Trichomycterus reinhardti, (EIGENMANN, 1917)

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 : 417-424

TRICHOMYCTERUS REINHARDTI (EIGENMANN, 1917)

( FIG. 33)

Pygidium reinhardti Eigenmann, 1917: 699 [type locality: Rio Itabira at Burmier (probably Miguel Burnier, a district of the municipality of Ouro Preto), tributary of Rio das Velhas , Brazil; holotype (unique): FMNH 58081, ex CM 7078]; Eigenmann, 1918: 333 (redescription); Henn, 1928: 80 (type catalogue); Ibarra & Stewart, 1987: 73 (type catalogue); Ferraris, 2007: 422 (checklist).

Trichomycterus reinhardti Burgess, 1989: 323 (list); Fernández & Bichuette, 2002: 278 (comparison); de Pinna & Wosiacki in Reis et al., 2003: 283 (checklist); Wosiacki & Garavello, 2004: 3 (list); Bockmann & Sazima, 2004 (colour comparison); Bockmann et al., 2004: 227 (cited); Sato et al., 2004 (cytogenetics);Alencar & Costa, 2006: 48 (diagnosis); Ferraris, 2007: 422 (checklist); Barbosa & Costa, 2010: 121 (comparison); Datovo et al., 2012: 36 (comparative material); Katz et al., 2013 (diagnosis); Donin et al., 2020: 16 (comparison), Ochoa et al., 2017 (relationships); Ochoa et al., 2020 (relationships); Costa & Katz, 2021:18 (phylogeny); Costa, 2021 (taxonomic discussion).

Diagnosis: The combination of the following traits distinguishes T. reinhardti from congeners: 1— broad mid-lateral dark stripe with notched edges extending from posterior margin of opercle to base of caudal fin; 2—reduced opercular armature, with 6–7 odontodes (vs. count more numerous); 3—pectoral-fin rays I + 5, (vs. I + 6, I + 7 or I + 8); 4—horizontal dark stripe along middle caudal-fin rays, more evident in juvenile specimens (vs. stripe absent); 5—pelvic-fin rays I + 4 (vs. I + 3); 6—ribs 14 (vs. 16–19). Among congeners in south-eastern South America, character 1 distinguishes T. reinhardti from all congeners except for Trichomycterus anaisae Costa & Katz, 2021 , Trichomycterus funebris Costa & Katz, 2021 , T. humboldti Costa & Katz, 2021 , Trichomycterus ingaiensis Costa & Katz, 2021 , Trichomycterus luetkeni Costa & Katz, 2021 , T. pauciradiatus Alencar & Costa, 2006 , T. piratymbara Katz et al., 2013 , T. sainthilairei Costa & Katz, 2021 and Trichomycterus septemradiatus Katz et al., 2013 ; character 2 from all congeners; character 3 from all congeners except for T. humboldti , T. sainthilairei , T. pauciradiatus and T. piratymbara ; character 4 from all congeners except for T. immaculatus , T. ipatinga , T. melanopygius , T. reinhardti species complex ( Costa & Katz, 2021) and T. tantalus ; character 5 from T. humboldti and T. pauciradiatus ; character 6 from T. piratymbara , T. funebris , T. ingaiensis and T. sainthilairei .

Description: Morphometrics in Table 14. Body long and almost straight, trunk roughly round in cross-section near head, then slightly deeper than wide and gently compressed towards caudal peduncle, tapering to caudal fin. Dorsal profile of body straight or 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 almost as deep as body at beginning of anal-fin base.

Head approximately 1/5 of SL, roughly pentagonal, slightly longer than wide and depressed. Mouth subterminal. Upper jaw slightly longer than lower one. Upper lip wider than lower lip, 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 median concavity. Lower lip with uniform covering of tiny villi, not clustered into large papillae, resulting in velvet-like surface. Region between upper and lower lips with slender fleshy lobe.

Dentary and premaxillary teeth similar to each other in shape. Dentary teeth conical, 27–30, arranged in three or four irregular rows, first row extending from base to slightly up of coronoid process, with size of individual teeth increasing markedly towards symphysis and from posterior to anterior rows. Premaxillary teeth conical, 26–27, arranged in three or four irregular rows over entire ventral surface of premaxilla. Total area of premaxillary teeth visually slightly smaller than that of dentary.

Eye slightly protruding, positioned dorsolaterally 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, rimmed anteriorly by flap of integument. Maxillary barbel narrowing markedly towards fine tip, reaching pectoral-fin base. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching margin of interopercular patch of odontodes. Nasal barbel originating on posterolateral region of anterior naris, reaching posterior portion of opercular patch of odontodes. Interopercular patch of odontodes medium to large compared to head length, oval in shape and with well-developed odontodes, prominent in ventral aspect of head. Interopercular patch of odontodes extending from vertical through posterior margin of eye to vertical through anterior margin of opercular patch of odontodes. Interopercular odontodes 19 or 20, arranged in three or four irregular series, with those on mesial series longer than those on lateral one; odontodes gradually larger posteriorly in all series, with those posterior on mesial row largest. 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 6–7, 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 rim of integument.

Pectoral fin with its base immediately posterior and ventral to opercular patch of odontodes. Pectoral-fin rays I + 5 (3). First pectoral-fin ray (unbranched) longer, prolonged as filament beyond fin margin, with variable length. Other rays progressively shorter, their tips following continuous line along fin margin. Pelvic fin with convex distal profile, slightly covering anal and urogenital openings in adults, its origin slightly posterior to middle of SL and anterior to vertical through dorsal-fin origin. Bases of pelvic fins separated by one eye diameter. Pelvic-fin rays I + 4. Anterior processes of basipterygium long and thin. Dorsal fin long, its distal margin sinusoidal. Dorsal-fin origin closer to base of caudal-fin than to tip of snout. Dorsal-fin rays ii + II + 7(2). 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). Caudal fin truncated with round edges, with 6 + 7 principal rays. Adipose fin absent or represented by low integument fold extending between end of dorsal fin and caudal-fin origin. Post-Weberian vertebrae, 37(1) and 38 (1). First dorsal-fin pterygiophore immediately anterior to neural spine of 20 th (1), vertebra, first anal-fin pterygiophore immediately anterior to neural spine of 22 nd (1) and 23 rd (1) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally. Procurrent caudal-fin rays, 20 - 21 dorsally and 13 - 15 ventrally, beginning anteriorly at vertebrae 31. Ribs 14 (1), 15 (1). Branchiostegal rays 8. 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 latero-sensory canal incomplete, with four pores, i1 and i3 anteriorly and i10 and i11 posteriorly, extending from sphenotic posteriorly to terminal pore located ventroposteriorly to eye. Infraorbital pore i1 located ventrolateral to nasal-barbel base and autopalatine, i3 ventrolateral 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: Trichomycterus reinhardti has a distinct colour pattern that changes only slightly during development. In adults, basic pigmentation consisting of broad dark mid-lateral stripe, covering nearly 1/3 of body depth in lateral view and extending from posterior border of opercle to base of caudal fin. Stripe with notched edges formed by small dark spots usually overlapping each other. Long area dorsal and ventral to mid-lateral stripe, forming trailing white bands highlighting latter. On dorsum, colour pattern ranging from broad dark mid-dorsal band consisting of tiny dark spots occupying almost entire dorsum to three rows of round small maculae longitudinally arranged along dorsum: mid-dorsal row along entire dorsum from occiput to dorsal edge of caudal peduncle (forming a broad cloudy band in some adults and all young specimens), two rows ventrolaterally on each side of mid-dorsal one, extending from base of head to base of caudal fin. In young specimens, latter row consisting of small dark spots, forming notched edge. Ventral to mid-lateral stripe, row of tiny dark spots, less conspicuous and shorter than dorsal ones, extending along posterior part of abdomen, through midlength of body to base of caudal fin. Ventral side of abdomen lacking dark pigment. Head darkest on region corresponding to neurocranium, outlined by brain pigment seen by transparency. Dark spots randomly distributed over entire head, except region of levator operculi muscle. Distal margin of integument fold of opercular patch of odontodes darkly pigmented. Interopercular patch of odontodes lacking dark pigment. Fin rays outlined in dark coloration. Pelvic fin slightly pigmented only in large adults (64.5–70.0 mm SL). Caudal fin with broad longitudinal dark stripe from base of middle caudal-fin rays to nearly margin of fin. Caudal stripe more evident in young specimens (a pattern similar to that in T. immaculatus , T. ipatinga and T. tantalus ).

Remarks: Trichomycterus reinhardti was described from Miguel Burnier on the Rio Itabira , a tributary of the Rio das Velhas , São Francisco Basin, at Minas Gerais State, Brazil ( Eigenmann, 1918). Until recently, representatives of the species were known only from the São Franscisco and Rio Grande ( Rio Paraná Drainage) basins in Central Minas Gerais State. However, Katz et al. (2021) reported two specimens of T. reinhardti (MNRJ 21560) from a small stream in the Gualaxo do Sul River, a tributary of the Rio Doce , this being the first record of the species in the Rio Doce. As suggested by the authors, that population might have reached the Rio Doce by headwater capture, since its locality is close to the São Francisco Basin. The phenomenon is common and may explain the across-basin distribution of a number of other species in the Rio Doce (see Discussion).

Trichomycterus reinhardti is a particularly distinctive species, which until recently could not be confused with any other Trichomycterus . Starting with Alencar & Costa (2006), a number of species obviously close to T. reinhardti have been described in the past 15 years, such as T. pauciradiatus , T. septemradiatus , T. piratymbara , T. anaisae , T. sainthilairei , T. luetkeni , T. funebris , T. humboldti and T. ingaiensis (Alencar & Costa, 2006; Katz et al., 2013; Costa & Katz, 2021). All these species are from adjacent localities covering a continuous area of Central Minas Gerais State, with some of them from the same tributary of the São Francisco as the type locality of T. reinhardti ( Rio das Velhas ). Morphometric and meristic characters used to segregate these species usually overlap, so their identification is difficult without resorting to locality information. The specimens found in the Rio Doce were considered as T. reinhardti by Costa & Katz (2021). Examination of the same specimens and comparisons with the holotype made herein confirm that identification. The status of the nine T. reinhardti -like species described more recently still needs close scrutiny.

Geographic distribution: Trichomycterus reinhardti was described from the Rio Itabira , a tributary of Rio das Velhas , Minas Gerais and is also present in the Rio Doce on a stream tributary of the Gualaxo do Sul River, bordering the São Francisco Basin ( Fig. 34).

Type material examined: holotype FMNH 58081, 53.1 mm SL; Miguel Burnier, state of Minas Gerais, Brazil, Rio Itabira , tributary of Rio das Velhas ; col. J. Haseman, 14 May 1908.

Additional material studied: Brazil, state of Minas Gerais . MNRJ 21560 , 2 , 28.5–60.4 mm SL; south-east of the Ouro Preto-Ouro Branco road, small stream at deep ravine, Rio Doce Basin , 20°29’57”S 43°37’13”W; col. P.A. Buckup, A . T. Aranda , M . R.S. Melo , F.M. Costa & J.J. Vital, 22 November 2000 . MZUSP 109431 , 5 , 44.2– 68.3 mm SL, 1 c&s 55.8 mm SL; Ouro Preto, stream at the right border of Córrego das Almas, tributary of the Rio das Velhas , São Francisco Basin , 20°23’51”S 43°53’04”W; col. G. Padilha, 22 March 2011 . MZUSP 109371 , 3 , 59.4–64.2 mm SL; Caeté, Maquiné Creek, tributary of Ribeirão da Prata , tributary of Rio das Velhas , São Francisco Basin , 20°01’39”S 43°41’57”W; col. B. Maia, August 2010 . MZUSP 82366 , 2 , 49.3– 50.4 mm SL; Barbacena, Sapateiro Creek ; col. J.C. Oliveira, A.L. Alves, L . R. Sato , 12 October 2001 . MZUSP 90850 , 2 , 43.3–59.3 mm SL; Belo Horizonte , Parque das Manguabeiras, stream tributary of Rio das Velhas , São Francisco Basin; col. C.B.M. Alves, July 2002 .

TRICHOMYCTERUS TANTALUS SP. NOV. REIS, VIEIRA, DE PINNA

( FIGS 6, 35)

Z o o b a n k r e g i s t r a t i o n: u r n: l s i d: z o o b a n k. org:act: F805C7B2-84E0-4B9C-97D5-94A41A7D2731

Holotype: MZUSP 123369 , 76 mm SL; Brazil, state of Minas Gerais, Baguari , main stream of Rio Doce Basin (19°1’33.62”S 42°7’29.12”W); col. V. J. C. Reis & T. Pessali, 12 November 2017.

Paratypes: All from Brazil, state of Minas Gerais. MZUFV 2565 , 1, 154 mm SL; Raul Soares, Matipó River , downstream from UHE Emboque (20°7’25.71”S 42°23’6.07”W); col. J. Dergam, 27 August 1998. MZUSP 126759 , 23 , 68.4–80.2 mm SL, 2 (c&s) 64.6–80.3 mm SL; same data as holotype .

Diagnosis: The combination of a yellowish body colour with uniform dark colour concentrated on dorsum with a bifurcated caudal fin is unique to T. tantalus among all congeners. The combination of the following traits further distinguishes T. tantalus from congeners: (1) numerous opercular odontodes (25–33); (2) I + 8 pectoral-fin rays; (3) three lateral-line pores (vs. two); and (4) caudal fin bifurcated. Among congeners in south-eastern SouthAmerica, character 1 distinguishes T. tantalus from all except for T. barrocus , T. caipora , T. aff. caipora , T. immaculatus and T. lauryi ; character 2 from all except for T. astromycterus , T. caipora , T. giganteus , T. immaculatus , T. lauryi , T. nigricans ; character 3 from all except T. astromycterus , T. aff. caipora , T. ipatinga , T. nigricans and T. vinnulus ; and character 4 from all except for T. astromycterus . Among congeners in the Rio Doce Basin , T. tantalus is most similar to T. immaculatus . In addition to characters above, T. tantalus is further distinguished from T. immaculatus by the more numerous dentary teeth (13–15 vs. 9–12). The two species are separated by a barcoding distance of 3.8%.

Description: Morphometric data for specimens examined is presented in Table 15. 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 thin and abruptly expanding at base of caudal fin, caused by increase in length of dorsal and ventral procurrent caudal-fin rays.

Head approximately 1/5 of SL, pentagonal, slightly longer than wide and depressed. Mouth subterminal. Upper jaw longer than lower. Upper lip wider than lower lip and laterally continuous with base of maxillary barbel. Lower lip small, atrophied in many specimens from MZUSP 126759, approximately 1/2 width of upper one, partly divided into right and left portions by 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, 67–75 arranged in four irregular rows, first row with 13–15 teeth, extending from base to slightly up of 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 67–70 conical teeth arranged in four irregular rows, first row with approximately 11–15 teeth, over entire ventral surface of premaxilla.

Eye medium-sized, slightly protruding, positioned latero-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 tubular narrowing markedly towards fine tip, reaching from anterior border of eyes until anteromesial border of interopercle. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching from posterior border of posterior naris to posterior border of eyes, not touching the interopercle. Nasal barbel originating on posterolateral region of anterior naris, reaching from posterior border of posterior naris to slightly posterior to eyes. Interopercular patch of odontodes large compared to head length, 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. Interopercular odontodes arranged in three or four 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 40–52. Opercular patch of odontodes on dorsolateral surface of posterior part of head, positioned anterodorsally to pectoral-fin base, roundish in shape and large, 2 twice or more eye diameter in dorsal aspect of head. Opercular odontodes 25–33, 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 posterior and ventral to opercular patch of odontodes. Pectoral-fin rays I + 8. First pectoral-fin ray (unbranched) longest and prolonged as filament beyond fin margin. Other rays progressively less long, 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, slightly covering anal and urogenital openings in adults. Bases of pelvic fins positioned close to each other. Pelvic-fin rays I + 4, first ray unbranched. Anterior process of basipterygium long, hook-like and laterally curved. Dorsal fin long, its distal margin sinusoidal. Dorsal-fin origin closer to base of caudal fin than to tip of snout. Dorsal-fin rays iii + II + 7 (1) or iv + II + 7 (1). 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 iii + II + 5 or iv + II + 5. Caudal fin bifurcated, 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 36 (2). First dorsal-fin pterygiophore immediately anterior to neural spine of 16 th (1) or 17 th (1) vertebra, first anal-fin pterygiophore immediately anterior to neural spine of 21 st (1) or 22 nd (1) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally extending until 1/4 on caudal-fin rays. Procurrent caudal-fin rays, 16–17 dorsally and 13–14 ventrally, beginning anteriorly at 32 nd vertebrae. Ribs 11 (1) or 12 (1). Branchiostegal rays 7 (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 single s6 posteromedial to eye and at midlength of frontal. Infraorbital latero-sensory canal incomplete with four pores, i1 and i3 anteriorly and i10 and i11 posteriorly. This canal extending from sphenotic posteriorly to terminal pore located ventroposteriorly to eye. Infraorbital pore i1 located ventrolateral to nasal-barbel base and autopalatine, i3 ventrolateral 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, ll2 and ll3 present dorsomedial to pectoral-fin base.

Coloration in ethanol: Yellowish body with dark chromatophores homogeneously distributed not f o r m i n g m a c u l a e. D a r k p i g m e n t a t i o n v a r y i n g interspecifically from body totally darkly pigmented, except to ventral region (rare), to dark covering uniformly distributed dorsally from head to posterior end of caudal peduncle, laterally reaching mid-lateral line and abruptly ending ventral to that. Head darkest on region corresponding to neurocranium, outlined by brain pigment. Cheeks less heavily pigmented than neurocranium over area of dilatactor perculi muscle. Base of nasal barbels surrounded with concentration of dark pigment, extending posteriorly as elongate dark field to anterior margin of eyes. Distal margin of integument fold of opercular patch of odontodes darkly pigmented. Interopercular patch of odontodes white. Ventral side of the body lacking dark pigment. Base of pectoral and dorsal fins darkly pigmented. Caudal fin with broad longitudinal dark stripe from base of middle caudal-fin rays to nearly margin of fin.

Etymology: From the Ancient Greek mythological figure Τάνταλος (Tantalos), who was eternally tormented in the underworld, the word ‘ tantalus ’ going on to refer to acts of torment in Latin and other languages. The name is chosen for the hypertrophied opercular patch of odontodes in this species, the largest among species of Trichomycterus in the Rio Doce Basin.

Remarks: Trichomycterus tantalus is a distinctive species, not only in the Rio Doce , but across the south-eastern Brazilian region. This is a rheophilic species, found so far only in the main channel of the Rio Doce and the main channel of the Rio Matipó. In both cases, specimens were collected near hydropower plants during fish transposition activities. The species has obvious rheophilic characters such as a bifurcated caudal fin ( Lujan & Conway, 2015; Zanata et al., 2020). Its extremely tough, resilient integument is also suggestive of an adaptation to withstand attrition among boulders in strong currents. Numerous specimens of T. tantalus display severe head abnormalities, such as deformed and asymmetrical metapterygoids, quadrate and autopalatines, bent mesethmoid and other deformities in anterior cranial bones. These abnormalities are perhaps caused by repeated trauma and subsequent healing in their turbulent habitat, where specimens supposedly collide often with rocks, causing osseous damage and growth aberrations. Interestingly, other species collected syntopically with T. tantalus , such as T. immaculatus , do not show such skeletal alterations.

Although it differs markedly morphologically from congeners in the Rio Doce Basin , T. tantalus differs relatively little in barcoding data from T. ipatinga (1.8%) and T. melanopygius (1.5%). Such low genetic distances among morphologically distinct species is a common phenomenon among Neotropical freshwater fishes (see Discussion below and Perdices et al., 2002, 2005; Montoya-Burgos, 2003; Hubert et al., 2007; Ornelas-Gacia et al., 2008; Costa-Silva et al., 2015). In the phylogenetic hypothesis ( Fig. 1), all samples referable to T. tantalus cluster in a clade. The species is included in a group with T. aff. caipora , T. ipatinga and T. melanopygius , but its sister group is unresolved. Also, despite a normal degree of intraspecific morphological variation, T. tantalus displays low intraspecific DNA barcoding divergence (> 0.2%). The recently described Trichomycterus largoperculatus Costa & Katz, 1922 (Zoosyst. Evol. 98, 13–21) from the Rio Paraíba do Sul, is probably closely related to T. tantalus . The two species share a caudal fin bilobed with pointed corners, nine pectoral-fin rays, a single s6 pore, and a vertical dark band across the base of the caudal fin. They differ in the number of lateral-line pores (two in T. largoperculatus and three in T. tantalus ); and in the number opercular and interopercular odontodes respectively (48–62, 92–100 in T. largoperculatus , vs. 25–33, 40–52 in T. tantalus ).

Geographical distribution: Trichomycterus tantalus occurs in the middle sectors of the main channel of the Rio Doce and in the main channel of the Matipó River ( Fig. 36).