Trichomycterus mutabilicolor Costa, 2022

Costa, Wilson J. E. M., Mattos, José Leonardo O., Lopes, Sâmela, Amorim, Pedro F. & Katz, Axel M., 2022, Garypus sanasai Lin, Huang & Chang 2022, sp. nov., Zoological Studies 61 (11), pp. 1-13 : 4-10

Family Trichomycteridae Bleeker, 1858 Genus Trichomycterus Valenciennes, 1832

Trichomycterus mutabilicolor Costa , sp. nov. ( Figs. 2 , 3C, D , 4 ; Table 2) urn:lsid:zoobank.org:act:A02C0F12-B107-4662-AF6B-1AB26976BEE9

Holotype: UFRJ 12650, 82.6 mm SL; Brazil: São Paulo state: Cunha municipality: Cachoeira Mato Limpo, Riacho Pedacinho do Céu, a tributary of the Rio Taboão , which is a tributary of the Rio Manso , itself a tributary of the Rio Monjolo , upper Rio Paraitinga drainage, Rio Paraíba do Sul basin, 23°09'25"S 44°51'21"W, altitude about 1335 m asl; B. Mesquita and P.F. Amorim, 25 January 2020.

Paratypes: All from Brazil: São Paulo state: Cunha municipality: upper Rio Paraitinga drainage, Rio Paraíba do Sul basin. – UFRJ 12649, 37.3 mm SL; collected with holotype. – UFRJ 5697, 1, 47.9 mm SL; same locality as holotype; W. J. E. M. Costa, B. B. Costa and C. P. Bove, 8 March 2003. UFRJ 5652, 2, 36.0– 40.7 mm SL; UFRJ 5696, 1, 38.1 mm SL (C&S); same locality as holotype; W. J. E. M. Costa, B. B. Costa and C. P. Bove, 14 April 2001. – UFRJ 5698, 7, 26.8–43.8 mm SL; CICCAA 02712, 4, 27.8–35.2 mm SL; UFRJ 5699, 3 (C&S), 37.2–47.4 mm SL; Toca das Andorinhas, Rio Monjolo, Rio Paraitinga drainage, Rio Paraíba do Sul basin, 23°06'08"S 44°5l'56"W, altitude about 1200 m asl; W. J. E. M. Costa, B. B. Costa and C. P. Bove, 6 March 2003. – UFRJ 5700, 8, 33.2–45.7 mm SL; UFRJ 5625, 4, 34.1–56.6 mm SL (C&S); same locality and collectors as UFRJ 5698, 17 April 2001.

Diagnosis: Trichomycterus mutabilicolor is a member of the T. nigroauratus group, which is easily diagnosed by the presence of a folded laminar expansion of the lateral ethmoid border, just above the articular facet for the autopalatine ( Fig. 4A ; vs. absence). Trichomycterus mutabilicolor differs from all other species of the T. nigroauratus group by its flank colouration (brownish grey with a black stripe between snout and caudal fin base in specimens between about 26.8 and 56.6 SL length ( Fig. 3C ), and body yellowish grey with small dark brown spots in a specimen 82.6 mm SL mm SL (holotype, Fig. 3D ); vs. juveniles with a series of black elongate spots along body midline, sometimes coalesced to form a stripe, and adults with grey spots over pale brownish grey spots on flank in T. maculosus , always homogeneously black in T. quintus , and a persistent black stripe in large specimens of T. nigroauratus ), dorsal and anal fins fin more posteriorly placed relative to vertebrae counts (dorsal-fin origin at a vertical through the centrum of the 20th or 21nd vertebra, and the anal-fin origin at a vertical through the centrum of the 24th or 25th vertebra; vs. dorsal-fin origin at a vertical between the centrum of the 17th and the 19th vertebra, and the anal-fin origin at a vertical through the centrum of 22nd or 23rd vertebra), metapterygoid deeper than long ( Fig. 4B ; vs. longer than deep, Costa 2021: fig. 3D), a thicker opercle, with a short ventral process ( Fig. 4B ; vs. thinner, with relatively long ventral process, Costa 2021: fig. 3D); and a broad pelvic bone, its length excluding processes slightly longer than its width ( Fig. 4D ; vs. narrow, its length about three or four times its width, Costa 2021: fig. 6D).

Description: Morphometric data appear in table 1. Largest specimen examined 82.6 mm SL. Body moderately slender, subcylindrical and slightly depressed anteriorly, compressed posteriorly. Greatest body depth at vertical midway between pectoral and 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 anal-fin base end, straight on caudal peduncle. Anus and urogenital papilla at vertical through anterior third of dorsal-fin base. Head trapezoidal in dorsal view. Head surface with minute skin papillae. Anterior profile of snout slightly convex in dorsal view. Eye small, dorsally positioned in head. Posterior nostril located nearer anterior nostril than orbital rim. Tip of maxillary barbel reaching between anterior and middle portion of opercular patch of odontodes; tip of rictal barbel reaching anterior portion of interopercular patch of odontodes; tip of nasal barbel reaching between posterior margin of orbit and point midway between orbit and opercular patch of odontodes. Mouth subterminal. Jaw teeth pointed in specimens 50 mm SL or smaller, incisiform in holotype; teeth arranged in 3 or 4 irregular rows. Branchial membrane attached to isthmus only at its anterior point. Branchiostegal rays 7 or 8.

Dorsal and anal fins subtriangular; total dorsal-fin rays 11 or 12 (iii + II + 6–7), total anal-fin rays 10 (iii + II + 5). Anal-fin origin at vertical through posterior extremity of dorsal-fin base. Dorsal-fin origin at vertical through centrum of 20th or 21nd vertebra, anal-fin origin at vertical between centrum of 24th or 25th vertebra. Pectoral fin subtriangular in dorsal view, posterior margin slightly convex, first pectoral-fin ray terminating in filament reaching about 30% of pectoral-fin length without filament; total pectoral-fin rays 8 (I + 7). Pelvic fin truncate, its posterior extremity reaching urogenital papilla; pelvic-fin bases medially separated by small interspace; total pelvic-fin rays 5 (I + 4). Caudal fin truncate, posterior margin nearly straight, upper and lower corners rounded; total principal caudalfin rays 13 (I + 11 + I), total dorsal procurrent rays 16–19 (xv–xviii + I), total ventral procurrent rays 13–16 (xii–xv + I). Vertebrae 37–39. Ribs 13 or 14. 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: Supraorbital sensory canal continuous, connected to posterior section of infraorbital canal posteriorly. Supraorbital sensory canal with 3 pores: s1, adjacent to medial margin of anterior nostril; s3, adjacent and just posterior to medial margin of posterior nostril; and s6, at transverse line through posterior half of orbit; s6 nearer to its lateral homologous pore than to orbit. Infraorbital 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 ): Anterior margin of mesethmoid gently concave, mesethmoid subcylindrical. Antorbital thin, approximately elliptical in dorsal view. Sesamoid supraorbital elongate, rod-like, without lateral processes, its length about two times and half antorbital length. Premaxilla long, subrectangular, narrowing laterally. Maxilla boomerang-shaped, slender, about equal to premaxilla in length or slightly longer, almost straight, posterior process rudimentary. Autopalatine subrectangular in dorsal view when excluding posterolateral process, broad, its shortest width about half autopalatine length, lateral margin nearly straight, medial margin slightly concave; latero-posterior process of autopalatine triangular, short, its length about two thirds autopalatine length. Dorsal surface of autopalatine about plain, without distinctive ridges. Autopalatine articular facet for lateral ethmoid shell-shaped dorsally, without processes, articular facet for vomer minute. Distinctive flap close mesethmoid articular facet for autopalatine. Anterodorsal extremity of lateral ethmoid with slight lateral expansion. Lateral margin of lateral ethmoid continuous, without processes.

Suspensorium and opercular apparatus ( Fig. 4B ): Metapterygoid subtriangular, deeper than long, anterior margin curved, posterior portion terminating in slender extension. Quadrate robust, dorsoposterior outgrowth in close proximity to hyomandibula anterior outgrowth. Hyomandibula long, with well-developed anterior outgrowth; middle portion of dorsal margin of hyomandibula outgrowth. Opercle moderately robust, depth of opercular patch of odontodes about three quarters of length of dorsal articular cartilage of hyomandibula; dorsal process of opercle short and blunt, about half opercle length; ventral process supporting ligamentous connections to interopercle short; well-developed flaps adjacent to articular facets for hyomandibula and preopercle. Opercular odontodes 16–20; odontodes pointed, straight to slightly curved, arranged in irregular transverse rows. Interopercle long, about four fifths of hyomandibula length; dorsal interopercular process constricted at its base, anteriorly expanded on its dorsal tip. Interopercular odontodes 35–44; odontodes pointed, about straight, arranged in irregular longitudinal rows. Preopercle compact, with short ventral projection.

Branchial arches ( Fig. 4C ): Basibranchials 2 and 3 subcylindrical, basibranchial 2 slightly shorter and wider than basibranchial 3; basibranchial 4 cartilage sub-triangular, wider than long. Hypobranchial 1 subcylindrical, abruptly widening at its lateral tip; hypobranchial 2 subtriangular, osseous portion longer than cartilaginous portion; hypobranchial 3 subtrapezoidal, osseous portion small and narrow, cartilaginous portion broad. Ceratobranchial 1 broad in its proximal tip, gradually narrowing to its distal tip; ceratobranchials 2 and 3 widened in their middle portion, with shallow concavity on posterior margin of basal portion; ceratobranchial 4 sub-rectangular; ceratobranchial 4 accessory cartilage minute; ceratobranchial 5 boomerang-shaped, its largest width nearly equal to width of ceratobranchial 4; 23–25 small, slightly curved teeth on ceratobranchial 5 tooth patch. Epibranchial 1 slender, with well-developed sharp anterior uncinate process; epibranchial 2 slender, with rudimentary anterior uncinate process; epibranchial 3 slender, with well developed, curved posterior uncinate process; epibranchial 4 broad, sub-rectangular, proximal portion broader than distal portion. Pharyngobranchial 3 short, subcylindrical; pharyngobranchial 4 longer, slightly curved; 20– 22 small, curved teeth on pharyngobranchial 4 dentigerous plate.

Pelvic girdle ( Fig. 4D ): Pelvic bone broad, its length excluding processes slightly longer than its width; external and internal anterior processes similar in length, longer than pelvic bone excluding processes; antero-medial process well-developed, about one quarter to one third internal anterior process length; posterior process well-developed, about straight, posteriorly directed.

Colouration in life ( Fig. 3C–D ): In juvenile specimens, between about 25 and 40 mm SL ( Fig. 3C ), trunk and head light brownish grey, with midlateral black stripe between post-orbital area and caudal peduncle end; ventral surface of trunk and head light grey. Opercular and interopercular patches of odontodes light grey. Nasal barbel brown, maxillary and rictal barbels grey. Iris dark brown, with narrow pale-yellow line around pupil. Fins hyaline, with melanophores concentrated on mid-basal portion of caudal fin. Specimens between about 45 and 55 mm SL, similar to juvenile specimens, but stripe lighter, and with faint brown spots above flank stripe and minute brown dots below. In large specimen, 82.6 mm SL (holotype, Fig. 3D ), trunk and head pale brownish yellow, with small dark brown spots, more concentrated on head, anterior portion of flank and mid-posterior portion of caudal peduncle; ventral surface of trunk and head light yellowish grey. Opercular and interopercular patches of odontodes light grey. Nasal barbel brown, maxillary and rictal barbels yellowish grey. Iris dark brown, with narrow pale-yellow line around pupil. Fins yellowish hyaline, with great concentration of dark brown spots on basal portion.

Colouration in alcohol: Similar to life colouration, but with pale colours.

Etymology: From the Latin mutabilicolor (changing colour), referring to the striking ontogenetic colouration change.

Distribution and habitat notes: Trichomycterus mutabilicolor is known from two sites in the upper section of the Rio Paraitinga drainage, Rio Paraíba do Sul basin, in altitudes between 1200 and 1335 m asl ( Fig. 5 ). The water was clear and river bottom comprised rocks, gravel and sand ( Fig. 3A–B ). Specimens of the type series were collected within leaf litter just bellow waterfalls, about 40–80 cm depth.

Figures

Fig. 2. Trichomycterus mutabilicolor Costa sp. nov., UFRJ 12650, holotype, 82.6 mm SL. (a), left lateral view; (b), dorsal view; (c), ventral view.

Fig. 3. Habitat and live colouration of Trichomycterus mutabilicolor Costa sp. nov. (a), Cachoeira Mato Limpo, Riacho Pedacinho do Céu, upper Rio Paraitinga drainage, the type locality (23°09'25"S 44°5l'21"W); (b) Toca das Andorinhas, Rio Monjolo, upper Rio Paraitinga drainage (23°06'08"S 44°5l'56"W); (c) UFRJ 12649, 37.3 mm SL, paratype, DNA sequence used in the molecular analysis; (d) UFRJ 12650, 82.6 mm SL, holotype, DNA sequence used in the molecular analysis.

Fig. 4. Osteological structures of Trichomycterus mutabilicolor Costa sp. nov. (a), mesethmoidal region and adjacent structures, middle and left portion, dorsal view; (b), left jaw suspensorium and opercular apparatus, lateral view; (c), middle and left portion of brachial arches, ventral view of dorsal elements on left, dorsal view of ventral elements on right; (d), left pelvic bone, ventral view. Abbreviations: ac4, accessory cartilage basibranchial 4; b2–3, basibranchials 2–3; bc4, cartilaginous basibranchial 4; c1–5, ceratobranchials 1–5; e1–4, epibranchials 1–4; h1–3, hypobranchials 1–3; p3, pharyngobranchial 3; lef, lateral ethmoid flap; pt4, pharyngobranchial 4 tooth-plate. Larger stippling represents cartilages.

Fig. 5. Geographical distribution of the Trichomycterus nigroauratus group. Dot, T. maculosus; lozenges, T. nigroauratus; pentagons, T. quintus; stars, T. mutabilicolor Costa sp. nov. Red symbols indicate type localities. Arrows indicate the direction of the main river flow.