Conservation Unit, 30º37’37”S 55º40’57”W, 30 Aug 2012, C. L. Castilho, M. A. Azevedo & V. A. Bertaco. UFRGS 27402 *, 1, 39.4 mm SL, Santana do Livramento , arroio Passo das Pedras, “Área de Proteção Ambiental Ibirapuitã” Convervation Unit, 30º32’38”S 55º25’58”W, 29 Aug 2012, C. L. Castilho, M. A. Azevedo & V. A. Bertaco .

Diagnosis. Scleronema ibirapuita is distinguished from all congeners with the exception of S. teiniagua by the absence of the pores s1, s2, s3, and s6 of the supraorbital line of the laterosensory system (vs. presence of, at least, the pore s6). Scleronema ibirapuita differs from S. teiniagua by having the pore i10 of the infraorbital line of the laterosensory system (vs. pore i10 absent) and nine pterygiophores in the dorsal fin (vs. eight).

Description. Based on specimens ranging from 19.4 to 42.5 mm SL; 3 c&s (one dissected). Morphometric data for 18 type specimens in Tab. 4.

External morphology. Greatest height and width of body in half-length of trunk or in dorsal-fin origin. Body elongate, trunk roughly cylindrical gradually compressed towards to caudal fin. Dorsal and ventral profiles of trunk straight to slightly convex. Dorsal and ventral profiles of caudal peduncle straight. Dorsal margin of caudal peduncle with thin membrane, resembling adipose fin. 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 briefly surpassing posterior margin of eye. Maxillary barbel long; emerging from edge of upper lip and extending up to posterior margin of interopercle or briefly surpassing. Basal portion of maxillary barbel wide with thin skin fold 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 lips 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, 6(n = 1), 6/7(n = 3), or 7(n = 39; 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 not visible. Pelvic fin with distal margin convex when expanded, 4/5(n = 2) or 5(n = 41; including holotype) rays; first one always unbranched. Pelvic-fin origin located at half-length of SL 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, 8(n = 2), 9(n = 39; including holotype), or 10(n = 2) rays; first two or three rays unbranched. Dorsal fin with 2(n = 2) procurrent rays. Dorsal-fin origin located at vertical through half-length of pelvic fin. Anal fin with distal margin slightly convex when expanded, 6(n = 43; including holotype) rays; usually first two rays unbranched. Anal fin with 2(n = 2) procurrent rays. Anal-fin origin located at vertical through last third to posterior edge of dorsal-fin base. Caudal fin with distal margin straight and corners slightly rounded, 11(n = 2) or 12(n = 41; 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. Procurrent rays of dorsal, anal and caudal fins rarely visible. Caudal fin with 12(n = 1) or 13(n = 1) procurrent rays dorsally and 9(n = 1) or 10(n = 1) procurrent rays ventrally.

Osteology. Premaxilla with 26–28(n = 1) teeth arranged in three rows. Dentary with 30–32(n = 1) teeth. Opercle with 12–13(n = 2) odontodes and interopercle with 16–18(n = 2) odontodes. Hyoid arch with 6(n = 2) branchiostegal rays. Free vertebrae 33(n = 1) or 35(n = 2); abdominal vertebrae 3(n = 1). Ribs 12(n = 3). First complete haemal arch in 4 th (n = 1) free vertebra, first haemal spine in 12 th (n = 1) free vertebra. Dorsal fin with 9(n = 3) pterygiophores; first one inserted anteriorly to neural spine of 14 th (n = 2) or 15 th (n = 1) vertebra. Anal fin with 6(n = 3) pterygiophores; first one inserted anteriorly to haemal spine of 18 th (n = 1) or 20 th (n = 2) vertebra.

Laterosensory system. Data for 43 specimens summarized in Tab. 3. Canals of laterosensory system with simple (non-dendritic) tubes and external pores. Supraorbital line with nasal canal invariably absent and frontal canal usually absent ( Fig. 5B ) (one of 43 specimens with pore s6). Infraorbital line with antorbital segment invariably absent and sphenotic canal with pores i10 and i11. Posterior segment of frontal, sphenotic and otic canals fused to each other. Otic, posotic and scapular canals present with preoperculo-mandibular and pterotic branches short usually with one pore associated each (po1 and po2, respectively). Trunk canal short with two pores.

Coloration in alcohol. Lateral surface of body with midlateral line of 5–8 round brown blotches larger than opercle over light yellow background ( Fig. 8 ); blotches of some individuals becoming fade or absent towards caudal peduncle. Dorsal surface of body with 5–6 rectangular brown blotches extending ventrally to laterodorsal surface of body. Ventral surface of body light yellow with few brown blotches in caudal peduncle. Dorsal surface of head almost entirely black. Laterodorsal surface of head with numerous brown round blotches over light yellow background. Anterior portion of opercle black. 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 and anal fins with rays faintly brown and distal margins hyaline. Pelvic fin hyaline. Dorsal and caudal fins with vertical light brown stripe basally, rays faintly brown, and distal margins hyaline ( Fig. 8 ).

Geographical distribution. Scleronema ibirapuita occurs in the rio Ibirapuitã basin, a tributary to the left bank of rio Ibicuí ( Brazil), and in the río Arapey ( Uruguay; see remarks); lower rio Uruguay basin ( Fig. 4 ).

Ecological notes. Scleronema ibirapuita inhabits rivers and streams with sand- or gravel-bottoms. The species has not been collected with congeners. The stomach of one specimen had immature aquatic insects and unidentified plant remains.

Etymology. The species epithet “ ibirapuita ” is given in reference to the Conservation Unit “Área de Proteção Ambiental Ibirapuitã”, where the new species can be found and that includes its type locality. A noun in apposition.

Conservation status. Scleronema ibirapuita has an Extent of Occurrence (EOO) of less than 5,000 km 2, but no specific threats were detected to the species. In addition, S. ibirapuita is widespread in streams and rivers draining a Federal Conservation Unit (Área de Proteção Ambiental Ibirapuitã). Thus, the species can be classified as Least Concern (LC) according to IUCN criteria (IUCN, 2019).

Remarks. Scleronema ibirapuita has only one record for the río Arapey basin collected in 1972, Uruguay (ZVC-P 5123; five specimens). Although these specimens have the diagnostic pattern of the laterosensory system for the species, they are listed herein as non-type specimens.

Additional material examined. ZVC-P 5123 , 5 , 26.1–32.2 mm SL, Uruguay, Salto ,

río Arapey Grande near Termas, lower río Uruguay.

Figures

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 8 | Scleronema ibirapuita, new species, holotype (MCN 19470; 39.5 mm SL), Brazil, Rio Grande do Sul, Santana do Livramento, “Área de Proteção Ambiental (APA) Ibirapuitã”, rio Ibirapuitã Chico, rio Ibicuí drainage, lower rio Uruguay.