Trichomycterus melanopygius, REIS ET AL., 2020

Reis, Vinícius & Pinna, Mário De, 2023, Diversity and systematics of Trichomycterus Valenciennes 1832 (Siluriformes: Trichomycteridae) in the Rio Doce Basin: iterating DNA, phylogeny and classical taxonomy, Zoological Journal of the Linnean Society 197, pp. 344-441 : 412-416

TRICHOMYCTERUS MELANOPYGIUS REIS ET AL., 2020

( FIG. 31)

Trichomycterus melanopygius Reis, dos Santos, Britto, Volpi & de Pinna, 2020: 4 , figs 1–3 [type locality: Brazil, state of Minas Gerais, Rio Doce Municipality , Rio Doce Basin, Córrego dos Borges , stream flowing into left bank of Risoleta Neves Reservoir, (20°12’21.63”S 42°52’56.24”W)]; col. V.J.C. Reis, M.C.C. de Pinna, G.F. de Pinna & G. Ballen, 24 June 2018.

Diagnosis: The combination of the following traits distinguishes T. melanopygius from its congeners: (1) the combination of invariably uniform body coloration with a horizontal dark stripe in the middle of caudal fin; (2) pectoral-fin rays I + 7 (vs. I + 5, I + 6 or I + 8); (3) post-Weberian vertebrae 38–40 (vs. fewer). Among congeners in south-eastern South America, character 1 distinguishes T. melanopygius from all species except young stages of T. immaculatus ; character 2 distinguishes it from all species in the T. brasiliensis and T. reinhardti species complex ( Barbosa & Costa, 2010; Costa, 2021; Costa & Katz, 2021), plus T. trefauti (with I + 6 or fewer) and from T. astromycterus , T. caipora , T. giganteus , T. immaculatus , T. lauryi , T. nigricans and T. tantalus (with I + 8 or more); character 3 distinguishes T. melanopygius from all congeners except for T. candidus , T. claudiae , T. gasparinii and T. novalimensis . Among congeners in the Rio Doce Basin , T. melanopygius is most similar to T. immaculatus . In addition to characters above, T. melanopygius can be further distinguished from T. immaculatus by a number of anatomical features: (1) hyomandibula narrow, with a deep concavity at middle of its dorsal margin (vs. hyomandibula wide, with a small and attenuated dorsal concavity; Reis et al., 2020: fig. 4); (2) opercular patch of odontodes small, its height 10.3–14.3% HL (vs. 14.9–20%); (3) differently shaped urohyal, with a slender head and wide wings (vs. a wide head and slender wings) ( Reis et al., 2020: figs 5–6); (4) uncinate process of second epibranchial long and undivided (vs. short and forked; Reis et al., 2020: fig. 7); and (5) third pharyngobranchial thin (vs. thick; Reis et al., 2020: fig. 7). In addition to morphological distinctions, the barcoding distance between T. melanopygius and T. immaculatus is 3.8% ( Table 2).

Description: Morphometric data for specimens examined is presented in Table 13. Body long and almost straight, trunk roughly round in cross-section near head, then slightly deeper than broad and gently compressed to caudal peduncle, tapering to caudal fin. Dorsal profile of body gently convex to dorsal-fin origin, then straight or slightly concave along caudal peduncle to caudal-fin origin. Ventral profile convex from gular region to vent, due partly to abdominal distension, then straight or slightly concave along anal-fin origin to caudal-fin base. Caudal peduncle as deep as body at beginning of anal-fin base.

Head approximately 1/4 of SL, pentagonal, longer than wide and depressed. Mouth subterminal. Upper jaw slightly longer than lower. Upper lip wider than lower lip and laterally continuous with base of maxillary barbel. Lower lip small, approximately 2/3 width of upper one, partly divided into right and left portions by with median concavity. Lower lip with uniform covering of tiny villi, resulting in velvet-like surface and not clustered into large papillae. Region between upper and lower lips with slender fleshy lobe.

Dentary and premaxillary teeth similar to each other in shape. Dentary teeth conical, 43–57 arranged in four irregular rows, first row with 10–13 teeth, extending from base to slightly above the coronoid process, with size of individual teeth increasing markedly towards symphysis and from posterior to anterior rows. Total area of premaxillary teeth slightly smaller than that of dentary, with 45–60 teeth arranged irregularly in four rows, first row with approximately 12–13 teeth, over entire ventral surface of premaxilla. Premaxillary teeth conical.

Eye medium-sized, protruding, positioned dorsally on head, without free orbital rim and covered with transparent skin. Eye located on anterior half of HL, closer to lateral border of head than to the midline in dorsal view. Anterior naris surrounded by tube of integument directed anterolaterally, continuous posterolaterally with nasal barbel. Posterior naris closer to anterior naris than to eyes, surrounded by tube of integument incomplete posteriorly. Maxillary barbel narrowing markedly towards fine tip, reaching from lateroposterior side of interopercle until base of pectoral fin. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching from anterolateral to the middle of interopercle. Nasal barbel originating on posterolateral region of anterior naris, reaching from posterior border of eyes to anterior portion of opercle. Interopercular patch of odontodes large, oval in shape and with well-developed odontodes, prominent in ventral aspect of head. Interopercular patch of odontodes extending from vertical through ventroposterior border of eye to ventroanterior to opercle patch of odontodes. Interopercular odontodes arranged in two or three irregular series, with those on mesial series much longer than those on lateral one; odontodes gradually larger posteriorly in both series, with those posteriorly on mesial row largest. Interopercular odontodes 39–51. Opercular patch of odontodes on dorsolateral surface of posterior part of head, positioned anterodorsally to pectoral-fin base, roundish in shape and larger than eye in dorsal aspect of head. Opercular odontodes 18–23, sunk in individual slits of integument, progressively larger posteriorly, all with fine tips, with largest ones curved distally and claw-like. Entire patch surrounded by fleshy fold rim of integument.

Pectoral fin with its base immediately posterior and ventral to opercular patch of odontodes. Pectoral-fin rays I + 7 or rarely I + 8. First pectoral-fin ray (unbranched) longer, prolonged as filament beyond fin margin. Other rays progressively less longer, their tips following continuous line along fin margin. Pelvic fin with convex distal margin, its origin slightly posterior to middle of SL and anterior to vertical through dorsal-fin origin, covering anal and urogenital openings in adults. Base of pelvic fins positioned close to each other. Pelvic-fin rays I + 4, first ray unbranched. Anterior process of basipterygium short and thin. Dorsal fin long, its distal profile sinusoidal. Dorsal-fin origin closer to base of caudal fin than to tip of snout. Dorsal-fin rays iii + II + 7 (6) or iii + II + 6 (1), three unsegmented and unbranched rudimentary rays, two segmented and unbranched procurrent rays and six or seven branched and segmented rays. Anal fin slightly smaller than dorsal fin, its distal margin gently convex. Anal-fin origin posterior to vertical through end of dorsal-fin base. Anal-fin rays ii + II + 5 (2) or iii + II + 5 (5), two unsegmented and unbranched rudimentary rays, two segmented and unbranched procurrent rays and five branched and segmented rays. Caudal fin round to subtruncate, with 6 + 7 principal rays.Adipose fin absent or modified into low integumentary fold extending between end of dorsal fin and caudal-fin origin. Post-Weberian vertebrae 38 (5), 39 (2) or 40 (1). First dorsal-fin pterygiophore immediately anterior to neural spine of 18 th (1), 19 th (3) or 20 th (1) vertebra, first anal-fin pterygiophore immediately anterior to haemal spine of 22 th (7) or 23 rd (2) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally. Procurrent caudal-fin rays 17–22 (9) dorsally and 14–16 (9) ventrally, beginning anteriorly at 34 th (1) or 35 th (1) vertebrae. Ribs 12 (1), 13 (5) or 14 (2). Branchiostegal rays 7 (5) or 8 (2). Dorsal-fin pterygiophores 8. Anal-fin pterygiophores 6.

Cephalic lateral line canals with simple, non-dendritic tubes ending in single pores. Supraorbital canal mostly in frontal bone. Supraorbital pores invariably present: s1 mesial to nasal-barbel base and autopalatine, s3 mesial to posterior nostril and anterior to frontal and paired s6 posteromedial to eye and at midlength of frontal. Infraorbital laterosensory canal incomplete with four pores, i1 and i3 anteriorly and i10 and i11 posteriorly. Canal extending from sphenotic posteriorly to terminal pore located ventroposteriorly to eye. Infraorbital pore i1 located ventrolateral to nasal-barbel base and autopalatine, i3 ventro-lateral to posterior nostril and anterior to frontal, i10 and i11 posterior to eye. Otic canal without pores. Postotic pores po1, anteromedial to opercular patch of odontodes, and po2, mesial to opercular patch of odontodes. Lateral line of trunk anteriorly continuous with postotic canal and reduced to short tube. Lateral line pores ll1 and ll2 dorsomedial to pectoral-fin base.

Coloration in ethanol: Dorsal and lateral parts of body covered with uniform scattering of dark chromatophores on inner and outer layers of skin, not forming maculae or spots. Ventral part of body, from lower lip to anal-fin base, without pigment. Dorsal and anal fins darkly pigmented, but each with conspicuous unpigmented band longitudinally along their middle portion. Caudal fin with broad longitudinal dark stripe from base of middle caudal-fin rays nearly to margin of fin. Caudal stripe more evident in young specimens (a pattern similar to that in T. ipatinga and T. tantalus ). Integument surrounding opercular odontodes darkly pigmented. Interopercular patch of odontodes without dark pigment. In life, T. melanopygius has the same basic coloration pattern, but with more vivid colours and less opaque integument and fins ( Reis et al., 2020: fig. 3). The body is a uniform brown colour, slightly darker on head. Pectoral-, dorsal- and caudal-fin rays are finely outlined in dark and the longitudinal caudal-fin stripe is conspicuously visible.

Remarks: Trichomycterus melanopygius is easily mistaken for T. immaculatus , due to some similarities such as the uniformly dark colour pattern (similar to the most common colour morph of the latter species) and the first pectoral-fin ray prolongued as a long filament. However, T. melanopygius is distinguished from T. immaculatus by several additional morphological and molecular features, such as I + 7 pectoral-fin rays, rarely I + 8 (vs. invariably I + 8 for T. immaculatus ), 38–40 post-Weberian vertebrae (vs. 34 to 37 in T. immaculatus ), by the more posteriorly positioned first dorsal-fin pterygiophore (anterior to neural spine 18–20 vs. 16 or 17 in T. immaculatus ) and by the different shape of some bones, as presented in the original description ( Reis et al., 2020). Additionally, T. melanopygius is well-differentiated by DNA barcoding, with 3.8% divergence from T. immaculatus (against 0.3% intraspecific divergence). Phylogenetically, the species is not closely related to T. immaculatus , instead forming a clade with T. aff. caipora , T. ipatinga and T. tantalus . Despite clear-cut morphological distinctiveness of the species, samples of T. melanopygius do not form a monophyletic group on the basis of COI data.

Geographical distribution: Trichomycterus melanopygius is distributed in tributaries throughout the Rio Doce Basin. It has so far not been recorded from the main channel ( Fig. 32). This distribution pattern is similar to that of T. ipatinga (see later species for additional information).

Type material examined: all from Brazil, state of Minas Gerais, Rio Doce Basin. Holotype: MZUSP 123762, 64.0 mm SL, Córrego dos Borges, stream flowing into left bank of Risoleta Neves Reservoir. Paratypes: MNRJ 38472, 2, 34.2–38.7 mm SL; Catas Altas, Rio Conceição , tributary to Rio Piracicaba (20°0’20”S 43°30’28”W); col. M.R. Britto & J. Gomes, 28 November 2010; MNRJ 46933, 2, 51.9 (c&s), 59.1 mm SL; Conceição do Mato Dentro, Córrego Pica-Pau, tributary to Ribeirão Santo Antônio (also called Cruzeiro) (18°46’58”S 43°33’11”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 5 March 2016. MNRJ 46926, 5, 29.6–65.1 mm SL; Conceição do Mato Dentro, Ribeirão Santo Antônio (also called Cruzeiro), near confluence with Pica-Pau Creek (18°47’0”S 43°33’37”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 5 March 2016; MNRJ 48462, 5, 37.9–97.2 mm SL; Conceição do Mato Dentro, Santo Antônio Stream (also called Cruzeiro), near confluence with Pica-Pau Creek (18°47’0”S 43°33’37”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 30 July 2016; MNRJ 48469, 1, 95.0 mm SL; Conceição do Mato Dentro, Pica-Pau Creek, tributary of Santo Antônio Stream (also called Cruzeiro) (18°47’1”S 43°33’23”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 30 July 2016. MZUSP 94508, 1, 34.7 mm SL; Desterro de Melo, Ribeirão Xopotó, at bridge in town of Desterro de Melo (21°8’53”S 43°30’46”W); col. O.T. Oyakawa, E. Baena & M. Loeb, 10 July 2007; MZUSP 94537, 1, 41.1 mm SL; Desterro de Melo, Ribeirão Xopotó at entrance of town of Desterro de Melo (21°9’10.00”S 43°31’28.00”W); col. O.T. Oyakawa, E. Baena & M. Loeb, 10 July 2007; MZUSP 110714, 1, 69.1 mm SL; Itambé do Mato Dentro, Tanque River (19°25’28.00”S 43°12’1.00”W); col. A. de Castro & R. Pádua, 5 August 2010; MZUSP 110932, 2, 28.3– 100.7 mm SL; Mariana, Rio Gualaxo do Sul (20°30’16.97”S 43°24’39.28”W); col. L.F. Salvador Jr. & L.A.C. Missiaggia, 5 July 2012. MZUSP 110936, 97.7 mm SL; Mariana, Gualaxo do Sul River (20°25’59.995”S 43°23’46.756”W); col. L.F. Salvador Jr. & L.A.C. Missiaggia, 5 June 2012. MZUSP 112748, 4, 37.2–49.2 mm SL, 2 c&s (42.8–49 mm SL); Ferros, Santo Antônio River, at bridge in downtown Ferros (19°13’34.5”S 43°1’9.5”W); col. O.T. Oyakawa & T.F. Teixeira, 16 August 2012.

Additional material studied: All from Brazil, Rio Doce Basin. MZUSP 121713, 6, 16.7–22.4 mm SL, 2 c&s, 17.5– 17.8 mm SL; Coronel Fabriciano, cachoeira da Limeira, Rio Piracicaba , state of Minas Gerais (19°23’42.63”S 42°42’51.30”W); col. V.J.C. Reis, 22 March 2017. MBML 54, 2, 44.8–46.0 mm SL; Colatina, Santa Maria do Rio Doce River , state of Espírito Santo (19°36’14.00”S 40°37’13.00”W); col. R.L. Teixeira & J.A.P. Scheneider, 29 August 1996. MBML 701, 3, 36.5–71.9 mm SL; Itarana, Rio Santa Joana, state of Espírito Santo (19°52’26.00”S 40°52’31.00”W); col. R.L. Teixeira & P.S. Miller, 19 August 2000. MBML 1049, 1, 107.0 mm SL; Santa Teresa, Córrego Vinte e Cinco de Julho, Santa Maria do Rio Doce River , state of Espírito Santo (19°56’8.00”S 40°36’1.00”W); col. R.L. Teixeira, 19 March 2005. MBML 6151, 1, 65.3 mm SL; Santa Teresa, Cinco de Novembro Tiver (tributary to Santa Maria do Rio Doce River ), next to road ES-080 to Santo Antônio do Canaã, state of Espírito Santo (19°50’26.00”S 40°37’47.30”W); col. C.J. Cunha, J.P. Silva & R.B. Soares, 20 August 2012. MNRJ 38505, 1, 42.4 mm SL; Catas Altas, Córrego do Frade (tributary of Ribeirão Caraça), state of Minas Gerais (20°7’53”S 43°34’21”W); col. M.R. Britto & J. Gomes, 12 January 2010. MNRJ 42073, 2, 28.5–39.0 mm SL; Catas Altas, Córrego do Engenho (tributary of Ribeirão Caraça), state of Minas Gerais (20°2’9”S 43°29’28”W); col. M.R. Britto, D.F. Moraes Jr. & D. Almeida, 6 October 2013. MNRJ 45816, 1, 25.6 mm SL; Conceição do Mato Dentro, Rio Parauninha (tributary of Santo Antônio River), at Baú Village, state of Minas Gerais (18°56’16”S 43°38’30”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 2 March 2016. MNRJ 46854, 1, 24 mm SL; Congonhas do Norte, Rio Lambari (also called Cachoeira do Jacu) (left-hand tributary to Rio Parauninha ), at Coqueiros Village, state of Minas Gerais (18°52’43”S 43°37’23”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 2 March 2016. MNRJ 46865, 1, 88.8 mm SL; Congonhas do Norte, Rio Lambari (also called Cachoeira do Jacu) (left-hand tributary to Rio Parauninha ), at bridge at road Conceição do Mato Dentro-Congonhas do Norte, state of Minas Gerais (18°53’43”S 43°36’34”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 2 March 2016. MNRJ 47902, 1, 85.4 mm SL; Alvorada de Minas, Ribeirão das Pedras (right-hand tributary to Rio do Peixe), state of Minas Gerais (18°45’43”S 43°25’45”W); col. R.F. Miranda, A. Correia & M. Castro, 22 December 2015. MNRJ 48404, 1, 32 mm SL; Conceição do Mato Dentro, Rio Parauninha (right-hand tributay to Santo Antônio River), upstream of Candeias Village, state of Minas Gerais (18°56’16”S 43°38’29”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 2 August 2016. MNRJ 48477, 1, 31.8 mm SL; Conceição do Mato Dentro, Ribeirão Santo Antônio do Norte (tributay to Santo Antônio River), upstream of Santo Antônio do Norte Village, state of Minas Gerais (18°47’54”S 43°31’0”W); col. S.A. dos Santos, D.F. Moraes Jr. & M.R. Britto, 30 July 2016.