Trichomycterus vinnulus, Reis & Pinna, 2023

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 : 424-427

TRICHOMYCTERUS VINNULUS SP. NOV.

( FIG. 10, 37)

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: 68036FCA-384B-4449-8FBA-626C38B445E1

Holotype: MZUSP 123750, 54.0 mm SL; Brazil, state of Minas Gerais, Rio Doce Municipality, Córrego dos Borges Creek running into left margin of the reservoir and the Rio do Peixe River, Risoleta Neves Hydroelectric Dam (20°12’21.63”S 42°52’56.24”W); col. V. J.C. Reis, M. de Pinna, G. Ballen, G. F. de Pinna, 24 June 2018.

Paratypes: MZUSP 126760, 43, 28.8–60.7 mm SL; same data as holotype; MZUSP 123757, 7, 32.3–59.3 mm SL; Rio Doce Municipality , Rio do Peixe, Rio Piranga Basin (left-margin tributary of Rio Doce , downstream from the Risoleta Neves reservoir) (20°11’40”32”S 42°51’8”47”W); col. V.J.C. Reis, M. de Pinna, G. Ballen, G.F. de Pinna, 24 June 2018.

Diagnosis: The combination of the following traits distinguishes T. vinnulus from other Trichomycterus species: (1) numerous round dark maculae randomly distributed throughout body; (2) pectoral fin rays I + 7 (vs. I + 5, I + 6 or I + 8); and (3) three lateral-line pores (vs. two). Among congeners in south-eastern South America, character 1 distinguishes T. vinnulus from all except some colour morphs of T. brasiliensis , T. ipatinga and T. laury ; character 2 distinguishes T. vinnulus from all species in the T. brasiliensis and T. reinhardti species complexes ( 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 from all except T. astromycterus , T. aff. caipora , T. ipatinga , T. nigricans and T. tantalus . Among congeners in the Rio Doce Basin , T. vinnulus is most similar to T. ipatinga and T. alternatus . In addition to the characters above, T. vinnulus can be further distinguished from T. ipatinga by having fewer premaxillary teeth on first row (8 vs. 10–14); and by number of interopercular odontodes (25–26 vs. 25–38). Trichomycterus vinnulus can be further distinguished from T. alternatus by number of lateral line pores (3 vs. 2); colour pattern consisting of numerous round maculae randomly distributed through the body (vs. round maculae anteroposteriorly distributed in four rows in each side of body).

Description: Morphometric data for specimens examined is presented in Table 16. Body long and almost straight in lateral aspect, 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 long, as deep as body and slightly expanding at caudal-fin base.

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, 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, 35–46 arranged in four irregular rows, first row with 9–11 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 36–40 teeth arranged irregularly in four rows, first row with approximately 9–13 teeth, over entire ventral surface of premaxilla. Premaxillary teeth conical.

Eye large sized, slightly protruding, positioned laterodorsally 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 base of pectoral fin. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching from posterior border of posterior naris to anteromesial border of interopercle. Nasal barbel originating on posterolateral region of anterior naris, reaching posterior margin of eyes or slightly beyond, never reaching opercular patch of odontodes. Interopercular patch of odontodes small 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 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 25–26. Opercular patch of odontodes on dorsolateral surface of posterior part of head, positioned anterodorsally to pectoral-fin base, roundish in shape and small, smaller than eye diameter in dorsal aspect of head. Opercular odontodes 11–14, 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 ventroposterior to opercular patch of odontodes. Pectoral-fin rays I + 7. First pectoral-fin ray (unbranched) slightly longer than remaining in rays, prolonged as filament beyond fin margin. Other rays progressively less long, 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, covering anal and urogenital openings in adults. Base of pelvic fins separated from each other by one eye diameter. Pelvic-fin rays I + 4. 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 or iv + 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 + II + 5 or iii + II + 5. Caudal fin subtruncate, with 6 + 7 principal rays. Adipose fin absent or modified into low integument fold extending between end of dorsal fin and caudal-fin origin. Post-Weberian vertebrae 36 (1) or 37 (1). 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 20 th (1) or 21 st (1) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally extending until ¼ on caudal-fin rays. Procurrent caudal-fin rays, 19–21 dorsally and 12 or 13 ventrally, beginning anteriorly at 32 nd vertebrae. Ribs 9 (1) or 12 (2). Branchiostegal rays 7 (3). 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. 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 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: Trichomycetus vinnulus has a wide range of colour patterns between two extreme morphs. One colour morph consists of round dark maculae organized in four longitudinal rows. The size, shape and number of maculae vary among specimens, with bigger, round and less numerous (minimum 11 in the mid-line) maculae in young specimens. First row along mid-dorsal line from occiput, through entire dorsum, into dorsal edge of caudal peduncle and to base of caudal fin. Second row ventrolateral to that, extending from base of head through upper part of flanks, dorsal portion of caudal peduncle, to base of caudal fin. Third row running along mid-lateral line, from immediately posterior to opercle to base of caudal fin. Fourth and ventralmost row shorter, extending from anterior region of abdomen through ventral margin of caudal peduncle to base of caudal fin. Fourth row usually composed of unaligned maculae. Rows mostly independent, rarely fusing. Another colour morph, common in adults, has the entire body (except for ventral region), covered with dark amorphous maculae, smaller than eye diameter. Head entirely covered by small dark spots or with dark blotches probably resulting from fusion of smaller maculae. Head darkest on region corresponding to neurocranium, outlined by brain pigment. Cheeks over protractor uencan muscle region less heavily pigmented than uencanem. Base of nasal barbels surrounded with concentration of dark pigment, extending posteriorly as elongate dark field to anterior margin of eyes. Distal margin of integumentary fold of opercular patch of odontodes darkly pigmented. Interopercular patch of odontodes white. Ventral side of the body lacking dark pigment. Fin rays covered with small dark spots.

Etymology: From the Latin adjective vinnulus , delightful, often used to refer to wine.

Remarks: Trichomycterus vinnulus is a distinctive and readily diagnosable species. However, DNA barcoding shows relatively low divergence relative to its sympatric species T. alternatus , 1.9% and T. astromycterus , 2% ( Table 2). Barcoding divergence values found among T. vinnulus , T. alternatus and T. astromycterus are low when compared with other divergence values for Trichomycterus reported here and in previous works ( Pereira et al., 2013; Sales et al., 2018). However, Ward et al. (2009) estimated that specimens with 2% barcoding divergence have a> 95% probability to belong to different species. Low genetic distance among morphologically distinct Neotropical freshwater fish species can be explained by many factors, including recent speciation, mitochondrial introgression due to hybridization and also incomplete lineage sorting ( Montoya-Burgos, 2003; Hubert et al., 2007; Perdices et al., 2002, 2005; Ornelas-Gacia et al., 2008; Costa-Silva et al., 2015).

Trichomycterus vinnulus co-inhabits the same creek and was collected in the same microhabitat with T. alternatus and T. astromycterus . Therefore, the possibilityofmitochondrialintrogressionbyhybridization is plausible. Similar situations were reported in various other fish groups, for example Mobula alfredi (Krefft, 1868) vs. Mobula birostris (Walbaum, 1792) ( Kashiwagi et al., 2012) and Rineloricaria langei Ingenito et al. 2008 vs. Rineloricaria kronei (Miranda Ribeiro, 1911) ( Costa-Silva et al., 2015) . In the present case, analyses using nuclear DNA markers would be necessary to determine the reasons for low barcode divergence in association with pronounced phenotypic divergence among T. vinnulus , T. alternatus and T. astromycterus . However, T. vinnulus differs from its congeners by phenotypic divergence as large as, or larger than, normally seen among other Trichomycterus species in the T. alternatus clade and even in the whole genus.