Trichomycterus argos, LEZAMA ET AL., 2012

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 : 372-374

TRICHOMYCTERUS ARGOS LEZAMA ET AL., 2012

( FIG. 5)

Trichomycterus argos Lezama, Triques & Santos, 2012: 62 , figs 2, 3a [type locality: Parque Estadual da Serra do Brigadeiro, Córrego Nova, headwaters of the Rio Casca , right bank tributary of Rio Doce at the limits of Rio Doce and Rio Paraíba do Sul basins, 20°43’19”S 42°28’43”W, Minas Gerais State, Brazil; holotype: AZUFMG 103, paratypes: DZUFMG 058 (1), 059 (14), 067 (1, c&s); MZUSP 106274 (3)]; DoNascimiento et al., 2014b: 724 (comparison); García-Melo et al., 2016: 237 (citation, relationships); Donin et al., 2020: 3 (comparison); Reis et al., 2020: 2 (diversity); DoNascimiento & Prada-Pedreros, 2020: 978 (comparison).

Diagnosis: The combination of the following traits distinguishes T. argos from congeners: (1) pectoral-fin rays I + 6, (vs. I + 5, I + 7 or I + 8); (2) colour pattern composed of irregular round, vermiculate or reticulate maculae randomly distributed over most of body; (3) suture line between parietosupraoccipital and frontal bones straight and oriented orthogonally to longitudinal body axis (vs. irregular and oblique) ( Lezama et al., 2012: fig. 3a); (4) large foramen for ramus lateralis accessorius facialis nerve on parietosupraoccipital, visible in dorsal view ( Lezama et al., 2012: fig. 3) (vs. foramen minute, hardly visible in dorsal view). Among congeners in south-eastern South America, character 1 distinguishes T. argos from all congeners except Trichomycterus pirabitira Barbosa & Azevedo 2012 , T. itatiayae , T. trefauti , those in the T. reinhardti species complex ( Costa & Katz, 2021), except from Trichomycterus humboldti Costa & Katz 2021 , Trichomycterus pauciradiatus Alencar & Costa 2006 , Trichomycterus piratymbara Katz, Barbosa & Costa, 2013 and Trichomycterus sainthilairei Katz & Costa, 2021 and those in the T. brasiliensis species complex ( Barbosa & Costa, 2010); character 2 from all congeners except those in the T. brasiliensis species complex, plus T. lauryi and T. pirabitira ; characters 3 and 4 each distinguishes T. argos from species in the T. brasiliensis species complex. Among congeners in the Rio Doce Basin , T. argos is most similar to T. brunoi . In addition to characters above, T. argos can be further distinguished from T. brunoi by the longer snout (41.9–45.9% vs. 28.0–41.2%), the longer prepelvic length (59.5–60.6% vs. 41.4–58.5%) and the more numerous interopercular odontodes (39–40 vs. 26–31).

Description: Morphometric data for specimens examined is presented in Table 4. Body long and almost totally straight, trunk roughly round in cross-section near head, then slightly deeper than wide 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 from beginning of anal-fin base to slightly at the base of caudal-fin rays.

Head approximately 1/5 to 1/4 of SL, pentagonal, longer than wide and depressed, with a long snout. 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 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, 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 teeth arranged irregularly in four rows over entire ventral surface of premaxilla. Premaxillary teeth conical.

Eye small, 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 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 base of pectoral fin. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching lateroposterior border of interopercle. Nasal barbel originating on posterolateral region of anterior naris, reaching from slightly anterior to anterior border of opercle to touching, but not surpassing, anterior border of opercle. Interopercular patch of odontodes, 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. Odontodes arranged in 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 39–40. Opercular patch of odontodes on dorsolateral surface of posterior part of head, positioned anterodorsally to pectoral-fin base, roundish in shape slightly smaller than eye in dorsal aspect of head. Opercular odontodes 14–18, sunk in individual slits of integument, progressively larger posteriorly, all with fine tips, with largest ones curved distally and claw-like. Entire opercular patch surrounded by rim of integument.

Pectoralfininsertedimmediatelyposteriorandventral to opercular patch of odontodes. Pectoral-fin rays I + 6. First pectoral-fin ray (unbranched) longe, prolonged as filament beyond fin margin, with short filament. Other rays progressively shorter, their tips following continuous line along fin margin. Pelvic fin with convex distal profile, its origin slightly posterior to middle of SL and anterior to vertical through dorsal-fin origin, surpassing anal and urogenital openings in adults. Pelvic-fin rays I + 4, fin bases close to each other. 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 + 7. 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 + 5. Caudal fin rounded 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 39 (1). First dorsal-fin pterygiophore immediately anterior to neural spine of 20 th (1) vertebra, first anal-fin pterygiophore immediately anterior to neural spine 23 rd (1) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally. Procurrent caudal-fin rays, 20 dorsally and 15 ventrally, beginning anteriorly at 33 rd to 35 th vertebrae, respectively. Ribs 14 (1). Branchiostegal rays 8 (1). 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, paired s6, posteromedial to eye and at midlength of frontal, as distant from the orbits as from the mesial line. Infraorbital laterosensory canal incomplete with four pores, i1 and i2 anteriorly and i10 and i11 posteriorly. This canal extending from sphenotic posteriorly to terminal pore located ventroposteriorly to eye. Canal lacking associated ossification. 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 argos has two basic types of pigmentation patterns, probably associated with ontogeny. Contrary to original description, a small paratype of this species ( Fig. 5 A-C) has chromatophores forming round dark maculae bigger than eye diameter disposed in a row along mid-lateral portion of body begining immediately posterior to opercle and extending to end of dorsal-fin base. Mid-lateral line maculae faint or entirely absent in large specimens (90.8 mm SL). In both small and large paratypes dorsally to mid-lateral line, several smaller, round to amoeboid dark blurred maculae, coalescent or not. Maculae or spots randomly distributed dorsally on trunk. Ventrally to mid-lateral line, round dark maculae randomly distributed, fewer and larger than dorsal maculae. Caudal peduncle with fewer chromatophores than rest of body. Few or no dark pigmentation ventrally on abdomen. Fins with few or no dark pigment, except for vertical dark bar at base of caudal fin. Mid-dorsum with dark chromatophores forming small round to amoeboid blurred and partly coalescent maculae. Concentration of chromatophores on entire body increasing with size of specimens. Head with numerous dark round, variably-sized, widelyspaced maculae laterally in small specimens. In the larger specimen vermiculate to amoeboid maculae lateral on head. Tip of snout, cheeks and region ventroposterior to eye with fewer chromatophores than remainder of head. Region surrounding opercular odontodes darkly pigmented, most concentrated on surrounding integument fold. Region surrounding interopercular odontodes without dark pigmentation.

Remarks: Trichomycterus argos clearly fits the so-called Trichomycterus brasiliensis complex ( Bockmann & Sazima, 2004; Barbosa & Costa, 2010), sharing characters such as I + 6 pectoral-fin rays, a similar colour pattern and closely-set pelvic-fin bases. Its presumably close relative, T. brunoi Barbosa & Costa, 2010 , is already in that complex and the two species are the only taxa resembling T. brasiliensis so far known to occur in the Rio Doce. Trichomycterus brasiliensis itself has never been recorded from the Rio Doce basin. A lot from Piranga basin (MNRJ 789) includes two specimens closely resembling T. brasiliensis . Due to entanglements in the taxonomy of that species complex ( Barbosa & Costa, 2010), with 14 very similar nominal species, and because there are only two old specimens, additional material and analyses are needed in order to confirm their identity.

Lezama et al. (2012) reported that T. argos is distinguished from T. brunoi exclusively by its colour pattern (presence of stripes, vermiculations or reticulations in the former and their absence in the latter). However, within samples examined referable to the two species, the ranges of coloration variation clearly overlap, thus blurring the apparent limits between the two taxa ( Figs 5, 12). Indeed, colour pattern has been reported to vary considerably within species of the T. brasiliensis species complex ( Barbosa & Costa, 2010). Despite that, the two species can be distinguished by additional phenotypic evidence as listed in the diagnosis. Their divergence is small and T. argos and T. brunoi are clearly close relatives, an inference further strengthened by the proximity of their respective type localities, only c. 50 km distant in straight line, with many small tributaries between them ( Fig. 13).

Geographical distribution: Trichomycterus argos is known only from the type material, collected in the Rio Casca , a tributary of Rio Doce Basin in the Serra do Brigadeiro State Park ( Fig. 13).

Type material examined: MZUSP 106274, 3, 56.1– 90.8 mm SL, 1 c&s 69.5 mm SL, paratypes, Brazil, state of Minas Gerais, Araponga Municipality, Parque Estadual da Serra do Brigadeiro, Córrego Serra Nova, headwaters of the Rio Casca , right bank tributary of Rio Doce at limit of Rio Doce and Rio Paraíba do Sul basins (20°43’19”S 42°28’43”W), col. P.S. Santos, 7 October 2001.