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Trichomycterus trefauti ZBK new species

(Fig. 2, Table 1)

Holotype : MZUSP 79911, 49.5 mm SL, riacho Andrequicé , tributary of rio Paraúna , itself a tributary of rio das Velhas (rio São Francisco basin), approximately 18°30’S , 43°30’W , Município de Trinta Réis , Minas Gerais , Brazil ; collected by M.T.U. Rodrigues; 8 September1986 .

Paratypes : Collected with the holotype : MZUSP 36966, 5 ex. (36.6-54.2 mm SL; 3 C&S) ; MPEG 7896, 2 ex. (37.2-47.3mm SL) .

Diagnosis: Trichomycterus trefauti ZBK differs from all other known members of the subfamily Trichomycterinae by the autapomorphic presence of an elliptical, vertically elongated, brown spot, at caudal-fin base (vs. without elliptical spot at caudal-fin base), and the combination of homogeneously gray color pattern (vs. yellowish, presence of stripes or bands, or lack of color pattern), first pectoral-fin ray prolonged as a filament (vs. not prolonged), subterminal mouth (vs. inferior or terminal mouth), two supraorbital pores at interorbital space (vs. one supraorbital pore at mesial line), caudal fin truncate with attenuated edges (vs. caudal fin rounded), pelvic fins covering anus and urogenital openings (vs. not covering), interorbital space very wide - 39.8-45.9 % HL (vs. more or less than 39.8- 45.9 % HL), maxillary barbels very long - 84.2-93.0 % HL (vs. more or less than 84.2- 93.0 % HL), rictal barbels very long - 67.6-74.3 % HL (vs. more or less than 67.6-74.3 % HL).

Description: Morphometric data for holotype and paratypes are given in Table 1.

Body elongate, roughly cylindrical close to head and gradually more compressed towards caudal fin. Dorsal and ventral profiles of trunk slightly convex. Dorsal and ventral profiles of caudal peduncle straight (Fig. 2). Integument thick, especially over base of pectoral and caudal fins. Small papillae on lips, and scattered on dorsal surface of head.

Head wide and depressed, trapezoidal, slightly longer than wide, transverse section at posterior tip of opercle wider than anteriorly at nostril, anterior margin slightly rounded. Head lateral to eye slightly swollen by jaw muscles in large and small specimens. Dorsal and ventral profiles of head convex. Eyes rounded, dorsolaterally oriented. Eye covered by thin skin, transparent at its center, gradually opaque towards rim, distinctly separated from surface of eyeball. Ocular structures readily visible on surface of skin, not deeply sunken. Orbital rim not free. Anterior nare slightly larger than posterior, surrounded by fleshy flap of integument. Posterior nare surrounded anteriorly by thin flap of integument. Anterior and posterior nares about one third of eye diameter. Gill membranes thick, united to isthmus only at anteriormost point, forming small free fold across the isthmus. Gill openings not constricted. Branchiostegal rays 6-8 (6 in Holotype ) visible from below (7-8 in C&S). Mouth subterminal, its corners laterally oriented. Lower lip with conspicuous lateral fleshy lobes, internal to origin of rictal barbels. Anterior margin of upper lip slightly rounded. Small papillae on external surface of upper lip and large papillae inside mouth at region of teeth attachment. Barbels long (nasal 74.3-69.8; maxillary 93.0-84.2; and rictal barbel length 74.3-67.6 % of head length). Barbels with broad bases, gradually narrowing towards tip. Nasal barbels reaching median odontodes of interopercle; maxillary barbels reaching base of pectoral fin; rictal barbels reaching last interopercular odontode. Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril. Interopercular patch of odontodes rounded, with 34-36 conical odontodes. Opercular patch of odontodes rounded, with 14-16 conical odontodes. Supraorbital canal complete and infraorbital incomplete. Infraorbital anterior section pores i1 and i3 , and posterior section pores i10 and i11. Supraorbital pores s1, s2 and s4. Two pores s4 at interorbital space.

Pectoral-fin margin truncate, I/6 rays, first ray longest with filamentous extension. Dorsal fin with margin semicircular when expanded, II/7 rays, third and fourth rays longest. Anal fin slightly elongate in overall shape, smaller than dorsal fin, I/6 rays, third ray longest, origin at vertical through sixth dorsal-fin ray. Pelvic fins with origin anterior to dorsal-fin origin, rounded margin beyond urogenital and anal openings when extended, 5 rays, second and third rays longest. Caudal fin truncate with attenuated margin edges, distinctly wider than remaining caudal region, I/11/I principal rays, principal central rays splitting once and dorsal and ventral principal rays splitting twice. Only first dorsal and ventral caudal-fin accessory rays visible. Anal and urogenital openings mid-way between pelvic fin base and anal-fin origin.

Free vertebrae 37. Ribs 13-14 pairs, first thickest, second to 12-13th pairs slightly longest, the last pair rudimentary and free. Dorsal pterygiophores 8, first in front of neural spine of 21th free vertebrae. Anal pterygiophores 6, first in front of haemal spine of 24th free vertebrae. Procurrent rays of dorsal lobe 14-16. Procurrent rays of ventral lobe 12-16. Caudal skeleton pleurostyle, hypurals 4+5, hypural 3, and fused parahypural and hypurals 1+2.

Color in alcohol: Refer to figures 2 for general view of color pattern in alcohol. Uniform gray on dorsal surface and sides of head, trunk and caudal peduncle, darker at nape. Dark stripe from eyes to anterior nostril. Elliptical, vertically elongated dark spot with illdefined borders at base of caudal fin. Few irregular spots on caudal peduncle in large specimens(48.9-54.3 mm SL) and on trunk and caudal peduncle in small (37.2-42.4 mm SL) specimens. Ventral surface of head and abdominal region without pigmentation. Dorsal surface of pectoral-fin base with few chromatophores, gradually scattered towards margin. Ventral surface of pectoral fin and pelvic fins unpigmented. Bases of dorsal and anal fin with chromatophores, more scattered towards margin over rays. Dorsal fin darker than anal fin. Chromatophores on base of caudal-fin rays, gradually more scattered towards margin. Nasal barbels with chromatophores all over their surface; maxillary barbels with chromatophores on their dorsal surface. Rictal barbels unpigmented. Internal surface of all barbels lighter than outer margin.

Distribution: Known only from the type-locality.

Etymology: Named after Dr. Miguel Trefaut Rodrigues, who discovered and collected the first specimens of the species.

Systematic and taxonomic comments: The genus Trichomycterushas been recognized as nonmonophyletic (Arratia, 1990, 1998, de Pinna, 1989; 1998), as is also true for the subfamily Trichomycterinae (de Pinna, 1989; 1998). Arratia (1990) proposed four “unique derived characters” for Trichomycterinae (1-“basioccipital”…” with well developed anterior membranous processes which lie ventrolateral to parasphenoid and prootics ”, 2-“an enarthrodial articulation between preopercle and opercle”…” is present in adults”, 3-“vomer with only one long posterior process”, and 4-“pronounced notch”…” on the posteroventral margin of ceratobranchial”). These features are present in all analyzed Trichomycterinae species prepared for C&S and X-ray, includingTrichomycterus trefauti ZBK . However, a more recent analysis (Costa & Bockmann, 1993) proposed Scleronema ZBK and the genus Ituglanis ZBK composed of species previously located in Trichomycterus , as two sequential monophyletic groups more related to the Glanapteryginae, Sarcoglanidinae, Tridentinae, Stegophilinae, and Vandelliinae, than to the other trichomycterine species. The lack of knowledge about the relationships among trichomycterine species, absence of definition of the genera Trichomycterus and Eremophilus ZBK , and the superficial definition of Hatcheria ZBK , Bullockia ZBK , Silvinichthys ZBK , and Rhizosomichthys ZBK make the allocation of new species difficult. Unfortunately, Trichomycterus has been considered as a group of species that do not possess the features present in other genera of trichomycterine. For this reason Trichomycterus has grown to a total of 96 nominal species (Barbosa & Costa, 2003; Fernández & Schaefer, 2003; de Pinna & Wosiacki, 2003; and Wosiacki & Garavello, 2004) in contrast with the other genera Eremophilus ZBK , Bullockia ZBK , Hatcheria ZBK , Rhizosomichthys ZBK , and Silvinichthys ZBK with only one species each.

The lack of pelvic fins and girdle has been used to diagnose Eremophilus ZBK , the only recognized distinction from Trichomycterus . These features were observed and discussed by Myers (1944), Miranda-Ribeiro (1949), de Pinna (1989, 1998), Costa & Bockmann (1993), Trajano & de Pinna (1996), Fernández & Vari (2000), and de Pinna & Wosiacki (2003). These papers have demonstrated that the lack of pelvic fins and girdle are highly homoplastic and for this reason, weak features to define a genus. Recently de Pinna & Wosiacki (2003) reallocated Eremophilus candidus Miranda-Ribeiro ZBK to the genus Trichomycterus ( T. candidus ) based on detailed phylogenetic analysis which indicates that it is more related to Trichomycterus species than to E. mutisii Humboldt ZBK . Arratia et al. (1978) proposed the genus Bullockia ZBK based on several features slightly similar to those of Hatcheria ZBK diagnosed in the same paper and in Arratia & Menu-Marques (1981). These features are clearly distinct from those observed in species of Trichomycterus . Characters like a narrow and strongly compressed caudal peduncle and a long dorsal fin with more than 17 rays are present in Hatcheria ZBK and Bullockia ZBK but are not present in species of Trichomycterus . Silvinichthys ZBK differs by having the entire surface of body skin perforated by pores of ampullary organs and a unique combination of characters (Arratia, 1998). Rhizosomichthys totae (Miles) is an atypical freshwater fish that has the unique character of thick fat tissue forming folds covering the entire body. Its osteology is unknown, and its relationship among trichomycterine is totally obscure.

Trichomycterus trefauti ZBK does not have the features above mentioned for Eremophilus ZBK , Bullockia ZBK , Hatcheria ZBK , Rhizosomichthys ZBK , and Silvinichthys ZBK and can not be allocated to any of these genera. In order to maintain nomeclatural stability it does not seem desirable to propose a new genus for one new species. It seems more parsimonious and coherent to allocate the new species in Trichomycterus .

The majority of the species of Trichomycterus are morphologically very similar to each other and the diagnosis of most species is only possible by a combination of several characters. Sometimes these features concern to internal anatomy and are difficult to analyze. Few species, like Trichomycterus castroi de Pinna ZBK , T. papilliferus Wosiacki & Garavello ZBK , T. trefauti ZBK have external autapomorphies that make them easy to identify Phylogenetic assignment and comparisons: The presence of stripes or bands in Trichomycteridae has been frequently recorded (e.g.,Scleronema operculatum (Eigenmann) ZBK , T. barbouri (Eigenmann) , T. castroi ZBK , T. itatiayae Miranda-Ribeiro ZBK , T. reinhardti (Eigenmann) , T. taeniops Fowler ZBK , T. taenia Kner ZBK ). A transverse band at the caudal fin has been recorded only in S. operculatum ZBK , T. castroi ZBK , and T. trefauti ZBK . The presence of a vertical caudal-fin band in T. castroi ZBK and S. operculatum ZBK was discussed by de Pinna (1992a) who interpreted these as autapomorphies for these species. The spot at the caudal-fin base of Trichomycterus trefauti ZBK has a different topology from the band of T. castroi ZBK that is at the distal margin of the caudal fin. In addition, the vertical spot at the caudal-fin base distinguishes T. trefauti ZBK from its sympatric congeners in the rio São Francisco basin ( T. brasiliensis Luetken ZBK , T. concolor Costa ZBK , T. itacarambiensis Trajano & Pinna ZBK , T. reinhardti , T. variegatus Costa ZBK ), and all other trichomycterins species. The spot at the caudal-fin base of T. trefauti ZBK is unique within trichomycterids and it is hypothesized to be an autapomorphy for this species.

The first pectoral-fin ray prolonged as a filament, present in T. trefauti ZBK , is present in all species of Ituglanis ZBK , Trichomycterus hasemani (Eigenmann) , T. johnsoni (Fowler) and several other species ( T. candidus , T. alternatus (Eigenmann) , T. punctulatus Valenciennes ZBK , T. brasiliensis ZBK , T. reinhardti , T. itacarambiensis ZBK , T. auroguttatus Costa ZBK , T. longibarbatus Costa ZBK , T. bahianus Costa ZBK , T. mimonha Costa ZBK , T. mirissumba Costa ZBK , T. itatiayae Miranda-Ribeiro ZBK , and T. immaculatus (Eigenmann & Eigenmann) ) among others. According to Costa & Bockmann (1993), Ituglanis ZBK is a monophyletic sister group of the Glanapteryginae, Sarcoglanidinae, Tridentinae, Stegophilinae, and Vandelliinae, and T. hasemani and T. johnsoni could be more closely related to other subfamilies (de Pinna, 1989). Therefore it is hypothesized that the first pectoral-fin rays prolonged as a filament is a homoplastic feature that has evolved several times in Trichomycteridae.

Ecology: The specimens were collected in a stream 2-4m wide, with an average depth of 10cm, and with a bottom of pebbles of variable size and rocks, at an elevation of approximately 1000m. The vegetation was of “campos rupestres”.


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