Trichomycterus largoperculatus, Costa & Katz, 2022

Costa, Wilson J. E. M. & Katz, Axel M., 2022, A new catfish of the genus Trichomycterus from the Rio Paraiba do Sul Basin, south-eastern Brazil, a supposedly migrating species (Siluriformes, Trichomycteridae), Zoosystematics and Evolution 98 (1), pp. 13-21 : 13

publication ID	https://dx.doi.org/10.3897/zse.98.72392
publication LSID	lsid:zoobank.org:pub:42902D76-51B9-449A-8A41-8E548B13C2AD
persistent identifier	https://treatment.plazi.org/id/A5F16812-88EC-49FA-92CC-78E85C176A86
taxon LSID	lsid:zoobank.org:act:A5F16812-88EC-49FA-92CC-78E85C176A86
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Trichomycterus largoperculatus
status	sp. nov.

Treatment

Trichomycterus largoperculatus sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Holotype.

UFRJ 6987, 77.8 mm SL; Brazil: Estado do Rio de Janeiro: Município de Além Paraíba: Rio Paraíba do Sul just below Ilha dos Pombos Dam, 21°50'36"S, 42°34'46"W, about 105 m a.s.l.; L. P. Bastos, 10 March 2009.

Paratypes.

UFRJ 6988, 7, 35.2-91.5 mm SL; UFRJ 6989, 3 (C&S), 55.7-46.2 mm SL; CICCAA 02695, 2, 50.7-51.3 mm SL; all collected with holotype.

Diagnosis.

Trichomycterus largoperculatus is distinguished from all species of Trichomycterus s.s. by having more opercular odontodes (48-62 vs. 11-31), more interopercular odontodes (92-100 vs. 23-72) and a unique colour pattern consisting of a dark brown flank with a longitudinal pale yellow stripe on its dorsal portion (vs. never a similar colour pattern) and the presence of a black bar on the basal portion of the caudal fin (vs. absence).

Description.

Morphometric data are in Table 1 View Table 1 . Body moderately slender, subcylindrical and slightly depressed anteriorly, compressed posteriorly. Greatest body depth at vertical just anterior to pelvic fin base. Dorsal profile of head and trunk slightly convex, approximately straight on caudal peduncle; ventral profile straight to slightly convex between lower jaw and end of anal-fin base, straight on caudal peduncle. Anus and urogenital papilla at vertical through middle portion of dorsal-fin base. Head trapezoidal in dorsal view. Anterior profile of snout slightly convex in dorsal view. Eye relatively large, dorsally positioned in head. Minute skin papillae on ventral surface of head. Posterior nostril located nearer anterior nostril than orbital rim. Tip of maxillary and rictal barbels reaching anterior part of interopercular patch of odontodes; tip of nasal barbel reaching posterior part of orbit. Mouth subterminal. Jaw teeth pointed; premaxillary teeth 55-58, slightly curved, arranged in 5 irregular rows; dentary teeth 53-56, slightly curved backwards, irregularly arranged, more concentrated near symphysis. Branchial membrane attached to isthmus only at its anterior point. Branchiostegal rays 7.

Dorsal and anal fins subtriangular; total dorsal-fin rays 13 (iv + II + 7), total anal-fin rays 11 (iv + II + 5); anal-fin origin posterior to dorsal-fin base. Dorsal-fin origin at vertical through centrum of 16th or 17th vertebra; anal-fin origin at vertical between centrum of 22nd or 23rd vertebra. Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in filament, its length about 20% of pectoral-fin length without filament; total pectoral-fin rays 9 (I + 8). Pelvic fin truncate, its posterior extremity reaching urogenital papilla; pelvic-fin bases medially separated by interspace about half-length pelvic-fin base; total pelvic-fin rays 5 (I + 4). Caudal fin emarginated, upper and lower corners rounded to slightly pointed; total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 18-22 (xvii-xxi + I), total ventral procurrent rays 14-16 (xiii-xv + I). Vertebrae 35 or 36. Ribs 11 or 12. Two dorsal hypural plates, corresponding to hypurals 4 + 5 and 3, respectively; single ventral hypural plate corresponding to hypurals 1 and 2 and parhypural.

Laterosensory system (Fig. 2 View Figure 2 ). Supraorbital sensory canal continuous, posteriorly connected to posterior section of infra-orbital canal. Supra-orbital sensory canal with 2 paired pores, s1, adjacent to medial margin of anterior nostril and s3, adjacent and just posterior to medial margin of posterior nostril; supra-orbital pore s6 single, on centre of head, at transverse line through posterior half of orbit. Infra-orbital sensory canal arranged in 2 segments, each with two pores; anterior segment with pore i1, at transverse line through anterior nostril and pore i3, at transverse line just anterior to posterior nostril; posterior segment with pore i10, adjacent to ventral margin of orbit and pore i11, posterior to orbit. Postorbital canal with 2 pores: po1, at vertical line above posterior portion of interopercular patch of odontodes and po2, at vertical line above posterior portion of opercular patch of odontodes. Lateral line of body short, with 2 pores, posterior-most pore at vertical just posterior to pectoral-fin base.

Mesethmoidal region and adjacent structures (Fig. 4A View Figure 4 ). Anterior margin of mesethmoid nearly straight, mesethmoid cornu robust, subcylindrical, tip rounded. Antorbital and sesamoid supra-orbital narrow, rod-like, sesamoid supra-orbital longer, its length about 2.5 times antorbital length. Premaxilla sub-rectangular in dorsal view. Maxilla boomerang-shaped, slender, about equal premaxilla in length, slightly curved, with minute posterior process. Autopalatine sub-rectangular in dorsal view when excluding posterolateral process, narrow, its shortest width about half autopalatine length, lateral and medial margins slightly concave; latero-posterior process of autopalatine subtriangular, long, its length about two thirds of autopalatine length.

Jaw suspensorium and opercular apparatus (Fig. 4B View Figure 4 ). Metapterygoid trapezoidal, slightly longer than deep. Quadrate robust, dorsoposterior outgrowth continuous to hyomandibular outgrowth. Hyomandibula long, anterior outgrow shallow, slightly concave; postero-dorsal process of hyomandibula pointed. Opercle robust; opercular odontodes 48-62; odontodes pointed, arranged in irregular transverse rows; odontode patch depth about half opercle length; dorsal process of opercle short and blunt, about 2.5 times interopercular odontode patch length. Interopercle long, about three fourths hyomandibula length, with 92-100 odontodes; odontodes pointed, arranged in irregular longitudinal rows; dorsal interopercular process with deep anterior concavity. Pre-opercle compact, with expanded ventral flap.

Branchial arches (Fig. 4C View Figure 4 ). Basibranchial 2 and 3 subcylindrical, approximately equal in length, basibranchial 2 wider anteriorly; basibranchial 4 cartilage sub-pentagonal, longer than wide. Hypobranchial 1 subcylindrical, slightly widening at its distal tip; hypobranchial 2 and 3 subtriangular, anterior portion well-ossified. Ceratobranchial 1 broad in its proximal portion, gradually narrowing to its distal tip; ceratobranchials 2 and 3 widened in their middle portion, ceratobranchial 3 with deep concavity on posterior margin of basal portion; ceratobranchial 4 sub-rectangular, slightly narrowing proximally; accessory cartilage of ceratobranchial 4 minute; ceratobranchial 5 sub-rectangular, slightly curved, narrower than ceratobranchial 4; medial-proximal portion of ceratobranchial 5 bearing 24-26 small, slightly curved, conical teeth. Epibranchial 1 slender, with well-developed anterior uncinate process and minute posterior process; epibranchial 2 slender, with rudimentary anterior uncinate process; epibranchial 3 slender, with well developed, curved posterior uncinate process; epibranchial 4 broad, sub-rectangular. Pharyngobranchial 3 short, subcylindrical; pharyngobranchial 4 long, bearing broad dentigerous plate with 22-28 fang-shaped teeth.

Colouration in alcohol.

Flank dark brown with longitudinal pale yellow stripe on dorsal portion, ventral portion yellowish white; in juveniles and most adult specimens (Fig. 3B View Figure 3 ), highly contrasting dark and lighter flank zones; in some specimens, including holotype (Fig. 1 View Figure 1 ), dark zone paler and not expanding on venter and on pale yellow stripe, in some others, dark zone intensively pigmented, pale yellow stripe faint (Fig. 3A View Figure 3 ). Dorsal surface of head and trunk brown, ventral surface yellowish-white. Side of head brown, with unpigmented area on cheek at vertical line just anterior to orbit; dark chromatophores more concentrated between and around nostrils. Maxillary and rictal barbels pale yellow, nasal barbel pale yellow, posterior margin dark brown. Opercular and interopercular patches of odontodes pale yellow, posterior margin of opercle dark grey to black. Unpaired fins yellowish-white; dark brown chromatophores concentrated on basal portion of dorsal fin, forming diffuse brown area; horizontally elongated brown spot on caudal fin base and black bar on basal portion, almost inconspicuous in some specimens. Paired fins pale yellow, basal portion of pectoral fin dark brown.

Colouration in life.

Not recorded.

Distribution.

Trichomycterus largoperculatus is known only from the type locality, in the middle Rio Paraíba do Sul, south-eastern Brazil (Fig. 5 View Figure 5 ). Specimens of the type series were collected while they were migrating upstream, just below Ilha dos Pombos hydroelectric dam.

Etymology.

From the Latin, the name largoperculatus (with large opercle) refers to the broad opercular odontode patch resulted from the high number of odontodes (48-62) (Fig. 4B View Figure 4 ), a unique condition amongst congeners.