Trichomycterus barrocus, 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 : 380-384

TRICHOMYCTERUS BARROCUS SP. NOV.

( FIG. 17)

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: 2D2A53D8-7B5A-40BE-9373-D644C86DCEC4

Holotype: MBML 14092, 79.8 mm SL; Brazil, Espírito Santo, Afonso Cláudio, Boa Sorte River, Guandu River (20°10’57.00”S 41°4’50.00”W); col. L.M. Sarmento-Soares, R. F. Martins-Pinheiro, A. T. Aranda, R. L. Teixeira, M.M.C. Roldi & M.M. Lopes, 12 June 2009.

Paratypes: MBML 14093, 2, 54.9–79.8 mm SL, 1 c&s, 55.86 mm SL; Brazil, Espírito Santo, Afonso Cláudio, Boa Sorte River, Guandu River , (20°10’57.00”S 41°4’50.00”W); col. L.M. Sarmento-Soares, R. F. Martins-Pinheiro, A. T. Aranda, R. L. Teixeira, M.M.C. Roldi & M.M. Lopes, 12 June 2009. MZUSP 126763 , 1 , 66.7 mm SL, collected together with holotype .

Diagnosis: The combination of the following traits distinguishes T. barrocus from congeners: (1) colour pattern composed of dark maculae forming two thick longitudinal stripes (interrupted or continuous), one mid-dorsal and one mid-lateral; (2) barbels short, nasal barbel barely crossing the anterior border of eyes, maxillary and rictal barbels not reaching the interopercle (vs. long barbels surpassing posterior margin of eyes and reaching interopercle); (3) I + 7 pectoral-fin rays (vs. I + 5, I + 6 or I + 8); (4) two lateral line pores (vs. three or more). Among species of Trichomycterus in south-eastern South America, character 1 distinguishes T. barrocus from all congeners except some colour morphs of T. alternatus , T. caipora , T. aff. caipora , T. giganteus , T. itatiayae Miranda Ribeiro 1906 , T. nigroauratus Barbosa & Costa, 2008 and T. reinhardti (Eigenmann, 1917) ; character 2 distinguishes T. barrocus from all congeners except some morphs of T. alternatus , T. astromycterus , T. caipora and T. aff. caipora ; character 3 from the entire T. brasiliensis and T. reinhardti species complex ( Barbosa & Costa, 2010; Costa, 2021; Costa & Katz, 2021), plus T. trefauti (all with I + 6 or fewer) and from T. astromycterus , T. giganteus , T. immaculatus , T. lauryi , T. nigricans , T. pradensis and T. tantalus (all with I + 8 or more); character 4 distinguishes T. barrocus from T. astromycterus , T. caipora , T. aff. caipora , T. ipatinga , T. nigricans , T. tantalus and T. vinnulus . Among congeners in the Rio Doce Basin , T. barrocus is most similar to T. alternatus and T. aff. caipora . The species is further distinguished from T. alternatus by the absence of a large fenestra between the orbitosphenoid and the frontal (vs. presence), deeper body (9.0–13.9% SL vs. 18.3–13.8%), shorter pre-anal length (49–69% SL vs. 63.8–82.9%) and shorter prepelvic length (41.9–52.5% SL vs. 52.8– 70.9%). It is further distinguished from T. aff. caipora by the larger eye (14.8–17.5% SL vs. 12.2–14.4%) and by having seven branchiostegal rays (vs. six).

Description: Morphometric data is presented inTable 6. Body long and almost 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 long and less deep than body at end of anal-fin base.

Head approximately 1/5 of SL, pentagonal, longer than wide and depressed. Mouth subterminal. Upper jaw slightly longer than lower jaw. 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, arranged in four irregular rows, first row with 12 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 teeth arranged irregularly in four rows, first row with approximately 13 teeth, over entire ventral surface of premaxilla. Premaxillary teeth conical.

Eye medium sized, slightly 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, barely reaching vertical through posterior border of eye. Rictal barbel inserted immediately ventral to maxillary barbel, its tip reaching until vertically posterior border of eye, not reaching the interopercle. Nasal barbel originating on posterolateral region of anterior naris, minimally reaching posterior margin of eye, but not interopercle. 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 opercular patch of odontodes. 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 38–49. 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 15–25, 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 + 7. First pectoral-fin ray (unbranched) longest, prolonged as filament beyond fin margin. 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, slightly covering anal and urogenital openings in adults. Base of pelvic fins positioned close to each other. Pelvic-fin rays I + 4. Anterior processes of basipterygium girdle short 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 + 6 (1) or iii + 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 + I + 7 (1) or iii + II + 5 (2). Caudal fin subtruncated, 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 (3) or 37 (1). First dorsal-fin pterygiophore immediately anterior to neural spine of 16 th (1), 17 th (1) or 18 th (1) vertebra, first anal-fin pterygiophore immediately anterior to neural spine of 21 st (2) or 22 nd (1) vertebra. Caudal-fin procurrent rays plus one segmented non-principal ray dorsally and ventrally. Procurrent caudal-fin rays, 15–17 dorsally and 12–13 ventrally, beginning anteriorly at 31 st (1), 32 nd (1) or 33 rd (1) vertebrae. Ribs 11 (1), 12 (1) or 13 (1). Branchiostegal rays 7 (3). Dorsal-fin pterygiophores 7 (1) or 8 (2). Anal-fin pterygiophores 6 (3).

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 close to each other, 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 and ll2 dorsomedial to pectoral-fin base.

Coloration in ethanol: Body with two partially unfused rows of dark maculae. First row forming broad stripe along mid-dorsum of trunk from posterior margin of head to caudal fin, merged with amorphous dark maculae resembling drops of dark ink on a white background. Second row formed by large and round dark maculae along lateral midline from end of opercle to base of caudal fin, forming broad continuous stripe in some specimens. Small round or irregular dark maculae ventral to second row, from middle of body to caudal fin. Ventral part of the body with no dark pigmentation. Head with partly amalgamated brownish chromatophores.Tip of snout (from anterior naris to tip of upper lip), cheeks (to ventral margin of orbits) and region ventroposterior to eye (excluding portion anterior to opercle) with little or no dark pigment. Integument of opercular patch of odontodes darkly pigmented. Interopercular patch of odontodes with no pigmentation. Pectoral, pelvic, dorsal and anal fins with brownish spots mainly along their bases. Caudal fin with vertical dark stripe across base and spots amongst rays.

Etymology: The epithet is a Latinized adjective from Portuguese barroco, originally designating a pearl of irregular shape, here referring to the the baroquestyle beauty of this species.

Remarks: Trichomycterus barrocus is a distinctive and readily diagnosable species, endemic to the Lower Rio Doce Basin. Some meristic values in this species are variable (number of post-Weberian vertebrae, position of first dorsal and ventral pterygiophores relative to vertebral column, number of ribs and anal-fin rays; cf. Description above). Despite such variation observed in only three specimens available for osteological examination, they fall in the range of variation seen in species of Trichomycterus represented by more abundant material. Because other diagnostic characters do not vary significantly, it seems likely that the type material represents a single species. The highly distinctive colour pattern of T. barrocus distinguishes it from all congeners. The dorsal colour pattern, in particular, has no parallel in the genus. The mid-lateral colour pattern vaguely resembles some species such as T. reinhardti (Eigenmann, 1917) , some colour morphs of T. alternatus , T. itatiayae Miranda Ribeiro, 1906 , T. giganteus , T. nigroauratus Barbosa & Costa, 2008 and some colour morphs of T. aff. caipora . However, in addition to the diagnostic characters listed above, in all of those the colour pattern is immediately distinguishable from that of T. barrocus . No material suitable for sequence analysis is currenly available of the species.

Geographical distribution: Trichomycterus barrocus is endemic to the Lower Rio Doce Basin , at the Boa Sorte River, a tributary of Rio Guandu ( Fig. 18).

384 V. REIS and M. DE PINNA