Trichomycterus santaeritae ( Eigenmann, 1918 )

Costa, Wilson J. E. M., Katz, Axel M., Mattos, José Leonardo O., Amorim, Pedro F., Mesquita, Beatrizz O., Vilardo, Paulo J. & Barbosa, Maria Anais, 2020, Historical review and redescription of three poorly known species of the catfish genus Trichomycterus from south-eastern Brazil (Siluriformes: Trichomycteridae), Journal of Natural History 53 (47 - 48), pp. 2905-2928 : 2919-2922

Trichomycterus santaeritae ( Eigenmann, 1918)

( Figure 1c , 2g –i )

Pygidium santaeritae Eigenmann, 1918: 341 (holotype: FMNH 58577 , 18 mm SL (photographs and radiographs available at https://collections-zoology.fieldmuseum.org/catalo gue/637070; type locality: Santa Rita [presently Santa Rita do Jacutinga , Minas Gerais, south-eastern Brazil], Rio Preto [tributary of the Rio Paraibuna , Rio Paraíba do Sul basin]).

Pygidium florense P. Miranda Ribeiro, 1943: 1–2 (holotype: MNRJ 3751 , 44 mm in total length; type locality: Rio das Flores [a tributary of the Rio Preto , Rio Paraibuna drainage, Rio Paraíba do Sul basin], near Ipiabas , at Estação Pandiá Calógeras [Município de Barra do Piraí, Estado do Rio de Janeiro).

Material examined

All material from the Rio Preto drainage, tributary of the Rio Paraibuna , Rio Paraíba do Sul basin, south-eastern Brazil . Estado de Minas Gerais: Município de Santa Rita do Jacutinga: – FMNH 58577 , holotype, 18 mm SL; Santa Rita ( Santa Rita do Jacutinga ), about - 22.14166S, - 44.09166W, about 560 m asl; J . Haseman, 10 July 1908. – UFRJ 5436 , 1 ; village of Santa Rita do Jacutinga , - 22.14166S, - 44.09166W, about 560 m asl; W .J.E.M. Costa et al., 29 March 2002. – UFRJ 12592 , 3 ; UFRJ 12408, 2 (DNA); Ribeirão Santana, tributary of Rio Preto , - 22.04861S, - 44.83333W, about 625 m asl; B . Mesquita et al., 1 September 2019. – UFRJ 12589 , 3 (C&S); UFRJ 12409, 3 (DNA); Ribeirão Santana, tributary of Rio Preto, near Cachoeira do São Jorge ; B . Mesquita et al., 1 September 2019. Estado do Rio de Janeiro: – MNRJ 3751 , holotype of Pygidium florense ; Município de Barra do Piraí: Rio das Flores, near Ipiabas, at Estação Pandiá Calógeras , about - 22.39027S, - 43.86944W about 685 m asl; A .L. Gomes. – UFRJ 595 , 8 ex .; UFRJ 646, 1 (C&S); Município de Valença: Rio Bonito , tributary of Rio das Flores, Conservatória, - 22.28972S, - 43.914167W, about 529 m asl; W .J.E.M. Costa and C.P. Bove, 7 September 1991.

Diagnosis

Trichomycterus santaeritae differs from all other congeners, except T. caipora , T. giganteus , T. immaculatus , T. nigricans and T. pradensis , by having 9 pectoral-fin rays (vs 6–8). Trichomycterus santaeritae is distinguished from all other species here osteologically examined, except T. caipora , T. immaculatus , T. nigricans and T. pradensis , by the presence of a pronounced posterior process on the maxilla ( Figure 2g ) (vs rudimentary process). Also distinguished from all congeners, except T. caipora , T. immaculatus and T. nigricans , by having the caudal fin emarginate at least in larger specimens (vs truncate or subtruncate, rarely bilobed). Trichomycterus santaeritae is distinguished from T. caipora , T. immaculatus and T. nigrican s by having a more anteriorly positioned dorsal fin, its origin in a vertical through the centrum of the 15th or 16th vertebra (vs between the centrum of the 17th or 19th vertebrae), fewer ribs (9–10 vs 11–13), a large eye (eye diameter 14.7– 21.3% of the head length, vs 9.2–13.1%) and a distinct colour pattern consisting of trunk pale yellow with dark brown transverse bars and spots (vs never a similar colour pattern).

Description

Morphometric data are given in Table 1. Largest specimen examined 74.2 mm SL. Body moderately slender, subcylindrical and slightly depressed anteriorly, compressed posteriorly. Greatest body depth at vertical just anterior to pelvic fin base. Dorsal profile of head and trunk slightly convex, approximately straight on caudal peduncle; ventral profile straight to slightly convex between lower jaw and end of anal-fin base, straight on caudal peduncle. Skin papillae minute. Anus and urogenital papilla in vertical through posterior half of dorsal-fin base. Head trapezoidal in dorsal view. Anterior profile of snout slightly convex in dorsal view. Eye relatively large, dorsally positioned in head. Posterior nostril located nearer anterior nostril than orbital rim. Tip of maxillary barbel reaching between middle and posterior portion of opercular patch of odontodes; tip of rictal barbel reaching posterior third of interopercular patch of odontodes; tip of nasal barbel reaching point just anterior to opercular patch of odontodes. Mouth subterminal. Jaw teeth arranged in 3 or 4 irregular rows, sharply pointed in internal rows, gradually becoming incisiform on outermost rows; premaxillary teeth nearly straight, dentary teeth slightly curved inside mouth. Branchial membrane attached to isthmus only at its anterior point. Branchiostegal rays 7 or 8.

Dorsal and anal fins subtriangular; total dorsal-fin rays 12–14 (iii + II + 7–9), total anal-fin rays 10 (iii + II + 5); anal-fin origin posterior to dorsal-fin base. Dorsal-fin origin in vertical through centrum of 15th or 16th vertebra; anal-fin origin in vertical between centrum of 22nd or 23rd vertebra. Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in long filament reaching about 40–50% of pectoral-fin length without filament; total pectoral-fin rays 9 (I + 8). Pelvic fin truncate, its posterior extremity reaching urogenital papilla; pelvic-fin bases medially separated by broad interspace, its length about equal to pelvic-fin base length; total pelvic-fin rays 5 (I + 4). Caudal fin emarginated, upper and lower corners rounded to slightly pointed in larger specimens; total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 14–16 (xiii–xv + I), total ventral procurrent rays 10–14 (ix–xiii + I). Vertebrae 35–36. Ribs 9 or 10. Two dorsal hypural plates, corresponding to hypurals 4 + 5 and 3, respectively; single ventral hypural plate corresponding to hypurals 1 and 2 and parhypural.

Laterosensory system. Supraorbital sensory canal continuous, connected to posterior section of infraorbital canal posteriorly. Supraorbital sensory canal with 3 pores: s1, adjacent to medial margin of anterior nostril; s3, adjacent and just posterior to medial margin of posterior nostril; and s6, in transverse line through posterior half of orbit; single s6 on top of head. Infraorbital sensory canal arranged in 2 segments, each with 2 pores; anterior segment with pore i1, in transverse line through anterior nostril, and pore i3, in transverse line just anterior to posterior nostril; posterior segment with pore i10, adjacent to ventral margin of orbit, and pore i11, posterior to orbit. Postorbital canal with 2 pores: po1, in vertical line above posterior portion of interopercular patch of odontodes, and po2, in vertical line above posterior portion of opercular patch of odontodes. Lateral line of body short, with 2 pores, posterior-most pore in vertical just posterior to pectoral-fin base.

Mesethmoidal region and adjacent structures ( Figure 2g ). Anterior margin of mesethmoid gently concave, mesethmoid cornu robust, subcylindrical, tip rounded. Antorbital and sesamoid supraorbital narrow, rod-like, sesamoid supraorbital long, its length about 2.5 times antorbital length. Premaxilla sub-rectangular in dorsal view, with minute lateral process. Maxilla boomerang-shaped, slender, longer than premaxilla, slightly curved, with prominent posterior process. Autopalatine sub-rectangular in dorsal view when excluding posterolateral process, narrow, its shortest width about one-third autopalatine length, lateral and medial margins slightly concave; latero-posterior process of autopalatine triangular, long, its length about two-thirds autopalatine length. Posterior articulatory process well developed, shell-shaped.

Suspensorium and opercular apparatus ( Figure 2h ). Metapterygoid subtriangular, longer than deep, anterior face curved, posterior and ventral face nearly straight, posterior margin separated by anterior hyomandibula flap by small interspace. Quadrate robust, dorsoposterior flap continuous to hyomandibula flap. Hyomandibula broad, with well-developed flap; middle portion of dorsal margin of hyomandibula flap with shallow concavity; posterodorsal process of hyomandibula moderate, pointed. Opercle robust, its smallest depth about half opercle length; dorsal process of opercle short and blunt, about one-third opercle length; ventral process of opercle moderate, about equal to opercle length; odontode patch relatively deep, its depth about three-quarters opercle length, with about 25–30 odontodes; odontodes pointed, arranged in irregular transverse rows. Interopercle long, about twothirds hyomandibula length; dorsal interopercular process with deep anterior concavity; interopercular odontode patch relatively long, its length about 2.5 times depth of opercular odontodes patch, with about 65–70 odontodes; odontodes pointed, arranged in irregular longitudinal rows. Preopercle compact, with pronounced ventral flap.

Branchial arches ( Figure 2i ). Basibranchial 2 and 3 subcylindrical, basibranchial 2 slightly longer and distinctively wider, basibranchial 3 slightly constricted in its medial portion; basibranchial 4 cartilage pentagonal, longer than wide. Hypobranchial 1 subcylindrical; hypobranchial 2 and 3 subtriangular, anterior extremity of hypobranchial 3 branched. Ceratobranchial 1 moderately broad in its proximal tip, narrowing to its distal tip; ceratobranchials 2 and 3 widened in their middle portion, with shallow concavity on posterior margin of basal portion; ceratobranchial 4 sub-rectangular; ceratobranchial 5 sub-rectangular, postero-proximal portion bearing patch of small, slightly curved, conical teeth. Epibranchial 1 slender, with well-developed anterior uncinate process; epibranchial 2 slender, with rudimentary anterior uncinate process; epibranchial 3 slender, with well-developed, curved posterior uncinate process; epibranchial 4 broad, subretangular, proximal portion broader than distal portion; epibranchial 5 cartilage (= accessory element of ceratobranchial 4) minute. Pharyngobranchial 3 short, subcylindrical; pharyngobranchial 4 long, bearing broad dentigerous tooth-plate with curved conical teeth.

Colouration in life ( Figure 1c ). Colour ground on trunk pale yellow, becoming clearer ventrally; 6 or 7 transverse dark brown bars on dorsum and dorsal portion of flank; horizontal row of dark brown spots along midline of flank, united with dorsal transverse bars in smaller specimens, separated in specimens above 50 mm SL; similar horizontal row of smaller spots on ventral part of flank, between vertical just posterior to pelvic-fin base and caudal-fin base; minute patches of dark chromatophores irregularly arranged on antero-ventral part of flank. Venter yellowish white. Head pale orange to yellowish white ventrally, with small brown spot just anterior to opercular patch of odontodes; opercular and interopercular patch of odontodes white, posterior opercular membrane black; nasal barbel dark grey on its proximal portion, white on distal portion, maxillary and rictal barbels white; area between and around nostrils dark brown; iris pale orangish yellow. Fins yellowish hyaline, sometimes dark chromatophores scattered on caudal-fin base. No colouration polymorphism recorded.

Colouration in alcohol. Similar to colouration in life, but with paler colours.

Distribution and habitat

Trichomycterus santaeritae occurs in a vast area of the lower section of the Rio Preto drainage ( Figure 3 ). It has been found in clearwater rivers and streams, always associated with sandy stretches on the river bottom, in places with high water flow, actively swimming at daylight.

Figures

Figure 1. Live specimens, left lateral view, of: a, Trichomycterus nigricans, UFRJ 10,996, 69.7 mm SL; b, Trichomycterus immaculatus, UFRJ 12,050, 62.9 mm SL; c, Trichomycterus santaeritae, UFRJ 12,592, 56.8 mm SL. All were photographed a few hours after collection.

Figure 2. Osteological features of Trichomycterus nigricans (a–c), T. immaculatus (d–f), and T. santaeritae (g–i): A, D, G, mesethmoidal region and adjacent structures, middle and left portion, dorsal view; B, E, H, left suspensorium and opercular apparatus, lateral view; C, F, I, middle and left portion of brachial arches, ventral view of dorsal elements on left, dorsal view of ventral elements on right. Larger stippling represents cartilage. Abbreviations: aip, anterior interopercular projection; b2–3, basibranchials 2–3; bc4, cartilaginous basibranchial 4; c1–5, ceratobranchials 1–5; e1–4, epibranchials 1–4; ec5, epibranchial 5 cartilage (= accessory element of ceratobranchial 4); h1–3, hypobranchials 1– 3; hdb, hypobranchial anterior branching; pmp, posterior maxillary process; p3, pharyngobranchial 3; pt4, pharyngobranchial 4 tooth-plate.

Figure 3. Geographical distribution of the Trichomycterus nigricans species group: diamonds, T. santaeritae; square, T. caipora; stars, T. immaculatus; triangles, T. nigricans.