Trichomycterus immaculatus ( Eigenmann and Eigenmann, 1889 )

Costa, Wilson J. E. M., Katz, Axel M., Mattos, José Leonardo O., Amorim, Pedro F., Mesquita, Beatrizz O., Vilardo, Paulo J. & Barbosa, Maria Anais, 2020, Historical review and redescription of three poorly known species of the catfish genus Trichomycterus from south-eastern Brazil (Siluriformes: Trichomycteridae), Journal of Natural History 53 (47 - 48), pp. 2905-2928 : 2916-2919

Trichomycterus immaculatus ( Eigenmann and Eigenmann, 1889)

( Figures 1b , 2d–f )

Pygidium immaculatum Eigenmann and Eigenmann, 1889: 52 (syntypes: MCZ 8300 , 128– 171 mm SL (photographs available at http://acsi.acnatsci.org/base/image_list.html? search=true&orderby=genus&genus= Pygidium &trivial=immaculatum; type locality: Juiz de Fora [Minas Gerais state, Brazil], Rio Parahybuna [Rio Paraibuna, Rio Paraíba do Sul basin]).

Pygidium paquequerense P. Miranda Ribeiro 1943: 2 (holotype: MNRJ 1159 , 44 mm in total length; type locality: Rio Paquequer Grande, Estado do Rio de Janeiro).

Material examined

All from Brazil, Rio Paraíba do Sul basin . Estado de Minas Gerais: Município de Juiz de Fora (Rio Paraibuna drainage): – MCZ 8300 , syntype (photographs, radiographs); Rio Paraibuna at Juiz de Fora; H .W. Halfeld, 1854. – UFRJ 3593, 1; Córrego da Invernada, tributary of Rio do Peixe ; F .A. Bockmann and P.M.C. Araújo, 3 May 1996. – UFRJ 7265, 1 (C&S); Município de Lima Duarte: road between Lima Duarte and Ibitipoca , Rio do Peixe drainage; M .A. Barbosa et al., 21 April 2006. – UFRJ 10,001, 1; same locality as UFRJ 7265; A .M. Katz and F. Ottoni, 2 May 2014. Município de Bocaina de Minas (Rio Paraibuna drainage, Rio Preto subdrainage): UFRJ 12051, 1 (C&S), Rio Preto at Ponte dos Cachorros, - 22.30666S, - 44.50805W, about 1000 m asl; B . Mesquita et al., 28 September 2018. – UFRJ 12050, 1; Ribeirão das Flores, - 22.26944S, - 44.50583W, about 1000 m asl; W.J.E.M. Costa et al., 26 September 2018. Rio de Janeiro State: Município de Resende (Rio Paraibuna drainage, Rio Preto subdrainage): – UFRJ 609, 3; Rio Marimbondo , - 22.33416S, - 44.54361W, 1035 m asl; W .J.E.M. Costa and C.P. Bove, 9 November 1991. – UFRJ 706, 3; Rio Marimbondo , - 22.33416S, - 44.54361W, 1035 m asl; W .J.E.M. Costa and U. Neira, 1 December 1991. – UFRJ 10489, 1 (C&S); same locality as UFRJ 609; W .J.E.M. Costa et al., 4 June 2015. – UFRJ 10680, 1; same locality as UFRJ 609; W .J.E.M. Costa et al., 17 July 2015. – UFRJ 11969, 1 (DNA); same locality as UFRJ 609; W .J.E.M. Costa et al., 25 September 2018. Município de Teresópolis (Rio Piabanha drainage, Rio Paquequer subdrainage): MNRJ 1159 , holotype of P . paquequerense; Rio Paquequer Grande ; A .L. Carvalho. UFRJ 7595, 1 (DNA); Rio Canoas ; F .P. Ottoni, 31 December 2007. – UFRJ 7272, 2 (1 C&S); Rio Canoas ; F .P. Ottoni et al., 30 September 2006. Município de Resende: UFRJ 12602, 1; Rio Alambari , - 22.41333S, - 44.50388W, about 515 m asl; B . Mesquita and P. Amorim, 31 October 2018.

Diagnosis

Trichomycterus immaculatus is distinguished from all other congeners, except T. caipora , T. giganteus , T. nigricans , T. pradensis and T. santaeritae , by having 9 pectoral-fin rays (vs 6–8). Trichomycterus nigricans differs from all other species here osteologically examined, except T. caipora , T. immaculatus and T. santaeritae , by the presence of a pronounced posterior process on the maxilla ( Figure 2d ) (vs rudimentary process). Also distinguished from all congeners except T. caipora , T. nigricans and T. santaeritae by having the caudal fin emarginate at least in larger specimens (vs truncate or subtruncate, rarely bilobed). Trichomycterus immaculatus differs from T. caipora , T. nigricans and T. santaeritae by having a short maxilla, distinctively shorter than the premaxilla ( Figure 2d ) (vs about as long as premaxilla or longer); a compact autopalatine, its width about half autopalatine length without posterolateral process (vs slender, about two-fifths autopalatine length); a slender opercular odontode patch, its depth about two-fifths of the opercle length, with about 15–20 odontodes ( Figure 2e ) (vs robust, its depth about three-quarters of the opercle length, with about 25 odontodes); and the anterior extremity of hypobranchial 3 unbranched ( Figure 2f ) (vs branched).

Description

Morphometric data are given in Table 1. Largest specimen examined 117.0 mm SL. Body moderately slender, subcylindrical and slightly depressed anteriorly, compressed posteriorly. Greatest body depth at vertical just in front 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. Skin papillae minute. Anus and urogenital papilla in vertical through middle of dorsal-fin base, nearer tip of pelvic fin than anal-fin origin. Head trapezoidal in dorsal view. Anterior profile of snout convex in dorsal view. Eye small, dorsally positioned in head. Posterior nostril located approximately midway between anterior nostril and anterior orbital rim. Maxillary and rictal barbels similar in size, reaching between middle and posterior edge of interopercular patch of odontodes; tip of nasal barbel reaching between anterior margin of orbit and point just posterior to orbit. Mouth subterminal. Jaw teeth pointed, arranged in 4 or 5 irregular rows; premaxillary teeth nearly straight, dentary teeth slightly curved inside mouth. Branchial membrane attached to isthmus only at its anterior point. Branchiostegal rays 7.

Dorsal and anal fins subtriangular; total dorsal-fin rays 12 or 13 (iii + I–II + 8), total analfin rays 9–10 (ii–iii + II + 5); anal-fin origin in vertical through posterior portion of dorsal-fin base. Dorsal-fin origin in vertical through centrum of 18th vertebrae; anal-fin origin in vertical between centra of 22nd or 23rd vertebrae. Pectoral fin subtriangular in dorsal view, first pectoral-fin ray terminating in short filament reaching about 10% 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 minute interspace; total pelvic-fin rays 5 (I + 4). Caudal fin truncate to slightly emarginated in specimens above 80 mm SL, posterior margin straight to slightly concave; total principal caudal-fin rays 13 (I + 11 + I), total dorsal procurrent rays 16–19 (xv–xviii + I), total ventral procurrent rays 13–15 (xii–xiv + I). Vertebrae 36. Ribs 12 or 13.

Laterosensory system. Supraorbital sensory canal continuous, connected to infraorbital sensory canals posteriorly. Supraorbital sensory canal with 3 pores: s1, adjacent to medial margin of anterior nostril; s3, adjacent to medial margin of posterior nostril; and s6, on middle part of dorsal surface of head, in transverse line just posterior to orbit; pores s6 medially in close proximity. Infraorbital sensory canal arranged in 2 segments, each with 2 pores; anterior segment with pore i1, in transverse line through anterior nostril, and pore i3, in 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, in vertical line above posterior portion of interopercular patch of odontodes, and po2, in vertical line above posterior portion of opercular patch of odontodes. Lateral line of body short, with 2 pores, posterior-most pore in vertical just posterior to pectoralfin base.

Mesethmoidal region and adjacent structures ( Figure 2d ). Anterior margin of mesethmoid approximately straight, mesethmoid cornu robust, subcylindrical, tip rounded. Antorbital and sesamoid supraorbital narrow, rod-like, sesamoid supraorbital long, its length about 2.5 times antorbital length. Premaxilla sub-retangular in dorsal view, without processes. Maxilla boomerang-shaped, slender, shorter than premaxilla, slightly curved, with prominent posterior process. Autopalatine subrectangular in dorsal view when excluding posterolateral process, moderate in width, its shortest width about half autopalatine length without posterolateral process, lateral and medial margins slightly concave; no concavity on posterior margin of autopalatine between posteromedial corner and posterior articulatory process; latero-posterior process of autopalatine triangular, its length about half autopalatine length. Posterior articulatory process well developed, shell-shaped.

Suspensorium and opercular apparatus ( Figure 2e ). Metapterygoid subtriangular, longer than deep, anterior face curved, posterior and ventral face nearly straight, posterior margin separated by anterior hyomandibular flap by small interspace. Quadrate robust, dorsoposterior flap continuous to hyomandibular flap. Hyomandibula broad, with welldeveloped flap; middle portion of dorsal margin of hyomandibular flap with shallow concavity; postero-dorsal process of hyomandibula moderate, rounded to slightly pointed. Opercle slender, its smallest depth about one-third opercle length; dorsal process of opercle short and blunt, about one-third opercle length; ventral process of opercle moderate, about equal to opercle length; odontode patch relatively slender, its depth about two-fifths opercle length, with about 15–20 odontodes; odontodes pointed, arranged in irregular transverse rows. Interopercle long, about two-thirds hyomandibula length; dorsal interopercular process with shallow anterior concavity; interopercular odontode patch relatively slender, its length about 3 times depth of opercular odontodes patch, with 55–60 odontodes; odontodes pointed, arranged in irregular longitudinal rows. Preopercle compact, with pronounced ventral flap.

Branchial arches ( Figure 2f ). Basibranchials 2 and 3 subcylindrical, slightly constricted in their medial portion, basibranchial 2 slightly longer and wider; basibranchial 4 cartilage elliptical, longer than wide. Hypobranchial 1 subcylindrical; hypobranchials 2 and 3 subtriangular, anterior extremities unbranched. Ceratobranchial 1 broad in its proximal tip, 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 subrectangular; ceratobranchial 5 sub-rectangular, postero-proximal portion bearing patch of small, slightly curved, conical teeth. Epibranchial 1 slender, with well-developed sharp 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-retangular, proximal portion broader than distal portion; epibranchial 5 cartilage (= accessory element of ceratobranchial 4) minute. Pharyngobranchial 3 short, subcylindrical; pharyngobranchial 4 long, bearing broad dentigerous tooth-plate with curved conical teeth.

Colouration in life ( Figure 1b ). Just after collection, all body black, except ventral portion of head and trunk grey, distal portion of fins hyaline, maxillary and rictal barbels grey, and opercular and interopercular patches of odontodes light grey; after collection, black colouration becoming dark brown. Iris dark brown, with narrow pale yellow line around pupil. No colouration polymorphism recorded.

Colouration in alcohol. Dorsal and lateral surface of head and trunk homogeneously dark grey to brown. Venter pale grey. Nasal barbels pale brown, with dark brown edges. Maxillary and rictal barbels pale grey. Fins dark brown on basal portion, with great concentration of melanophores on caudal-fin base, fin extremities pale grey.

Distribution and habitat

Trichomycterus immaculatus is geographically widespread in the Rio Paraíba do Sul basin ( Figure 3 ) (see discussion below). All specimens were collected hidden under large rocks, suggesting nocturnal habits.

Figures

Figure 1. Live specimens, left lateral view, of: a, Trichomycterus nigricans, UFRJ 10,996, 69.7 mm SL; b, Trichomycterus immaculatus, UFRJ 12,050, 62.9 mm SL; c, Trichomycterus santaeritae, UFRJ 12,592, 56.8 mm SL. All were photographed a few hours after collection.

Figure 2. Osteological features of Trichomycterus nigricans (a–c), T. immaculatus (d–f), and T. santaeritae (g–i): A, D, G, mesethmoidal region and adjacent structures, middle and left portion, dorsal view; B, E, H, left suspensorium and opercular apparatus, lateral view; C, F, I, middle and left portion of brachial arches, ventral view of dorsal elements on left, dorsal view of ventral elements on right. Larger stippling represents cartilage. Abbreviations: aip, anterior interopercular projection; b2–3, basibranchials 2–3; bc4, cartilaginous basibranchial 4; c1–5, ceratobranchials 1–5; e1–4, epibranchials 1–4; ec5, epibranchial 5 cartilage (= accessory element of ceratobranchial 4); h1–3, hypobranchials 1– 3; hdb, hypobranchial anterior branching; pmp, posterior maxillary process; p3, pharyngobranchial 3; pt4, pharyngobranchial 4 tooth-plate.

Figure 3. Geographical distribution of the Trichomycterus nigricans species group: diamonds, T. santaeritae; square, T. caipora; stars, T. immaculatus; triangles, T. nigricans.