Trichomycterus tropeiro, Ferrer, Juliano & Malabarba, Luiz R., 2011

Ferrer, Juliano & Malabarba, Luiz R., 2011, A new Trichomycterus lacking pelvic fins and pelvic girdle with a very restricted range in Southern Brazil (Siluriformes: Trichomycteridae), Zootaxa 2912, pp. 59-67 : 60-64

Trichomycterus tropeiro , new species

( Figs. 1–2 , Table 1 )

Holotype. MCP 46171, 82.3 mm SL; Brazil: State of Rio Grande do Sul, Municipality of São José dos Ausentes; rio das Antas, 28º47'01"S 49º58'56"W, D. Gelain, J. Bastos, T. Dias, T. Hasper, 16 Jan 2001.

Paratypes. MCP 10624, 1, 87.4 mm SL, Brazil, State of Rio Grande do Sul, Municipality of Cambará do Sul, locality of Ouro Verde, rio das Antas, 28º51'00"S 50º01'25"W, C.A. Lucena, L. R. Malabarba, R. Reis, 1 May 1985. UFRGS 4845, 2, 39.5–39.7 mm SL, Brazil, State of Rio Grande do Sul, Municipality of São José dos Ausentes, stream tributary of the rio das Antas, 28º48'36''S 49º59'36"W, L. R. Malabarba, A. Cardoso, A. Schwarzbold, L. Sazinski, 6 Jan 2000. All the following lots from Brazil, State of Rio Grande do Sul, Municipality of São José dos Ausentes, rio das Antas: MCP 46172, 1, 81.6 mm SL, collected with holotype. MCP 46173, 1, 58.3 mm SL, 28º47'07"S 49º58'55"W, A. Cardoso, D. Gelain, J. Bastos, T. Hasper, 21 Apr 2001, LIRP 8154, 1, 96.1 mm SL, 28º47'01"S 49º58'56"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 25 Aug 2000. LIRP 8155, 1, 71,7 mm SL, 28º47'01"S 49º58'56"W, D. Gelain, J. Bastos, J. Anza, T. Dias, T. Hasper, 30 Jul 2001. MNRJ 38508, 1, 77.7 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 29 Oct 2000. MNRJ 38509, 1, 74.6 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 20 Dec 2000. UFRGS 8816, 1, 77.7 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 20 Dec 2000. MZUSP 108296, 1, 55.5 mm SL, 28º47'11"S 49º59'04"W, A. Cardoso, A. Schwarzbold, L. R. Malabarba, L. Sazinski, 6 Jan 2000. MZUSP 108297, 1, 83.3 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, L. R. Malabarba, T. Dias, 17 Mar 2001. MZUSP 108298, 1, 34.5 mm SL, 28º47'07"S 49º58'55"W, A. Cardoso, D. Gelain, J. Bastos, T. Hasper, 21 Apr 2001. UFRGS 5563, 1, 91.7 mm SL, 28º47'07"S 49º58'55"W, A. Cardoso, D. Gelain, J. Bastos, T. Hasper, 21 May 2001. UFRGS 8813, 2 (c&s), 73.4–84.0 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 22 Jun 2001. UFRGS 8815, 1 (c&s), 62.8 mm SL, 28º47'01"S 49º58'56"W, D. Gelain, J. Anza, J. Bastos, T. Hasper, 20 Dec 2000. UFRGS 8818, 2, (1 c&s), 46.8–85.1 mm SL, 28º47'01"S 49º58'56"W, D. Gelain, J. Anza, J. Bastos, T. Dias, T. Hasper, 19 May 2001. UFRGS 8819, 1, 28.0 mm SL, 28º47'07"S 49º58'55"W, D. Gelain, J. Anza, J. Bastos, L. R. Malabarba, T. Dias, 17 Mar 2001.

Diagnosis. Trichomycterus tropeiro is distinguishable from other species of the genus by the absence of the pelvic girdle, except T. candidus and T. catamarcensis . Trichomycterus tropeiro differs from T. candidus by head length (20.4–23.1 vs. 14.7–16.1% SL); pectoral-fin length (12.8–14.7 vs. 8.6–9.3% SL); interorbital distance (19.6–25.3 vs. 26.6–32.3% HL); number of dorsal procurrent caudal-fin rays (13–14 vs. 16–19); ventral procurrent caudal-fin rays (9–10 vs. 16–18); pectoral-fin unbranched rays (6 vs. 5); and branchiostegal rays (9 vs. 8). Trichomycterus tropeiro differs from T. catamarcensis by body depth (13.9–18.1 vs. 8.9–12.7% SL); caudal peduncle depth (10.9–13.5 vs. 7.1–8.5% SL); head length (20.4–23.1 vs. 15.6–19.4% SL); interorbital distance (19.6–25.3 vs. 26.3–34.7% HL); number of dorsal-fin unbranched rays (7 vs. 8–9); pectoral-fin unbranched rays (6 vs. 7); analfin unbranched rays (5 vs. 7–9); ventral procurrent caudal-fin rays (9–10 vs. 11–12); branchiostegal rays (9 vs. 5– 6); and pleural ribs (13–14 vs. 18–20).

Description. Morphometric data for holotype and paratypes given in Table 1 . Body elongate, roughly cylindrical close to head and gradually more compressed in trunk towards caudal-fin. Dorsal e ventral profiles of head straight. Profiles of trunk straight dorsally and slightly convex ventrally. Dorsal and ventral profiles of caudal peduncle straight. Integument thick, especially over base of dorsal-fin and anal-fin. Small papillae covering entire surface of skin, most prominent on lips and ventral, dorsal, and lateral surfaces of head.

Holotype Range Mean SD Head wide and depressed, longer than wide, the transversal section at posterior tip of opercle wider than anteriorly at nostril, snout slightly rounded. Lateral region of eye slightly swollen by jaw muscles in both large and small specimens. Eyes rounded, well defined rim, dorsally oriented, covered by thin and transparent skin, not distinctly separated from surface of eyeball. Ocular structures readily visible on surface of skin, not deeply sunken. Orbital rim not free. Anterior nostril larger than posterior nostril, surrounded by fleshy flap of integument, posterolaterally continuous with nasal barbel. Posterior nostril surrounded anteriorly by thin flap of integument. Gill openings not constricted, united to isthmus anteriorly. Five or six branchiostegal rays externally visible from below (9 in c&s), covered with thick skin. Mouth subterminal, its corners laterally or slightly posteriorly oriented. Lower lip with conspicuous fleshy lobes along lateral limits and internal to origin of rictal barbels. Lower lip covered with small papillae. Anterior margin of upper lip rounded. Small papillae on external surface of upper lip and large papillae continuous inside mouth at region of teeth attachment. Upper lip continuous with dorsal surface of head.

Barbels with large bases and tapering gradually toward to the tip. Nasal barbels thick always surpassing posterior margin of eye but not reaching opercular patch of odontodes. Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril. Maxillary barbels reaching or surpassing posterior tip of interopercular patch of odontodes. Rictal barbels shorter than maxillary barbels reaching the interopercular patch of odontodes.

Opercular path of odontodes rounded with 12–14 odontodes. Interopercular path of odontodes elongate with 18–24 odontodes. Odontodes on both opercle and interopercle gradually increasing in size and curving medially posteriorly. Odontodes covered by thick integument.

Supraorbital sensory canal complete and infraorbital sensory canal incomplete. Infraorbital anterior section pores i1 and i3, and posterior section pores i10 and i11. Supraorbital pores s1, s3 and s6. Two pores s6 paired at interorbital space. Postotic pores po1 and po2 ( Fig. 2 ). Lateral-line canal very short, with 2 pores (four in two paratypes).

Pectoral-fin with distal margin rounded, I,6 rays, first ray not prolonged as filament. Dorsal-fin with distal margin rounded, semicircular when fin expanded, iii,II,7 rays. Anal-fin slightly smaller than dorsal-fin, with distal margin rounded, ii,II,5 rays, origin at vertical through middle portion dorsal-fin. Pelvic-fin and pelvic girdle absent. Caudal-fin with distal margin straight and the dorsal e ventral edges rounded, II,5–6,II principal rays, branched rays splitting tree times. Procurrent caudal-fin rays 13 or 14 dorsally and 9 or 10 ventrally.

Free vertebrae 37 or 38. Ribs 13 or 14 pairs; first thickest; 10th, 11th, 12th longest; last rib rudimentary. Dorsal-fin pterygiophores 8, first one inserting anterior to 19th or 20th neural spine. Anal-fin pterygiophores 6, first one inserting anterior to 22th or 23th hemal spine.

Coloration in alcohol. Flank and dorsum of body with irregular dark spots variable in size and shape, on lighter background, larger and more concentrated on dorsum of trunk; gradually becoming more scattered and smaller on sides and posterior third of trunk; completely absent in the ventral surface of trunk. Dorsal surface of head with irregular dark blotches variable in size and shape, larger and more concentrated in medial posterior region; gradually becoming more scattered and smaller on lateral and anterior region; completely absent on ventral surface. Opercular and interopercular path of odontodes pigmentation continuous with that on remainder of head. Upper lip with small spots similar to those on rest of head. Lower lip with small dark fields close to its anterior margin. Pectoral-fin with small spots along basal portion, remainder fin without spots and becoming lighter toward to tip. Dorsal-fin with small spots along anterior edge and basal portion, remainder fin without spots becoming lighter toward to tip. Anal-fin with dark pigmentation in basal portion becoming lighter toward to tip, pigmentation generally fainter than other fins. Caudal-fin with small spots along basal portion, remainder fin without spots becoming lighter toward to tip. Nasal and maxillary barbels with dark pigmentation along entire length, on both surfaces ( Fig. 1 ).

Etymology. The name is an allusion to the old drovers paths that connected the States of Rio Grande do Sul and São Paulo and crossed the Municipalities of São José dos Ausentes and Cambará do Sul. A name in apposition.

Distribution. Known from the localities of the type series, three points located in the rio das Antas, two of them very close, and in one tributary stream ( Fig. 3 ). The rio das Antas is part of laguna dos Patos system, having a length of 390 km to its confluence with the rio Guaporé, where both form the rio Taquari, crossing over 140 km before emptying into the rio Jacuí.

Ecological notes. Trichomycterus tropeiro occurs in environments with clear water, fast current, bottom composed of gravel, pebbles and stones, above 1000 m. The stomach of the two specimens cleared and stained contained nymphs of Ephemeroptera and larvae of Diptera (Chironomidae) and Trichoptera. The following species of fish occur syntopically with T. tropeiro : Astyanax brachypterygium Bertaco & Malabarba, 2001 ; Astyanax sp., Cnesterodon brevirostratus Rosa & Costa, 1993 ; Eurycheilichthys sp., Jenynsia eirmostigma Ghedotti & Weitzman, 1995 and Pareiorhaphis hystrix ( Pereira & Reis, 2002) .

Trichomycterus tropeiro seems to be relatively rare, with low populational densities. Almost all specimens were collected near the same locality, during an one year ecological study with monthly collecting samples. Even with that frequency all the collecting effort resulted in 22 specimens only, with a maximum of two, usually one specimen collected monthly in each locality.

Figures

FIGURE 1. Trichomycterus tropeiro, MCP 46171, holotype, 82.3 mm SL, from the rio das Antas, Municipality of São José dos Ausentes, State of Rio Grande do Sul, Brazil.

FIGURE 2. Head of Trichomycterus tropeiro, MZUSP 108296, paratype, 55.5 mm SL. Dorsal view. Abbreviations: s 1, s 3 and s 6, pores of the supraorbital sensory canal; i 1 and i 3, pores of anterior section of the infraorbital sensory canal; i 10 and i 11, pores of posterior section of the infraorbital sensory canal; po 1 and po 2, pores of the postotic sensory canal. Scale bar = 2 mm.

FIGURE 3. Geographic distribution of Trichomycterus tropeiro (red circle) and localities sampled around the type locality registered in the fish collections at MCP, MNRJ, MZUSP, and UFRGS (black dots). Modified from Malabarba et al. (2009). Each symbol may represent more than one lot.

Tables

TABLE 1. Morphometric data for holotype and paratypes (except UFRGS 8815) of Trichomycterus tropeiro (n = 21 including the holotype). SD = Standard deviation.

Standard length (mm) Percents of Standard Length Head length	82.3 20.4	28.0-96.1 68.8 20.4-23.1 21.7	– 0.6
Predorsal length Preanal length Scapular girdle width Pectoral–fin length	64.9 70.2 14.5 12.8	62.9-66.4 64.6 67.7-72.7 70.9 14.0-15.9 15.0 12.8-14.7 13.6	0.8 1.2 0.5 0.5
Caudal peduncle length Caudal peduncle depth	20.8 11.7	19.4-23.4 20.8 10.9-13.5 12.0	1.0 0.8
Body depth Length of dorsal–fin base Length of anal–fin base Percents of Head Length Head width Nasal barbel length	15.2 10.0 9.1 83.9 66.0	13.9-18.1 15.2 10.0-12.7 11.5 8.1-10.2 9.1 77.8-87.2 82.9 49.7-66.1 58.2	1.1 0.6 0.5 2.6 4.4
Maxillary barbel length Rictal barbel length Snout length Interorbital	59.0 57.9 48.0 25.3	59.0-70.3 65.5 47.6-60.9 54.9 42.2-50.1 45.8 19.6-25.3 22.1	3.1 3.9 2.1 1.4
Mouth width Eye diameter	46.2 6.9	41.3-54.0 48.5 6.7-12.1 8.5	3.3 1.5
Supra–orbital pore distance	7.3	5.3-10.0 8.1	1.2