Taxonomic review of the genus Trichomycterus Valenciennes ( Siluriformes : Trichomycteridae ) from the laguna dos Patos system , Southern Brazil

The species of the genus Trichomycterus inhabiting the laguna dos Patos system are reviewed and five species are recognized. Trichomycterus tropeiro Ferrer & Malabarba has a restricted range and is endemic to the uppermost portion of the rio das Antas. Trichomycterus balios, n. sp., is distributed in the upper portion of the rio das Antas and rio Caí basins. Trichomycterus diatropoporos, n. sp., is endemic to the rio da Prata basin, a tributary of the rio das Antas. Trichomycterus poikilos, n. sp., is widely distributed in the upper portion of the rio Jacuí basin and tributaries of the rio Taquari-Antas. Trichomycterus brachykechenos, n. sp., is endemic to the upper portion of the rio dos Sinos. The new species are distinguishable from most congeners, except for T. davisi, T. mboycy, T. naipi, T. payaya, T. papilliferus, T. perkos, T. plumbeus, and T. tropeiro by the lower number of pectoral-fin rays (I+5-6) and by the first pectoral-fin ray not prolonged as a filament. Other characters distinguish the new taxa from these eight species. The distribution of the genus in the laguna dos Patos system is discussed and a taxonomic key is provided.

Despite the high number of described species within Trichomycterus, Ferrer & Malabarba (2011) highlighted the lack of taxonomic studies of this genus in the laguna dos Patos and Uruguay basins in southern Brazil.Notwithstanding the common occurrence of the genus in these basins, T. tropeiro Ferrer & Malabarba, 2011 endemic to the headwaters of rio das Antas in laguna dos Patos system is so far the only member of the genus recognized for that drainage.
In the present study the Trichomycterus in the laguna dos Patos system are reviewed through an extensive analysis of large collections of specimens.Four new species are recognized in addition to T. tropeiro.Comments on distributions and an identification key are given for the species of Trichomycterus from the laguna dos Patos system.

Material and Methods
Measurements were made point-to-point with digital calipers to the nearest 0.1 mm.The measurements follow Tchernavin (1944) for the length of barbels, Wosiacki & de Pinna (2008) for the length and depth of the caudal peduncle and for the supraorbital pore distance, Ferrer & Malabarba (2011) for the scapular girdle and Costa (1992) for the remaining measurements.
The nomenclature for osteological structures and laterosensory canal system and associated pores followed Bockmann et al. (2004).Vertebral counts exclude those in the Weberian complex and the compound caudal centrum (PU1+U1) is counted as one element.For osteological analysis, 30 specimens were cleared and counterstained (c&s) following the method proposed by Taylor & van Dyke (1985) and nine were disarticulated.The counts of unsegmented rays in c&s specimens are given before the number of unbranched and segmented rays (represented by upper case Roman numerals) and branched and segmented rays (represented by Arabic numerals), counted in all specimens.
Diagnosis.Trichomycterus balios is distinguishable from all congeners except T. davisi (Haseman, 1911); T. diatropoporos; T. papilliferus Wosiacki & Garavello, 2004  .9mm SL, some elements not shown.Abbreviations: AF, anterior fontanel; AN, antorbital; AP, autopalatine; EP, epioccipital; FR, frontal; LE, lateral ethmoid; i1, infraorbital sensory branch 1; i3, infraorbital sensory branch 3; i10-11, infraorbital sensory branch 10 and 11; ME, mesethmoid; MX, maxilla; PF, posterior fontanel; PM, premaxilla; po1-2, postotic sensory branches 1 and 2; PS, posttemporosupracleithrum; PT, pterotic; s1, supraorbital sensory branch 1; s3, supraorbital sensory branch 3; s6, supraorbital sensory branch 6 (epiphyseal branch); SO, tendon-bone supraorbital; SP+PO+PN, sphenoticprootic-pterosphenoid complex bone; SU, parieto-supraoccipital; WC, Weberian capsule.Scale bar = 2 mm.Garavello, 2004;and T. tropeiro by the modal possession of I+6 pectoral-fin rays (one among 108 specimens with I+7; vs. I+5, I+7, or more pectoral-fin rays) and the first ray of the pectoral fin not prolonged as a filament (Fig. 1;vs.the first ray of the pectoral fin prolonged as a filament).Trichomycterus balios is distinguished from T. davisi, T. diatropoporos, T. papilliferus, T. payaya, T. perkos, and T. plumbeus by the color pattern of the dorsal and lateral surfaces of body, which presents circular black blotches variable in size (Fig. 1;vs.the head and trunk with dark irregularly shaped spots scattered in T. davisi; lateral surface of body with dark blotches variable in size and shape progressively larger and coalescent dorsally thus forming extensive black pigmented regions with light yellow gaps in T. diatropoporos; dorsal and lateral surfaces of body pale brown to light gray in T. payaya; dorsal and lateral surfaces of body gray in T. papilliferus and T. plumbeus; lateral surface of body with three wide dark brown stripes in T. perkos).Trichomycterus balios is distinguished from T. tropeiro by the presence of the pelvic girdle and pelvic fins (Fig. 1;vs. absence); and the absence of pores i1 and i3 of the infraorbital sensory canal (Fig. 2a;vs. presence).Additionally, T. balios is distinguished from the remaining congeners in the laguna dos Patos system by the possession of 36-39 teeth on ceratobranchial 5 (Fig. 3a; vs. 12-13 in T. diatropoporos and 20-23 in T. poikilos); 35-40 teeth on plate connected to pharyngobranchial 4 (Fig. 3a;; by the color pattern of the dorsal and lateral surfaces of body with circular black blotches variable in size [Fig. 1;vs.the dorsal and lateral surfaces of body mottled dark brown over a light yellow background or with three stripes (dorsosagittal, midlateral, and ventrolateral) with notched borders in T. poikilos; the dorsal and lateral surface of body densely mottled dark brown over a light yellow background in T. brachykechenos].Trichomycterus balios is further distinguishable from T. poikilos by having the origin of the dorsal fin located at the vertical through the last third of the pelvic fin (Fig. 1;vs.at the vertical falling between the tip of the pelvic fin and the anterior insertion of anal fin).Trichomycterus balios is further distinguishable from T. brachykechenos by having a posterior cranial fontanel extending from the parieto-supraoccipital to the frontals (Fig. 2a; vs. the posterior cranial fontanel restricted to the parieto-supraoccipital); the maxillary barbel length (37.8-66.6% vs. 68.2-87.7%HL), the number of odontodes of the opercular patch (13-19 vs. 8-11).Trichomycterus balios is further distinguishable from T. diatropoporos by the insertion of the first dorsal-fin basal radial anterior to the neural spine of the 19 th -22 th vertebrae (vs.anterior to the neural spine of the 17 th or 18 th vertebrae).
Description.Morphometric data for holotype and paratypes in Table 1.Body elongate, trunk roughly cylindrical and gradually compressed towards caudal fin.Dorsal profile of trunk convex along anterior half then straight to insertion of dorsal fin.Ventral profile of trunk straight to slightly convex.Dorsal and ventral profile of caudal peduncle straight to slightly concave.
Head depressed, trapezoidal from dorsal view, wider posteriorly.Dorsal profile straight and ventral profile straight to slightly convex.Snout rounded from dorsal view.Eyes readily visible, anteroposteriorly elliptical to rounded, dorsally oriented; orbital rim not free, eyes covered with skin thin and transparent.Each eye located over posterior termination of shallow and small longitudinal crest beginning at posterior nostril and making eyes visible from lateral view.
Nostrils of same size and smaller than eye diameter.Anterior nostril surrounded by fleshy flap of integument posterolaterally continuous with nasal barbel.Posterior nostril surrounded anterolaterally by thin flap of integument.Gill openings not constricted but united with isthmus anteriorly forming a free fold.Mouth subterminal with corners posteriorly oriented.Lower lip with conspicuous fleshy lobes along lateral limits internal to origin of rictal barbels.Lips with small papillae; papillae largest on inner surface of upper lip.
Barbels with large bases and tapering gradually towards tip.Tip of nasal barbel usually reaching to between eye and pore i11 or at most slightly extending beyond pore i11.Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril.Maxillary barbel usually extending between anterior and posterior margins of interopercular patch of odontodes or at most slightly extending beyond to posterior margin but never reaching pectoral-fin insertion.Rictal barbel slightly shorter than maxillary barbel.
Mesethmoid with anterior margin slightly concave, cornua short and thick, width of their bases similar to their length (Fig. 2a).Anterior cranial fontanel restricted to small rounded opening situated between frontals and epiphyseal bar.Posterior cranial fontanel long and narrow, extending from posterior portion of frontals to parieto-supraoccipital. Epiphyseal bar longer than wide (absent in one of 14 specimens).Antorbital short and anteriorly expanded.Tendon-bone supraorbital elongate, approximately three times larger than antorbital, with process along distal margin.Anterior portion of sphenotic laterally directed from dorsal view.Sphenotic, prootic, and pterosphenoid totally fused.Vomer arrow-shaped with long posterior process extending to parasphenoid.Parasphenoid with long pointed process extending to basioccipital.Anterior portion of Weberian complex fused to basioccipital.Weberian capsule with lateral opening smaller than lateral profile of capsule.Premaxilla rectangular with 75-101 conical, curved and pointed teeth (n = 2).Teeth variable in size and distributed with some irregularity in up to four rows.Maxilla large, boomerang-shaped and shorter than premaxilla.Lower jaw with 89-107 conical, curved and pointed teeth variable in size (n = 2).Outer teeth row slightly flat vertically with blunt tips in largest specimens (greater than 85.4 mm SL).Teeth range from few teeth at base of coronoid process to four discernible rows near dentary symphysis.Autopalatine with anterior margin straight, mesial margin straight to slightly concave, distal margin slightly concave, and large posterior process extending to middle of metapterygoid.
Metapterygoid large and laminar and connecting with quadrate through cartilage.Hyomandibula well-developed.Preopercle long and narrow and in contact with ventral margins of quadrate and hyomandibula.Opercular patch of odontodes rounded with 13-19 conical odontodes (n = 14).Interopercular  Ventral hypohyal trapezoid-shaped (Fig. 4a).Anterior ceratohyal elongate and widening at anterior and posterior limits.Posterior ceratohyal short and triangular.Branchiostegal rays 8-9 (n = 14), usually 9, five on anterior ceratohyal, one on ceratohyal posterior and three articulated on interceratohyal cartilage.Last three branchiostegal rays widest.Dorsal hypohyal and interhyal absent.Urohyal with expanded anterior head, two elongate lateral processes with wide bases and decreasing in width distally with rounded tips and laminar, elongate, narrow posterior process (Fig. 5a).
Sensory canals on head with simple (non-dendritic) tubes ending in single pores (Fig. 2a).Supraorbital sensory canal complete with paired pores s1, s3 and s6.Pore s1 located between anterior nostrils, pore s3 located in same longitudinal row of pore s1 after posterior nostrils and pore s6 in interorbital space.Infraorbital sensory canal incomplete; pores i1 and i3 absent, pore i10 located behind eye and pore i11 located lateral to posterior margin of eye.Postotic pore po1 located lateral to anterior margin of opercular patch of odontodes.Postotic pore po2 located lateral to middle of length of opercular patch of odontodes.Lateral-line canal very short with 2 pores located above insertion of pectoral fin and just posterior of gill openings.
Pectoral fin with distal margin rounded, I+6* rays (1 of 108 specimens with I+7), first ray short and not prolonged as filament.Pelvic fin with distal margin rounded, reaching at most anterior margin of urogenital papilla, I+4 rays (n = 108).Inner margin of pelvic fins very close basally.Pelvic girdle with two basipterygia united medially by cartilage with two elongate bifid processes (external process and internal process) and medial process short (one of 14 specimens with medial process united to internal process).Pelvic splint thin, comma-shaped and parallel to first pelvic-fin ray.Urogenital papilla nearer tip of pelvic fin than origin of anal fin.
Coloration in alcohol.Dorsal and lateral surface of body with circular black blotches variable in size over light yellowish background; dark pigmentation more concentrated dorsally (Fig. 1).Ventral surface of body light yellow with diffuse small black spots laterally and between pectoral-fin insertions; spots larger and more concentrated between pelvic and anal fins and caudal peduncle.Dorsal surface of head with greater concentration of irregular black rounded blotches variable in size; blotches becoming more scattered on lateral surface, smaller ventrally and restricted to lateral and posterior margins of gill openings.Pectoral, dorsal, anal and caudal fins spotted basally, spotting becoming inconspicuous towards tips and margins lighter.Pelvic fin unpigmented.Barbels with dark pigmentation on both surfaces.Larger specimens (greater than 43.2 mm SL) with pigmentation arranged in two distinct layers; large rounded black spots on inner skin layer and small black spots on outer skin layer (Fig. 1).
Distribution and ecological notes.Trichomycterus balios is distributed in the upper portions of the rio das Antas and rio Caí tributaries to the laguna dos Patos system and in the   ;2,rio Caí;3,rio das Antas;3',4,rio da Prata;5,rio Carreiro;6,rio Guaporé;7,rio Forqueta;8,rio Pardo;9,rio Jacuí;10,laguna dos Patos;and 11,rio Mampituba basin.headwaters of the rio Mampituba (Fig. 8).The type locality is located at approximately 792 m a.s.l. and the remaining localities of collection between 681 and 941 m a.s.l.The lower portions of the laguna dos Patos system and of the rio Mampituba are widely separated by the rio Tramandaí drainage, were T. balios is unknow to occur (Malabarba et al., 2013).The occurrence of the species in the headwaters of these two unconnected and distant drainages (laguna dos Patos system and of the rio Mampituba) is possibly related to headwater capture events.
The localities where the types were collected had clear water with current water and rocky bottoms (Fig. 9a).Trichomycterus balios was collected with Cnesterodon brevirostratus Rosa & Costa, 1993; Pareiorhaphis hystrix (Pereira & Reis, 2002); and Bryconamericus patriciae da Silva, 2004 at the type locality, other species that show some degree of endemism in the region associated with high altitudes (Rosa & Costa, 1993;Pereira & Reis, 2002, da Silva, 2004).The stomach of 13 c&s specimens contained larvae of Diptera (Chironomidae, Simuliidae), Lepidoptera, and Trichoptera; and nymphs of Ephemeroptera and Plecoptera.
Remarks.The type series includes only specimens from laguna dos Patos system.Data of specimens from the rio Mampituba identified as T. balios are not included in the species description.
Etymology.From the Greek balios meaning spotted, in reference to the color pattern of the new species formed by circular black blotches.An adjective.

Diagnosis.
Trichomycterus diatropoporos is distinguishable from all congeners except T. balios, T. davisi, T. papilliferus, T. payaya, T. perkos, T. plumbeus, and T. tropeiro by the possession of I+6 pectoral-fin rays (vs.I+5, I+7, or more) and the first ray of the pectoral fin not prolonged as a filament (Fig. 10; vs. the first ray of the pectoral fin prolonged as a filament).is further distinguishable from T. tropeiro by the presence of the pelvic girdle and pelvic fins (Fig. 10; vs. absence); and the insertion of the first dorsal-fin basal radial anterior to neural spine of 17 th or 18 th vertebrae (vs.anterior to neural spine of 19 th -20 th vertebrae).
Description.Morphometric data for holotype and paratypes in Table 2. Body elongate, trunk roughly cylindrical and gradually compressed towards caudal fin.Dorsal profile of trunk convex along anterior half then straight to insertion of dorsal fin.Dorsal profile of caudal peduncle straight to slightly convex.Ventral profile of trunk and caudal peduncle nearly straight.Head depressed, trapezoidal from dorsal view, wider posteriorly.Dorsal profile of head straight and ventral profile straight to slightly convex.Snout rounded from dorsal view.Eyes readily visible, anteroposteriorly elliptical and dorsally oriented, orbital rim not free, eyes covered with skin thin and transparent.Each eye located over posterior termination of small longitudinal ridge beginning at posterior nostril and making eyes fully visible from lateral view.
Nostrils of same size and smaller than diameter of eye.Anterior nostril surrounded by fleshy flap of integument posterolaterally continuous with nasal barbel.Posterior nostril surrounded anterolaterally by thin flap of integument.Gill openings not constricted but united with isthmus anteriorly forming a large free fold.Mouth subterminal, corners posteriorly oriented.Lower lip with conspicuous fleshy lobes along lateral limits internal to origin of rictal barbels.Lips with small papillae; papillae largest on inner surface of upper lip.
Barbels with large bases and tapering gradually towards tip.Tip of nasal barbel usually reaching to between eye and pore i11 or at most slightly extending beyond pore i11.Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril.Maxillary barbel usually extending posteriorly to between anterior margin of interopercular patch of odontodes and middle of patch but never reaching posterior margin of patch.Rictal barbel slightly shorter than maxillary barbel.
Mesethmoid with anterior margin slightly concave, cornua short and thick, width of their bases similar to their length (Fig. 2b).Anterior cranial fontanel restricted to small rounded opening situated between frontals and epiphyseal bar.Posterior cranial fontanel narrow and long extending from posterior portion of frontals to parieto-supraoccipital. Epiphyseal bar longer than wide.Antorbital short and anteriorly expanded.Tendon-bone supraorbital elongate, approximately three times larger than antorbital.Anterior portion of sphenotic anterolaterally directed from dorsal view.Sphenotic, prootic and pterosphenoid totally fused.Vomer arrow-shaped with long posterior process extending to parasphenoid.Parasphenoid with long pointed process extending to basioccipital.Anterior portion of Weberian complex fused to basioccipital.Weberian capsule with lateral opening smaller than lateral profile of capsule.
Premaxilla rectangular with 103 conical, curved and pointed teeth (n = 1).Teeth variable in size and irregularly distributed in up to three rows.Maxilla large, boomerang-shaped and shorter than premaxilla.Lower jaw with 75 conical to slightly vertically flat, curved and pointed teeth of variable size (n = 1).Few teeth at base of coronoid process and up to three discernible rows near dentary symphysis (Fig. 11a).
Autopalatine with anterior margin convex, mesial margin concave, distal margin slightly concave and small posterior process extending slightly over metapterygoid.Metapterygoid large, laminar and connecting with quadrate through cartilage.Hyomandibula well-developed.Preopercle long and narrow and in contact with ventral margins of quadrate and hyomandibula.Opercular patch of odontodes rounded with 13-19 conical odontodes (n = 4).Interopercular patch of odontodes elongate with 20-23 conical odontodes (n = 4) more concentrated posteriorly.Odontodes of both opercular and interopercular patches gradually curving medially and increasing in size posteriorly.
Ventral hypohyal trapezoidal (Fig. 4b).Anterior ceratohyal elongate and widening at anterior and posterior limits.Posterior ceratohyal short and triangular.Nine branchiostegal rays (n = 4); five on anterior ceratohyal, one on posterior ceratohyal and three on interceratohyal cartilage.Last three branchiostegal rays widest.Dorsal hypohyal and interhyal absent.Urohyal with expanded anterior head, two elongate lateral processes with wide bases and decreasing in width distally and bearing rounded tips; and laminar, elongate, narrow posterior process (Fig. 5b).
Sensory canals on head with simple (non-dendritic) tubes ending in single pores (Fig. 2b).Supraorbital sensory canal complete with pores s1, s3 and s6.Pore s1 located between  anterior nostrils; pore s3 located in a longitudinal line passing through pore s1, after posterior nostrils, and pore s6 in interorbital space.Infraorbital sensory canal incomplete; presence of pores i1 and i3 variable (present in 8 specimens, including holotype and absent in 17 specimens); when present located beside nostrils.Pore i10 located behind eye.Pore i11 located laterally to posterior margin of eye.Postotic pore po1 located lateral to anterior margin of opercular patch of odontodes.Postotic pore po2 located lateral to middle of opercular patch of odontodes.Lateral-line very short with 2 pores located above insertion of pectoral fin and just posterior to gill openings.
Pectoral fin with distal margin truncate to slightly rounded, I+6 rays (n = 25), first ray short and not prolonged as filament.Pelvic fin with distal margin rounded reaching at most anterior margin of urogenital papilla, I+4* rays (1 of 25 specimens with I+3).Inner margin of pelvic fins very close basally and sometimes in contact.Pelvic girdle with two basipterygia united medially by cartilage with two elongate bifid processes (external process and internal process) and medial process short (Fig. 12).Pelvic splint thin, comma-shaped, and parallel to first pelvic-fin ray.Urogenital papilla nearer tip of pelvic fin than anal-fin origin.
Anal fin slightly smaller than dorsal fin with distal margin rounded, two or three unsegmented rays (n = 4), II+5 (n = 25).Anal-fin origin located at vertical through base of last dorsalfin ray.Anal-fin basal radials 6 (n = 4); first inserting anterior to haemal spine of 21 th or 22 th vertebrae.

Coloration in alcohol.
Lateral surface of body covered with dark blotches variable in size and shape over light yellow background (Fig. 10).Blotches progressively larger and coalescent dorsally thus forming extensive black pigmented regions with light yellow gaps.Ventral surface of body yellow on trunk with irregular black blotches between pelvic and anal fins and on caudal peduncle.Dorsal and lateral surface of head black with small lighter areas; ventral surface yellow.Pectoral, dorsal, anal and caudal fins spotted with irregular black marks and lighter along margins.Pelvic fin unpigmented.Barbels with dark pigmentation dorsally and yellow ventrally.Larger specimens (greater than 57.4 mm SL) with pigmentation arranged in two distinct layers; dark blotches variable in size and shape on inner skin layer and small black spots on outer skin layer more evident in caudal peduncle.Distribution and ecological notes.Trichomycterus diatropoporos is apparently endemic to the rio da Prata and rio Turvo basins, tributaries of rio das Antas, in the laguna dos Patos system (Fig. 8).At the type locality the rio da Prata is a rapid flowing, wide and shallow, with an average depth of 0.5 m, with clear water, rocky bottom and large amounts of submerged vegetation (Carvalho & Reis, 2011) (Fig. 9b).It is upstream of a waterfall known as Cascata da Usina at approximately 660 m a.s.l.At this site T. diatropoporos occurs sympatrically with Hisonotus prata Carvalho & Reis, 2011, another endemic species to the rio da Prata.The other two localities of the paratypes are located at approximately 642 m and 825 m a.s.l.The stomach of three c&s specimens contained larvae of Diptera (Chironomidae, Simuliidae) and nymphs of Ephemeroptera.
Remarks.The presence of the infraorbital sensory canal is variable among the specimens of T. diatropoporos, even in specimens from same lot and of the same size (e.g., MCP 40933).Although characters related to the reduction of the sensory canal have been used in defining species and even genera in the Trichomycterinae (see Arratia, 1998), there are no additional detectable differences in morphometrics, meristics data and coloration pattern among specimens bearing or lacking pores i1 and i3 of infraorbital sensory canal to justify the recognition of two different species.Apparently, this variation in the presence of pores i1 and i3 of infraorbital sensory canal is unique among species of Trichomycterus.One specimen (MCP 22785) also from rio da Prata basin with counts, morphometrics, and color pattern similar to T. diatropoporos lacks pelvic fins and was not included in type-series.The specimen definitely is not T. tropeiro, the species from laguna dos Patos system that consistently lacks pelvic fins, but rather appears to be an anomalous individual of T. diatropoporos.Among other trichomycterines, intraspecific variation in the presence/absence of pelvic fins is also known in Ituglanis parahybae (Eigenmann, 1918) (Costa & Bockmann, 1993).
Etymology.From the Greek diatropos meaning variable, and poros meaning pore, in reference to the variation in the presence of pores i1 and i3 of infraorbital sensory canal of the new species.A noun in apposition.Diagnosis.Trichomycterus poikilos is distinguishable from all congeners except T. brachykechenos; T. mboycy Wosiacki & Garavello, 2004;and T. naipi Wosiacki & Garavello, 2004 by the modal possession of I+5 pectoral-fin rays (one among 82 specimens with I+6; vs. I+6 or more pectoral-fin rays) and the first ray of the pectoral fin not prolonged as a filament (Figs.13-14; vs. the first ray of the pectoral fin prolonged as a filament).Trichomycterus poikilos is distinguished from T. brachykechenos by having the posterior fontanel extending from the parieto-supraoccipital to the frontals (Fig. 2c; vs. the posterior cranial fontanel restricted to the parietosupraoccipital), the origin of dorsal fin located at the vertical falling between the tip of the pelvic fin and the anterior insertion of the anal fin (Figs.13-14; vs. the origin of dorsal fin located at the vertical through the last third of the pelvic fin), the maxillary barbel length (33.2-60.4% vs. 68.2-87.7%HL), and the number of odontodes of the opercular patch (13-17 vs. 8-11).Trichomycterus poikilos is distinguished from T. mboycy by the pectoral-fin length (7.7-9.1% vs. 9.9-13.8%SL) and skin color (Figs.[13][14]; yellow background vs. gray background); and from T. naipi in the number of odontodes of the interopercular patch (20-32 vs. 12-15), number of dorsal-fin rays (I-II+6-7 vs. I+8), and absence of a thin unpaired dark dorsosagittal body stripe in larger specimens (Fig. 13; vs. presence of a thin unpaired dark dorsosagittal stripe in larger specimens).Additionally, T. poikilos is distinguished from remaining congeners in the laguna dos Patos system by having the origin of the dorsal fin located at the vertical falling between the tip of the pelvic fin and the anterior insertion of the anal fin (Figs.[13][14]; vs. at the vertical through the last third of the pelvic fin in T. balios and T. diatropoporos); 20-23 teeth on ceratobranchial 5 (Fig. 3c;  Description.Morphometric data for holotype and paratypes in Table 3. Body elongate, trunk roughly cylindrical and gradually compressed towards caudal fin.Dorsal profile of trunk convex along anterior half, then straight to insertion of dorsal fin.Ventral profile of trunk straight to slightly convex.Dorsal and ventral profile of caudal peduncle straight.Head depressed, trapezoidal from dorsal view, wider posteriorly.Dorsal profile straight and ventral profile straight to slightly convex.Snout rounded from dorsal view.Eyes readily visible, anteroposteriorly elliptical and dorsally oriented; orbital rim not free, eyes covered with skin thin and transparent.Each eye located over posterior termination of shallow small longitudinal crest beginning at posterior nostril and making eyes visible from lateral view.
Nostrils of same size and smaller than diameter of eye.Anterior nostril surrounded by fleshy flap of integument posterolaterally continuous with nasal barbel.Posterior nostril surrounded anterolaterally by thin flap of integument.Gill openings not constricted but united with isthmus anteriorly forming a free fold.Mouth subterminal with corners posteriorly oriented.Lower lip with conspicuous fleshy lobes along lateral limits internal to origin of rictal barbels.Lips with small papillae; papillae largest on inner surface of upper lip.
Barbels with large bases and tapering gradually towards tips.Tip of nasal barbel usually reaching to between pore i11 and pore po1 or at most to middle of distance between them.Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril.Maxillary barbel usually extending between to anterior and posterior margins of interopercular patch of odontodes.Rictal barbel slightly shorter than maxillary barbel.
Mesethmoid with anterior margin slightly concave, cornua short and thick, width of their bases similar to their length (Fig. 2c).Anterior cranial fontanel restricted to small rounded opening situated between frontals and epiphyseal bar.Posterior cranial fontanel long and narrow extending from posterior portion of frontals to parieto-supraoccipital. Epiphyseal bar longer than wide.Antorbital short and anteriorly expanded.Tendon-bone supraorbital elongate, anteriorly expanded and approximately three times larger than antorbital.Anterior portion of sphenotic anterolaterally directed from dorsal view.Sphenotic, prootic and pterosphenoid totally fused.Vomer arrow-shaped with long posterior process extending to parasphenoid.Parasphenoid with long and pointed process extending to basioccipital.Anterior portion of Weberian complex fused to basioccipital.Weberian capsule with lateral opening smaller than lateral profile of capsule.
Premaxilla rectangular with 74-76 curved, flat vertically to slightly conical and blunt teeth (n = 3).Teeth of variable size, irregularly distributed in three rows.Maxilla large, boomerangshaped and shorter than premaxilla.Lower jaw with 79-91 curved, flat vertically and blunt teeth of variable size (n =3).Few teeth at base of coronoid process and three discernible rows near dentary symphysis (Fig. 11b).Autopalatine with anterior and mesial margins straight, distal margin straight to slightly concave and small posterior process extending slightly over metapterygoid.
Metapterygoid large and laminar and connecting with quadrate through cartilage.Hyomandibula well-developed.Preopercle long and narrow and in contact with ventral margins of quadrate and hyomandibula.Opercular patch of odontodes rounded with 13-17 conical odontodes (n = 9).Interopercular patch of odontodes elongate with 20-32 conical odontodes (n = 9) more concentrated posteriorly.Odontodes of both opercular and interopercular patches gradually curving medially and increasing in size posteriorly.
Ventral hypohyal triangular (Fig. 4c).Anterior ceratohyal elongate and widening at anterior and posterior limits.Posterior ceratohyal short and triangular.Nine branchiostegal rays (eight in one side of 1 specimen) (n = 9); five on anterior ceratohyal, one on posterior ceratohyal and three on interceratohyal cartilage.Last four branchiostegal rays widest.Dorsal hypohyal and interhyal absent.Urohyal with expanded anterior head; two elongate lateral processes with wide bases narrowing distally and bearing rounded tips; and laminar, elongate, narrow posterior process (Fig. 5c).
Sensory canals on head with simple (non-dendritic) tubes ending in single pores.Supraorbital sensory canal complete with pores s1, s3 and s6 (Fig. 2c).Pore s1 located between anterior nostrils, pore s3 located in same longitudinal row of pore s1 after posterior nostrils and pore s6 in interorbital space.Infraorbital sensory canal incomplete; pores i1 and i3 absent, pore i10 located behind eye and pore i11 located lateral to posterior margin of eye.Postotic pore po1 located lateral to anterior margin of opercular patch of odontodes.Postotic pore po2 located lateral to middle of length of opercular patch of odontodes.Lateral-line very short with 2 pores located above insertion of pectoral fin and just posterior of gill openings.
Pectoral fin with distal margin rounded, I+5* rays (1 of 82 specimens with I+6), first ray short and not prolonged as filament.Pelvic fin with distal margin rounded reaching at most anterior margin of urogenital papilla, I+4* rays (1 of 82 specimens with I+3).Inner margin of pelvic fins very close basally.Pelvic girdle with two basipterygia united medially by cartilage with two elongate bifid processes (external process and internal process) and medial process short (in two of eight specimens medial process united to internal process).Pelvic splint thin, commashaped and parallel to first pelvic-fin ray.Urogenital papilla nearer tip of pelvic fin than origin of anal fin.
Dorsal fin with distal margin rounded, semicircular when fin expanded with one to three unsegmented rays (n = 9), I-II+6-7 rays (n = 82), usually II+7*.Dorsal-fin origin located at vertical between tip of pelvic fin and anterior insertion of anal fin, usually in the papillae urogenital.Dorsal-fin basal radials 7-8 (n = 9); first inserting anterior to neural spine of 20 th to 22 th vertebrae.

Coloration in alcohol.
Trichomycterus poikilos demonstrates a variable color pattern.Most of types present the dorsum and lateral surface of body mottled dark brown over a light yellow background (Fig. 13 and 14a).Some specimens have a wide unpaired dorsosagittal stripe and midlateral and ventrolateral bilaterally paired stripes with notched borders (Fig. 14c).Smallest specimens with midlateral stripe more evident and ventrolateral stripe diffuse (Fig. 14d and 14e).Ventral surface of body light yellow with diffuse and small black spots between pectoral-fin insertion and near pelvicfin insertion.Area between pelvic and anal fins and caudal peduncle mottled dark brown over light yellow background.Head dark brown mottled over light yellow background dorsally and yellow ventrally.Pectoral, dorsal, anal and caudal fins spotted basally with dark pigmentation becoming inconspicuous towards tips, and lighter along margins.Pelvic fin unpigmented.Barbels with dark pigmentation dorsally and lighter ventrally.Large specimens (greater than 46.6 mm SL) with pigmentation arranged in two distinct layers; mottled dark brown or with three stripes (dorsosagittal, midlateral, and ventrolateral) with notched borders on inner skin layer and small black spots on outer skin layer (Fig. 13, 14a-c).
Distribution and ecological notes.Trichomycterus poikilos is distributed in the rio Jacuí, rio Pardo and rio Taquari-Antas basins, in the laguna dos Patos system (Fig. 8).The species is widely distributed in the upper portion of rio Jacuí basin, occurring at elevations of 124 to 700 m a.s.l.One lot is from the headwaters of rio Pardo basin, at 625 m a.s.l.In the Taquari-Antas basin the species occurs in the upper portions of the Carreiro, Guaporé, and Forqueta rivers, between 417 and 688 m a.s.l.The type locality is a rapid flow river with clear water, a rocky bottom and submerged vegetation (Fig. 9c), located at approximately 405 m a.s.l.At this site the specimens were associated with submerged vegetation and collected with Ancistrus brevipinnis (Regan, 1904), Eurycheilichthys limulus Reis &Schaefer, 1998, andRineloricaria cadeae (Hensel, 1868).The stomach of six c&s specimens contained aquatic larvae of Diptera (Simuliidae) and Lepidoptera; and nymphs of the Ephemeroptera and Plecoptera.
Remarks.Trichomycterus poikilos demonstrates intraspecific ontogenetic color pattern variation.Although Bockmann & Sazima (2004) considered the body pigmentation pattern highly conserved in known species of Trichomycterus, a intraspecific variation in coloration is present in T. caipora Lima, Lazzarotto & Costa, 2008(Lima et al., 2008), in T. iheringi (Eigenmann, 1917) associated to body size and microhabitat preference (da Silva et al., 2010), and in T. santanderensis Castellanos-Morales, 2007.The ontogenetic variation in T. poikilos is clear in lot UFRGS 14992 (six specimens with 40.5-92.5 mm SL), in which the smallest specimens have one obvious midlateral stripe on the body that gradually become indistinguishable in the largest specimens (Fig. 14).This ontogenetic variation is not observed in all samples.In other lots all specimens have a mottled pattern (UFRGS 14500, 11 specimens with 32.0-74.5 mm SL) regardless of body size.Besides coloration no additional differences were found between these populations that allow us to separate them and ontogenetic variation in the color pattern seems to appear only in some populations.
Seven specimens from the rio do Sinos basin are poorly preserved and were not measured or counted (MCP 26148), however a mottled color pattern over a light yellow background is present in all specimens, and one c&s specimen possesses the lower jaw with blunt teeth which leads us to believe it to be T. poikilos.

Etymology.
From the Greek poikilos meaning variegated, varicolored, in reference to the intraspecific color pattern variation of the new species.An adjective.

Diagnosis. Trichomycterus brachykechenos is distinguishable from all congeners except T. megantoni
Fernández & Chuquihuamaní, 2007 by its elongate posterior cranial fontanel which is restricted to the parietosupraoccipital (Fig. 2d vs. the posterior fontanel extending from the parieto-supraoccipital to the frontals or posterior fontanel separated in two openings not restricted to the parieto-supraoccipital). Trichomycterus brachykechenos is distinguished from T. megantoni by the modal possession of I+5 pectoral-fin rays (one among 15 specimens with I+6 vs. I+7-8 pectoral-fin rays), first ray of the pectoral fin not prolonged as a filament (Fig. 15; vs. the first ray of the pectoral fin prolonged as a filament), absence of the interopercle thickened ventrally (vs.presence).Trichomycterus brachykechenos is further distinguishable from all its congeners except T. mboycy, T. naipi, and T. poikilos by the modal possession of I+5 pectoral-fin rays (one among 15 specimens with I+6; vs. I+6 or more pectoralfin rays) and the first ray of the pectoral fin not prolonged as a filament (Fig. 15;vs.first ray of the pectoral fin prolonged as a filament).Trichomycterus brachykechenos is further distinguishable from T. mboycy and T. naipi by the color pattern of the dorsal and lateral surface of body of a densely mottled dark brown over a light yellow background (Fig. 15; vs. the lateral surface of body with small spots in T. mboycy; the lateral surface of body with three dark longitudinal stripes in T. naipi); the maxillary barbel length (68.2-87.7% vs. 50.3-63%HL in T. mboycy; 34.1-68.2%HL in T. naipi).Additionally, T. brachykechenos is distinguished from the remaining congeners in the laguna dos Patos system by the number of odontodes on the opercular patch (8-11 vs. 13 or more in T. balios, T. diatropoporos, T. poikilos, and T. tropeiro) and the maxillary barbel length (68.2-87.7% vs. 37.8-66.6%HL in T. balios; 38.3-53.9%HL in T. diatropoporos; 33.2-60.4% HL in T. poikilos).
Description.Morphometric data for holotype and paratypes in Table 4. Body elongate, trunk roughly cylindrical and gradually compressed towards caudal fin.Dorsal profile of trunk convex along anterior half then straight to insertion of dorsal fin.Ventral profile of trunk straight.Dorsal and ventral profiles of caudal peduncle slightly concave to straight.Head depressed, trapezoidal to square in larger specimens from dorsal view, wider posteriorly.Dorsal profile straight and ventral profile straight to slightly convex.Snout rounded from dorsal view.Eyes readily visible, rounded and dorsally oriented, orbital rim not free, eyes covered with skin thin and transparent.Each eye located over posterior termination of shallow and small longitudinal crest beginning at posterior nostril and making eyes visible from lateral view.
Nostrils of same size and smaller than diameter of eye.Anterior nostril surrounded by fleshy flap of integument posterolaterally continuous with nasal barbel.Posterior nostril surrounded anterolaterally by thin flap of integument.Gill opening not constricted but united with isthmus anteriorly forming a free fold.Mouth subterminal with corners posteriorly oriented.Lower lip with conspicuous fleshy lobes along lateral limits internal to origin of rictal barbels.Lips with small papillae; papillae largest on inner surface of upper lip.
Barbels with large bases and tapering gradually towards tips.Tip of nasal barbel usually reaching opercular patch of odontodes, always to middle of distance between pore i11 and pore po1.Origin of nasal barbels on posterolateral portion of integument flap around anterior nostril.Maxillary barbel usually reaching or extending beyond pectoral-fin insertion, always extending beyond posterior margin of interopercular patch of odontodes.Rictal barbel slightly shorter than maxillary barbel.
Mesethmoid with anterior margin slightly concave to straight, cornua short and thick, width of their bases similar to their length.Anterior cranial fontanel absent or restricted to very small opening situated between frontals (Fig. 2d).Epiphyseal bar absent.Posterior cranial fontanel elongate and restricted to parieto-supraoccipital. Antorbital short and anteriorly expanded.Tendon-bone supraorbital elongate and rod-like shaped.Anterior portion of sphenotic directed anteriorly from dorsal view.Sphenotic, prootic and pterosphenoid totally fused.Vomer arrow-shaped with long posterior process extending to parasphenoid.Parasphenoid with long and pointed process extending to basioccipital.Anterior portion of Weberian complex fused to basioccipital.Weberian capsule with lateral opening smaller than lateral profile of capsule.
Premaxilla rectangular with 78 conical, curved and pointed teeth (n = 1).Teeth of variable size and irregularly distributed in up to three rows.Maxilla large, boomerang-shaped and shorter than premaxilla.Lower jaw with 75 conical, curved and pointed teeth of variable size (n = 1).Few teeth at base of coronoid process and three discernible rows near dentary symphysis.Autopalatine with anterior margins straight, mesial and distal margins concave and small posterior process (Fig. 16) extending slightly over metapterygoid.
Metapterygoid large and laminar and connecting with quadrate through cartilage.Hyomandibula well-developed.Preopercle long and narrow and in contact with ventral margins of quadrate and hyomandibula.Opercular patch of odontodes rounded with 8-11 conical odontodes (n = 2).Interopercular patch of odontodes elongate with 22-30 conical odontodes (n = 2) more concentrated posteriorly.Odontodes of both opercular and interopercular patches gradually curved medially and increasing in size posteriorly.
Basibranchial 1 absent.Basibranchials 2 and 3 connected to each other, of approximately equal lengths with cartilage at tips (Fig. 3d).Ossified portion of basibranchial 2 distinctly wider than basibranchial 3. Basibranchial 4 completely cartilaginous.Hypobranchial 1 of similar size as but narrower than basibranchial 2 with cartilage at tips.Hypobranchials 2 and 3 with narrow ossified portion anterolaterally, larger on hypobranchial 2, and large area of cartilage distally; cartilage larger in hypobranchial 3. Hypobranchial 4 absent.Five elongate and narrow ceratobranchials with cartilage at tips.Ceratobranchials 2 and 3 with concavity along posterior margins; concavity larger in ceratobranchial 3. Ceratobranchial 5 expanded posteromedially with 21-22 conical, elongate and pointed teeth arranged in 3 rows (n = 1).Five epibranchials; first three elongate and narrow with cartilage at tips.Epibranchials 1 and 2 with triangular process along anterior margins; process slightly larger in epibranchials 1. Epibranchial 3 with robust uncinate process along posterior margin.Epibranchial 4 rectangular.Epibranchial 5 small and completely cartilaginous.Pharyngobranchials 1 and 2 absent.Pharyngobranchial 3 similar in form but shorter than hypobranchial 1 with cartilage at tips.Pharyngobranchial 4 curved and well ossified connected to plate with 22-25 conical, elongate and pointed teeth arranged in 3 rows; teeth growing in length posteriorly (n = 1).
Sensory canals on head with simple (non-dendritic) tubes ending in single pores.Supraorbital sensory canal complete with pores s1, s3 and s6.Pore s1 located between anterior nostrils, pore s3 located in same longitudinal row of pore s1 after posterior nostrils and pore s6 in interorbital space.Infraorbital sensory canal incomplete; pores i1 and i3 absent, pore i10 located behind the eye and pore i11 located lateral to posterior margin of eye.Postotic pore po1 located lateral to anterior margin of opercular patch of odontodes.Postotic pore po2 located lateral to middle of length of opercular patch of odontodes.Lateral-line very short with 2 pores and located above insertion of pectoral fins and just posterior of gill openings.
Pectoral fin with distal margin rounded to truncate, I+5* (1 of 15 specimens with I+6), first ray short and not prolonged as filament.Pelvic fin with distal margin rounded reaching at most anterior margin of urogenital papillae, I+4* (one specimen with I+3) (n = 15).Inner margin of pelvic fin very close basally.Pelvic girdle with two basipterygia united medially by cartilage with two elongate bifid processes (external process and internal process) and medial process short.Pelvic splint thin, comma-shaped and parallel to first pelvic-fin ray.Urogenital papillae nearer tip of pelvic fin than origin of anal fin.
Coloration in alcohol.Dorsal and lateral surfaces of head and body densely mottled dark brown over a light yellow background and progressively lighter ventrally (Fig. 15).Ventral surface of head and trunk yellow.Area between pelvic and anal fins and ventral surface of caudal peduncle light brown.Pectoral, dorsal, anal, and caudal fins weakly pigmented with small light brown spots and lighter along margins.Pelvic fin unpigmented.Barbels with dark pigmentation dorsally and lighter ventrally.
Distribution and ecological notes.Trichomycterus brachykechenos is apparently endemic to the rio do Sinos, in the laguna dos Patos system (Fig. 8).At the locality where most types (11 specimens) were collected, the rio do Sinos is narrow (ranging from 5 to 9 m a.s.l.) and shallow (depth less to 1 m) with fast current and rapids, a distinct slope, clear waters, a substrate consisting mainly of large rocks, and conserved riparian vegetation (Fig. 9d).The type locality is located at elevation of approximately 109 m a.s.l. and the two other type lots were from 169 m and 266 m a.s.l.The stomach contents of one c&s specimen contained larvae of the Chironomidae (Diptera) and pupa of the Diptera.
In the Trichomycterus species the cranial fontanel is normally divided in two openings separated by epiphyseal bar: the anterior fontanel which is a small rounded opening situated between frontals, and the posterior fontanel which is long and narrow extending from posterior portion of frontals to parieto-supraoccipital.A reduced cranial fontanel is present in at least other three species of the genus: T. cachiraensis Ardila Rodríguez, 2008, T. sketi Castellanos-Morales, 2011 from Colombia, and T. megantoni from Peru.
The cranial fontanel of Trichomycterus megantoni is illustrated and described as "reduced between frontals and supraoccipital" (Fernández & Chuquihuamaní, 2007: fig.3), a shape very similar to T. brachykechenos, which is absent or restricted to a very small opening anteriorly and elongate and restricted to the parieto-supraoccipital posteriorly (Fig. 2d).Fernández & Chuquihuamaní (2007) stated that the peculiar cranial fontanel of Trichomycterus megantoni is probably an autopomorphy, but cannot be ascertained as unique in Trichomycterinae because some species are rare or do not have their anatomy examined.Indeed, the discovery of T. brachykechenos confirms that the condition is not unique in the subfamily Trichomycterinae.
Nevertheless, the several differences between the two species (see diagnosis) lead us to believe that they are not closely related and that this reduction is homoplastic among the two species.It reinforces the assumption of Fernández & Chuquihuamaní (2007) that cranial fontanel reduction must be interpreted as homoplastic among Trichomycterus species, Ituglanis, glanapterygines and stegophilines, according to the current understanding of the trichomycterid phylogeny.
Etymology.From the Greek brachys meaning short, and kechenos meaning gap, opening, in reference to the short posterior cranial fontanel of the new species.A name in apposition.
The four new species present 10 of 11 synapomorphies that support the clade 2 (sensu de Pinna, 1998 andupdated in Bockmann, et al., 2004), which is formed by all trichomycterids except Copionodontinae and Trichogeninae: sphenotic, prootic, and pterosphenoid fused; incomplete infraorbital branch of laterosensory canal system; Weberian capsule with a small lateral opening, much smaller than its lateral profile; interhyal absent; five or fewer pelvic-fin rays; the anterior cranial fontanel partially or completely closed; a dorsal caudalfin plate with six or fewer rays; a ventral caudal-fin plate with eight or fewer rays; a dorsal caudal-fin lobe with five or fewer branched rays; and a ventral caudal-fin lobe with six or fewer branched rays.Two other synapomorphies reported for this clade were not evaluated in the current study: the presence of the protractor operculi muscle (de Pinna, 1992a(de Pinna, , 1998;;Datovo & Bockmann, 2010) and the fibers of the levator operculi being posterodorsally directed towards its origin (Datovo & Bockmann, 2010).
In the few studies that attempted to elucidate the relationships among the species of Trichomycterus of south and southern of Brazil, Wosiacki & de Pinna (2008) recognized a monophyletic group formed by the species endemic to the rio Iguaçu basin [T.crassicaudatus Wosiacki & de Pinna, 2008; T. igobi Wosiacki &de Pinna, 2008, andT. stawiarski (Miranda Ribeiro, 1968)] based in three putative synapomorphies: the procurrent caudal-fin rays thickly ossified and rigid, the dorsal procurrent rays extend for a long portion of the caudal peduncle, stretching over the tips of at least ten neural spines, and 10-11 branchiostegal rays.Datovo et al. (2012) confirmed the validity of these characters and tentatively proposed another species from rio Paraná basin, Trichomycterus perkos, as the sister-group of the clade T. crassicaudatus, T. igobi, and T. stawiarski based on the share of the third character (10-11 branchiostegal rays).However, none of these three features are present in the species described herein from the laguna dos Patos system.
Another attempt to define a monophyletic group within Trichomycterinae is the case of Trichomycterus brasiliensis species-complex, proposed initially by Costa (1992) based in the proximity of the bases of pelvic fins, distal border of caudal fin rounded, and irregular confluent marks on lateral surface of body.This species-complex was redefined by Barbosa & Costa (2003) mentioning three morphometric synapomorphies, latter contested by Bockmann & Sazima (2004) due the lack of clear landmarks for precise comparisons.Thus, the T. brasiliensis species-complex was re-diagnosed based on the presence of four putatively derived traits: (1) the large, horizontally-elongate and well-defined blotches in four longitudinal rows of deeper-lying pigmentation on the trunk; (2) the pectoral fin with I+5-6 rays; (3) a separation of the anterior and posterior cranial fontanels by the primordial epiphyseal cartilaginous bar being present only in larger specimens; (4) and the pelvic-fin bases very close to each other, sometimes in contact (Bockmann & Sazima, 2004).More recently, Barbosa & Costa (2010) rejected three of these diagnostic features (characters 1, 2, and 4) from Bockmann & Sazima (2004) due to the presence of pelvic-fin bases very close to each other and of I+5-6 pectoral-fin rays in other species of Trichomycterus not included in the group, as well as due to the impossibility to determine accurately the number of longitudinal rows of blotches that are greatly irregular in their arrangement.As a consequence, Barbosa & Costa (2010) redefined again the T. brasiliensis species-complex based on a single diagnostic feature: the oblique disposition of the opercular odontodes.The four species herein described present some diagnostic characters listed in these hypotheses (e.g., pelvic-fin bases very close to each other and I+5-6 pectoral-fin rays), but the constant changes in the definition of T. brasiliensis species-complex and the unavailable osteological data from all species of Trichomycterus make these hypotheses questionable and to date not consistently demonstrated.
The species of Trichomycterus from laguna dos Patos system are clearly distinguishable from most congeners by the lower number of pectoral-fin rays (modally I+5 in T. brachykechenos and T. poikilos; modally I+6 in T. balios; and I+6 in T. diatropoporos, and T. tropeiro) and by the first pectoral-fin ray not prolonged as a filament.The combination of these two characters is uncommon in valid species of Trichomycterus from southern and southeastern Brazil, being present only in T. davisi, T. mboycy, T. naipi, T. papilliferus, T. perkos, T. plumbeus and T. tropeiro.All these species are restricted to the rio Iguaçu drainage, except for T. davisi that also occurs in the upper rio Paraná and rio Ribeira do Iguape drainages, T. perkos that is distributed in the rio Uruguay and rio Paranapanema drainages, and T. tropeiro which is restricted to the laguna dos Patos system.Two additional undescribed species (see comparative material) from rio Uruguay also possess the combination of these two characters.Costa & Bockmann (1993) suggest that Ituglanis and Scleronema are closely related to TSVSG clade based in two synapomorphies (reduction of the interopercular patch of odontodes and urohyal thin and elongate), and de Pinna (1998) reinforced the monophyly of this clade based on shared three or fewer abdominal vertebrae by its members.However, Datovo & Bockmann (2010) listed a unique derived character shared by at least five genera of the subfamily Trichomycterinae (Bullockia, Hatcheria, Ituglanis, Scleronema and Trichomycterus), the posterior portion of the levator internus 4 originating from the dorsal face of the posttemporo-supracleithrum, and contested the utility of the characters that corroborated the monophyly of the clade Scleronema + Ituglanis + TSVSG (Costa & Bockmann, 1993;de Pinna, 1998).According to Datovo & Bockmann (2010), the reduction of the interopercular patch of odontodes and the thinness and elongation of urohyal lateral processes is present in many other trichomycterines (e.g., Trichomycterus stawiarski and Silvinichthys bortayro Fernández & de Pinna, 2005) and seem to be developed to varying degrees with a continuum of intermediate states between the more extreme conditions.Trichomycterus balios, T. diatropoporos, and T. poikilos present the urohyal with lateral processes with wide bases and decreasing in width distally with rounded tips, but T. brachykechenos possesses the lateral processes of urohyal thin and elongate with pointed tips (Fig. 5), corroborating the statements of Datovo & Bockmann (2010).
Trichomycterus brachykechenos has one of three synapomorphies proposed by Costa & Bockmann (1993) for the genus Ituglanis: the anterior portion of the sphenotic directed anteriorly (Fig. 2d).The other two, autopalatine with a deep concavity on the medial margin and the parietosupraoccipital fontanel (= posterior cranial fontanel) reduced to a small round orifice, are not present in the new species (Fig. 16 and Fig. 2d,respectively).However, the shape of posterior cranial fontanel in T. brachykechenos is intermediary between the typical Ituglanis and the basal trichomycterids, which possess a tiny and wide posterior cranial fontanel, respectively (Fig. 2d, see remarks).Thus, according to the hypothesis of Datovo & Bockmann (2010) and the two characters present in T. brachykechenos -pattern of the posterior cranial fontanel added to anterior portion of the sphenotic directed anteriorly -may indicate a possible relationship with Ituglanis.
Color Pattern.Trichomycterus balios, T. diatropoporos, and T. poikilos shares the two distinct layers of pigmentation in the skin of large specimens as reported for T. castroi by de Pinna (1992b), T. brasiliensis, T. iheringi, T. maracaya, T. mimonha, T. potschi, and undescribed species of the T. brasiliensis complex by Bockmann & Sazima (2004), and T. crassicaudatus, T. diabolus, T. giganteus, T. igobi, T. perkos, T. stawiarski, and T. tropeiro by Datovo et al. (2012).Among the species from laguna dos Patos system, only Trichomycterus brachykechenos lacks the two distinct layers.The distribution of these patterns across Trichomycterus species, however, is mostly unknown because it is missing in most species descriptions or because it is difficult to recognize the two skin layers in specimens preserved for a long period of time (Datovo et al., 2012).
Several species of Trichomycterus have the deeper skin layer (= inner skin layer) usually composed of larger blotches and spots, formed by densely grouped chromatophores (Bockmann & Sazima, 2004).Among the species from laguna dos Patos system, Trichomycterus balios, T. diatropoporos, and T. tropeiro share this pattern of the inner skin layer.Both T. balios and T. tropeiro possess black circular blotches variable in size on the dorsal and lateral surface of body over a lighter background, while T. diatropoporos has black blotches variable in size and shape coalescent dorsally on a lighter background.
The other species from laguna dos Patos system with two distinct layers of pigmentation presents the inner skin layer formed by stripes in some specimens, condition similar to that of T. perkos from the La Plata drainage.
Geographic distribution.The review of a large number of lots of the Trichomycteridae collected in practically all portions of laguna dos Patos system revealed that Trichomycterus is restricted to the northern portion of that basin along the middle and upper stretches of the rio Jacuí and middle and upper stretches of its large tributaries, the rio do Sinos, rio Caí, rio Taquari-Antas, and rio Pardo (Fig. 8).The few lots of Trichomycterus listed in fish collections as having originated in the southern portion of the laguna dos Patos system proved to be Ituglanis, a genus which has an external morphology very similar to Trichomycterus.
The analysis of comparative material from adjacent drainages to the north and northeast of laguna dos Patos system (rio Uruguay, rio Tramandaí, and rio Mampituba basins) allow us to propose that three among the four new species are endemic to the laguna dos Patos system, excepting T. balios, which occurs also in the headwaters of rio Mampituba.However, their degree of endemism is variable.Trichomycterus balios is distributed in the upper courses of rio das Antas, rio Caí, and rio Mampituba basins; T. poikilos is widely distributed in the upper courses of the rio Jacuí basin and tributaries of the rio the Taquari-Antas; T. brachykechenos and T. diatropoporos are known only from few localities in the rio dos Sinos and the rio da Prata basin respectively.Trichomycterus tropeiro is also endemic to the laguna dos Patos drainage and has a very restricted range, occurring only in headwaters of rio das Antas (Ferrer & Malabarba, 2011).Endemism and restricted ranges seem typical among species of Trichomycterus, which is the dominant genus in the compilation of species with restricted-ranges in Nogueira et al. (2010), with 45 species.
The species of Trichomycterus from the laguna dos Patos system usually are distributed in headwaters or upper courses and may demonstrate disjoint distributions in the same basin.Both T. tropeiro and T. balios are found in the rio das Antas, but the first species is known only from localities above 1000 m a.s.l (Ferrer & Malabarba, 2011), while the second occurs in the lower portions between 681 m and 941 m a.s.l.The same distribution pattern is observed in two characid species of the genus Astyanax described from the rio das Antas basin, A. brachypterygium occurring above 1100 m a.s.l. and A. cremnobates restricted to altitudes ranging from 800 to 1000 m a.s.l.(Bertaco & Malabarba, 2001).
Besides both T. balios and T. poikilos occur in the rio Taquari-Antas drainage, they also show disjoint distributions.Trichomycterus balios occurs to the East, in the rio da Prata, a tributary in the right margin of the rio das Antas, and tributaries of the rio das Antas above the mouth of the rio da Prata in both right and left margins.Trichomycterus poikilos occurs to the West in the rio Carreiro, rio Guaporé and rio Forqueta, all right margin tributaries of the rio Taquari-Antas, below the rio da Prata, but is also widely distributed in the upper tributaries of the rio Jacuí basin that are geographically close to the rio Taquari-Antas tributaries (Fig. 8).The occurrence of T. poikilos in close proximity in the upper portions of the tributaries of two sub-drainages (rio Taquari-Antas and upper rio Jacuí) may indicate headwater capture events among these small tributaries.
Trichomycterus diatropoporos is endemic to the rio da Prata basin and occurs sympatrically with Hisonotus prata and an undescribed species of Eurycheilichthys, also endemic to the upper course of the rio da Prata (Carvalho & Reis, 2011).The mountain relief on which the Taquari drainage flows was considered responsible for dividing species distribution in that drainage, as exemplified by H. prata and the undescribed species of Eurycheilichthys (Carvalho & Reis, 2011), and it seems to be also correlated to the restricted distribution range of T. diatropoporos.
Trichomycterus brachykechenos is apparently endemic to the upper course of the rio do Sinos.One sample tentatively identified as T. poikilos was found in other stretch of the upper basin of the rio dos Sinos, but not syntopic with T. brachykechenos.
This study revealed an astonishing undescribed diversity of Trichomycterus in a relatively small region with four undescribed species, along with one species recently described in 2011.We expect that the revision of other understudied basins in southern Brazil will reveal new and undescribed species of Trichomycterus.

Table 1 .
Morphometric data for holotype and paratypes of Trichomycterus balios.SD = standard deviation; N = number of specimens.

Table 2 .
Morphometric data for holotype and paratypes of Trichomycterus diatropoporos.SD = standard deviation; N = number of specimens.

Table 3 .
in T. balios and 12-13 in T. diatropoporos); 23-25 teeth on plate connected to pharyngobranchial 4(Fig.3c;;color pattern of the dorsal and lateral surfaces of body mottled dark brown over a light yellow background or with three stripes with notched borders (dorsosagittal, midlateral, and ventrolateral) (Figs.13-14 vs. the dorsal and lateral surfaces of body with circular black blotches variable in size in T. balios and T. tropeiro, the lateral surface of body with dark blotches variable in size and shape progressively larger and coalescent dorsally thus forming extensive black pigmented regions with light yellow gaps in T. diatropoporos).Trichomycterus poikilos is further distinguishable from T. diatropoporos by the insertion of the first dorsal-fin basal radial anterior to the neural spine of the 20 th -22 th vertebrae (vs.anterior to the neural spine of the 17 Morphometric data for holotype and paratypes of Trichomycterus poikilos.SD = standard deviation; N = number of specimens. th or 18 th vertebrae).Trichomycterus poikilos is further distinguishable from T. tropeiro by the presence of the pelvic girdle and pelvic fins (Figs.13-14; vs. absence); and the absence of the pores i1 and i3 of the infraorbital sensory canal(Fig.2c;vs. presence).

Table 4 .
Morphometric data for holotype and paratypes of Trichomycterus brachykechenos.SD = standard deviation; N = number of specimens.