Revision of genus Steindachneridion (Siluriformes: Pimelodidae)

After several years collecting in the type-localities and studying representative samples of genus Steindachneridion Eigenmann & Eigenmann, 1919 from Brazilian and foreign museums, a taxonomic revision of the Recent species of the genus is presented, including the description of a new species from the rio Iguaçu, above the great falls. Steindachneridion species are large sized fishes, reaching 1000 mm total length or more, and sharing some anatomical characters that, at least tentatively, support the monophyly of the genus. In addition to the general features found in the Pimelodidae, the species S. amblyurum (Eigenmann & Eigenmann, 1888), S. parahybae (Steindachner, 1877), S. doceanum (Eigenmann & Eigenmann, 1889), S. scriptum (Miranda Ribeiro, 1918), S. punctatum (Miranda Ribeiro, 1918), and S. melanodermatum, new species, share the shape of the vomer tooth plates, six to eight branched rays in the dorsal-fin, and a low number of gill-rakers. All species, except fossil ones, are redescribed and a key for their identification is provided.


Introduction
The Neotropical pimelodid catfish genus Steindachneridion Eigenmann & Eigenmann, 1919 has not been revised for almost a century.The reasons are probably related to the fact that species of the genus are naturally scarce and relatively hard to collect, which resulted in very small samples of Steindachneridion species available in ichthyological collections.This has prevented an adequate assessment of the diversity within the genus, or adequate examination of the relationships of Steindachneridion with other pimelodids, which remains unclear (de Pinna, 1998;Lundberg & Littmann, 2003, Lundberg & Akama, 2005).
Our knowledge of the systematics of the genus Steindachneridion may be summed in only a few major studies since the "South American Nemathognathi" of Eigenmann & Eigenmann (1890), that offered a taxonomic revision of all families, genera and species of the Siluriformes, including a brief review of Steindachneridion.A synthesis of the relatively short taxonomic history of this poorly known pimelodid genus is presented below.The first described species of the genus Platystoma parahybae Steindachner (1877) has as type locality both the rio Paraíba do Sul (at Juiz de Fora) and rio Jequitinhonha, Minas Gerais.Eigenmann & Eigenmann (1888), studying a portion of the type material of Platystoma parahybae, described Steindachneridion amblyurum based solely on the specimens from rio Jequitinhonha and erected the genus Steindachneria, selecting S. amblyurum as type species.The generic name was preoccupied in fishes by Steindachneria Goode & Bean, 1888 and was posteriorly replaced by Steindachneridion by Eigenmann & Eigenmann (1919).
In the following year Eigenmann & Eigenmann (1889) de-scribed S. doceanum from the rio Doce, thereby extending the known distribution of genus Steindachneridion to eastern coastal drainages of Brazil.A complete taxonomic revision of the genus, was presented by Eigenmann & Eigenmann (1890) still under name Steindachneria.These authors redescribed the species S. amblyurum, S. parahybae, and S. doceanum, diagnosed them in a key, and included drawings of the arrangement of tooth plates on the vomer in S. amblyurum and S. parahybae.
The first fossil species S. iheringi, was described by Woodward (1898) from the Tertiary beds of Tremembé, São Paulo in the genus Arius, and later transferred to the genus Steindachneridion by Santos (1973).This fossil was first considered as being of Pleistocene age (Travassos & Santos, 1955), but Lima et al. (1985) argued for an Oligocene age.Miranda Ribeiro (1902) cited S. parahybae for the rio Pomba, a tributary of rio Paraíba do Sul at Rio de Janeiro State.
Miranda Ribeiro (1918) described S. scriptum and its "variety" S. scriptum punctatum, both from the rio Uruguay at Itaqui, Rio Grande do Sul State, Brazil; Britski (1969) designated a lectotype for S. scriptum; the type material of both forms was later studied by Garavello (unpubl.), who considered S. punctatum as a valid species.Van der Stigchel (1947) misidentified specimens of S. parahybae collected in Porto Real, rio Paraíba do Sul, Rio de Janeiro State as S. doceanum.Severi & Cordeiro (1994) in a short catalog of fishes and Garavello et al. (1997) in a book on rio Iguaçu, mentioned the occurrence of an unidentified Steindachneridion species at that river basin.Oliveira & Moraes Junior (1997) presented additional data on S. parahybae, based on material deposited at the MNRJ, providing a diagnosis for the genus Steindachneridion.The most recent contribution on the systematics of genus Steindachneridion was the description of a second fossil species, S. silvasantosi by Figueiredo & Costa-Carvalho (1999).After this only Nakatani et al. (2001) published information about larval development of both S. scriptum from rio Paraná and the new species from the rio Iguaçu, and Zaniboni Filho et al. (2004) provided some information on the biology of S. scriptum from the upper rio Uruguay basin.
The purpose of the present study is to review Steindachneridion and to discuss its distribution, which is restricted to eastern Brazilian coastal drainages, plus the upper Paraná (including rio Iguaçu) and rio Uruguay basin.The revision of Steindachneridion (excluding the fossil ones), herein presented, recognizes six Recent species (including a new one).Extensive field work by the author and other Brazilian ichthyologists over the past years has shown the large-sized (up to 1000 mm SL or even more) Steindachneridion species as always occurring in swift-flowing, clear water rivers, running over large stony beds.

Material and Methods
Sixty-one preserved specimens of Steindachneridion were examined during this study.Type specimens of S. amblyurum, S. parahybae, and S. doceanum are deposited at MCZ, and those of S. scriptum at MNRJ and MZUSP, and S. punctatum at the MNRJ.Institutional abbreviations follow Leviton et al. (1985) with addition of Laboratório de Ictiologia Sistemática do Departamento de Ecologia e Biologia Evolutiva, Universidade Federal de São Carlos (LISDEBE).
Measurements were taken to the nearest millimeter with vernier calipers, with exception of standard length, predorsal distance, trunk length, distance dorsal-adipose and adiposecaudal, which were taken with a metallic meter stick.The following counts were taken: 1) number of dorsal-fin rays; 2) number of pectoral-fin rays; 3) number of anal-fin rays; 4) number of pelvic-fin rays; 5) number of caudal-fin rays; 6) number of branchiostegal rays; 7) number of gill-rakers of the first left side branchial arch.Fin counts were expressed by the common number of branched rays and its variation in parenthesis.The following measurements were taken: 1) standard length: from tip of snout to base of caudal fin (SL); 2) head length: from tip of snout to posterior margin of opercle (HL); 3) snout length: from tip of snout to anterior margin of orbit; 4) predorsal distance: from tip of snout to anterior base of first dorsal ray; 5) pre-anal distance: from tip of snout to base of anal-fin insertion; 6) length of base of adipose fin; 7) caudal peduncle depth: the shortest distance of caudal peduncle; 8) head depth: taken at occipital region; 9) body depth: at dorsal-fin origin; 10) orbital diameter: taken horizontally; 11) interorbital width: taken between eyes; 12) mouth width: width of lower jaw; 13) cleithral width: most large distance between cleithral bones; 14) head width: taken at the larger distance between opercular bones of each side; 15) pelvic width: taken at the pelvic-fin insertions; 16) internasal width: taken between anterior nostrils.Morphometric data of body, head, and fins were transformed into logarithms, a matrix of covariance was computed and a size-free canonical variate analysis (Bookstein et al., 1986;Reis et al., 1990) was carried out using the statistical package SAS-PC (1995) to distinguish some morphological traits of S. scriptum, S. punctatum, and S. melanodermatum.Counts are also utilized in the differential diagnosis of species.Burgess, 1989: 282 (ref); Lundberg et al., 1991: 842;Oliveira & Moraes Junior, 1997: 3 (ref);de Pinna, 1998: 314;Lundberg & Littmann in Reis et al., 2003: 443.Diagnosis.Large sized pimelodid fishes, up to 1000 mm or more; head short and depressed without external exposed ossification and covered by skin; supraoccipital process not reaching the anterior nuchal plate; postcleithral and pelvic girdle short and entirely covered by thick skin.Eye small, dorsally located in the anterior surface of head and with orbital margin free.By these characters and other expressed in the species descriptions, Steindachneridion shares a basal position with other genera of group A of the Pimelodidae as proposed by Lundberg et al. (1991).According to the hypothesis raised by the aforementioned authors, the relationships of Steindachneridion lies in a polytomy with other pimelodid genera, among them, Sorubimichthys, Pseudoplatystoma, Hemisorubim, Brachyplatystoma, Sorubim and Platynematichthys.On the other hand, Figueiredo & Costa-Carvalho (1999) discuss some cranial characters of the fossil species S. silvassantosi and suggest that it shares features with, and may be related to, the genera Leiarius, Phractocephalus, and Lophiosilurus.A more basal position for the genus Steindachneridion is suggested by Lundberg & Akama (2005) and some information about a forthcoming contribution presenting some molecular evidence that this genus may be included in the Phractocephalus group is available.Unfortunately the phylogenetic relationships of genus Steindachneridion within the family Pimelodidae are not resolved, remaining only partially known.The characters studied herein may furnish new data for comparisons and discussions, and justify the taxonomic revision of genus Steindachneridion Eigenmann & Eigenmann, 1919.In fact, this genus is actually included in the catfish family Pimelodidae as delimited by Lundberg & Littman (2003), a monophyletic assemblage of small to large sized fishes, currently including 29 genera and 84 species.
Distribution.Known from Southeastern Brazilian drainages of Jequitinhonha, Doce, Paraíba do Sul, upper Paraná and Uruguay rivers, Brazil (Fig. 1).Opercular opening large and branchial membranes joining at narrow isthmus; eight branchiostegal rays; 16-18 gill-rakers on first branchial arch.Lower region of head with arrow-like, shallow gular fold; deep grooves at lower jaw posterior margin.Mouth large and terminal; mouth width 48 to 51.1% of HL; lower jaw shorter than upper jaw; lips thin; posterior postcleithral process short, reaching vertical line passing near posterior margin of supraoccipital process; all barbels narrow and compressed; maxillary barbel very short, reaching or only slightly surpassing anterior insertion of dorsal fin when adpressed; pair of short mental and post-mental barbels on each side.Tooth plates of premaxilla and dentary with villiform teeth; premaxillary tooth plates large; abruptly narrowing and curved inward distally; single vomerine tooth plate grooved medially in adults and juveniles, circumscribed by premaxillary tooth plate; dentary plate large and distally sharp.

Key to the species of
Body profile slight convex between posterior head and dorsal-fin origin; dorsal-fin base slanted; base of adipose fin almost straight; dorsal profile of caudal peduncle deeply concave from end of adipose fin to caudal-fin origin.Predorsal length moderately long, 36.4 to 39.7% of SL.Ventral profile of body almost straight and slightly slanted from tip of snout to end of opercular bone; slightly convex at middle abdominal region, straight at pelvic-fin insertion; base of anal fin slanted; lower caudal peduncle profile slightly concave; cross sec-tion of caudal peduncle at vertical through posterior tip of anal fin approximately oval.Dorsal-fin rays i,7 (6 or 8) first two more or less spinous; dorsal-fin base inserted in dorsal space between vertical through pectoral-fin terminus and analfin origin; dorsal-fin locking mechanism present.Pectoral fin short, fin tip not reaching vertical through middle dorsal-fin insertion; rays i,9 (10), posterior margin truncate; first pectoral-fin ray short and not pungent, both margins devoid of serrae.Pelvic fin short; i,5 rays, fin never reaching anus; tip of unbranched pelvic-fin ray smooth; distal margin of fin truncate; pelvic fin distant from anal-fin origin and inserted at vertical through dorsal-fin insertion, its tip not reaching anus or vertical passing through adipose-fin origin.Anal-fin rays short, i,8 (9,10), distal margin truncate; preanal distance 68 to 72.5% of SL.Caudal peduncle high, its depth 8.7 to 9.3% of SL.Caudal fin notched, dorsal lobe slightly longer than ventral lobe; principal caudal-fin rays, i,15,i.
Body and head, except orbital region covered with thick skin.Ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process short and covered by thin skin anterior to first unbranched dorsal-fin ray, as in S. doceanum and S. amblyurum.Postcleithral process short and entirely covered by skin.
Color in alcohol.Ground color of head, dorsum, and lateral regions of body light gray, ventral region whitish; dorsal and lateral portions of head and trunk with large irregularly distributed dark brown lines, forming bold vermiculated color pattern of dark brown and light gray lines.Eye dark.Dorsal, pectoral, pelvic, anal, and adipose fins uniformly light gray with dark brown lines on rays and membranes; adipose fin with several dark brown lines; caudal fin with dark lines on base of each lobe, gray distally.
Distribution.Known from the rio Paraíba do Sul basin, eastern Brazil (Fig. 1).HL; lower jaw shorter than upper and with thin lips; posterior postcleithral process short, reaching vertical line through posterior supraoccipital process.All maxillary barbels, narrow and depressed; maxillary barbel very long, reaching or only slightly surpassing insertion of adipose fin when adpressed; pair of short mental and post-mental barbels on each side.Tooth plates of premaxillary and dentary with villiform teeth; premaxillary tooth plate slender, medially grooved; sharply curved distally; vomerine tooth plate in adults and juveniles, divided in two small elliptical plates at median region; both circumscribed by premaxillary tooth plate; a single and elongated dentary tooth plate, distally sharp.

Material examined
Body profile slight convex between head and adipose-fin origin; dorsal-fin base slanted; base of adipose fin almost straight; dorsal profile of caudal peduncle deep concave from end of adipose fin base to caudal-fin origin.Predorsal length short, 35.6 to 38% of SL.Ventral profile of body almost straight and slightly inclined from tip of snout to end of opercular bone, slightly convex or almost straight at middle inferior head and abdominal region, almost flat on pelvic-fin insertion; base of anal-fin slanted; lower caudal peduncle profile slightly concave; cross section of caudal peduncle at vertical through posterior tip of anal-fin approximately oval.Dorsal-fin rays i,7(6); dorsal-fin base inserted in the dorsal space between the vertical through the pectoral-fin terminus and the anal-fin origin; dorsal-fin locking mechanism present.Pectoral-fin long and not pungent, reaching the vertical line through middle dorsal-fin base; rays i,9(10); first pectoral-fin ray short and not pungent, both margins devoid of serrae.Pelvic fin long, i,5; inserted at vertical at end of dorsal-fin, concealing the anus and reaching the anal-fin insertion; tip of unbranched pelvic-fin ray smooth; distal margin slightly rounded.Analfin rays elongated i,8(9), distal margin rounded; preanal distance 68.1 to 71.6% of SL; first anal-fin ray smooth, not pungent; its distal margin rounded.Adipose fin very large, leaving a narrow space between dorsal and adipose fin; base of adipose fin almost straight.Caudal peduncle low, its depth 9.2 to 10.2% of SL.Caudal fin distally rounded, upper and lower lobes equal; principal caudal-fin rays, i,15,i.
Body and head, except orbital region, covered with thick layer of skin; scapular bridge and pelvic girdle also entirely covered by skin.Supraoccipital process and anterior nuchal plate covered by thin skin and almost in contact.Posterior postcleithral process short and entirely covered by thick skin.
Color in alcohol.Ground color of dorsal and lateral regions of body light brown; ventral region yellowish; dorsal and lateral portions of head, snout, and trunk with irregularly distributed dark brown large lines, sometimes with large black dots on dorsum; lower region of head and abdomen yellow.Eyes dark.Dorsal, pectoral, pelvic, anal and adipose fins uniformly light gray with black lines or black dots on rays and membranes; several dark brown lines and dots on adipose fin; caudal fin with dark lines and small dots on base, but distally gray.
Distribution.Known from the rio Jequitinhonha basin, Brazil (Fig. 1).Opercular opening large and strongly curved; branchial membranes joining before forming a narrow isthmus; eight branchiostegal rays progressively reduced in size; 18-20 gillrakers on first branchial arch.Lower region of head with an arrow like and shallow gular fold; deep grooves at posterior margin of lower jaw.Mouth terminal; mouth width 49.1 to 52.0% of HL; lower jaw shorter than upper jaw; lips thick; posterior postcleithral process short, reaching vertical line passing through terminus of supraoccipital process.All barbels, narrow and depressed; maxillary barbel short, reaching or only slightly surpassing the median region of pectoral fin when adpressed; a pair of short mental and post-mental barbels on each side.Tooth plates of premaxillary and dentary ramus with villiform teeth; premaxillary tooth plate slender, with median groove and abruptly narrowing and curved inward distally; single vomerine tooth plate grooved medially in adults; vomerine tooth plate divided into two small elliptical plates almost in contact at median region of vomer in juveniles; both vomerine tooth plates circumscribed by premaxillary tooth plate; and single elongate and distally sharp dentary tooth plate.
Body profile slight convex between posterior nuchal plate and origin of adipose fin; dorsal-fin base slanted; region between dorsal and adipose-fin origin slightly concave; dorsal profile of caudal peduncle deeply concave from end of adipose fin to origin of caudal-fin.Predorsal length long, 38 to 40% of SL.Ventral profile of body almost straight and slanted from tip of snout to end of opercular bone, slightly convex at middle inferior head and abdominal region, flat on pelvic-fin insertion; base of anal fin straight and posteriorly slanted; preanal distance 69.3 to 71.6% of SL; lower caudal peduncle profile slightly concave; adipose fin large and convex.Caudal peduncle at vertical through posterior tip of anal fin approximately rounded in crossed section.Dorsal-fin rays i,7(6); dorsal-fin base inserted in dorsal space between vertical through pectoral-fin terminus and anal-fin origin; dorsal fin locking mechanism present.Pectoral fin long, tip of fin surpassing vertical through dorsal-fin insertion; rays i,9(10); distal margin rounded; pectoral spine short and not pungent, both margins devoid of serrae.Pelvic-fin long, its tip not pungent and reaching anal-fin insertion; pelvic-fin rays i,5; its distal margin slightly rounded; pelvic-fin when adpressed concealing anus and reaching anal-fin origin.Anal-fin rays i,8(9), its distal margin rounded.Caudal peduncle low, its depth 7.7 to 9% of SL.Caudal fin slightly notched, with dorsal lobe slightly larger than ventral, fin tip slightly pointed; principal caudal-fin rays, i,15,i.
Body and head except orbital region covered with thick skin.Ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process short and covered by thin skin, very near the anterior nuchal plate.Posterior postcleithral process short and entirely covered by skin.
Color in alcohol.Ground color of head, dorsum and lateral region of body light gray and ventral region yellowish; dorsal and lateral portions of head and trunk with maze dark brown lines forming like a marbled color pattern, combined  with light gray ground color extending onto all fins; lower region of head and abdomen yellowish.Eyes dark.Dorsal, pectoral, pelvic, anal and adipose fins uniformly light gray and with lines forming marbled pattern on rays and membranes; adipose fin with several dark brown lines; caudal fin with dark lines on base of each lobe, gray distally.Opercular opening large and strongly curved forward; branchial membranes joining at narrow isthmus; eight branchiostegal rays reduced in size; 15 to 17 gill rakers on first branchial arch.Lower region of head with an arrow-like, shallow gular fold; deep grooves on each side of lower jaw.Mouth large and terminal; lower jaw slightly shorter than upper jaw; mouth width 38.7 to 47.2% of HL; posterior postcleithral process short, reaching vertical line passing through beginning supraoccipital process; lips thin; all bar-Fig.7. Lateral and dorsal views of S. scriptum.MZUSP 88015, 690 mm SL, Jaguara, rio Grande, cachoeira Mata-Doutor, downstream of Jaguara hydroelectric power dam, São Paulo, Brazil.bels narrow and depressed; maxillary barbel long, when adpressed, reaching vertical line passing through dorsal-fin insertion.Tooth plates of premaxillary and dentary with villiform teeth; each premaxillary and dentary bone has its own tooth patch; premaxillary tooth plates large, unite and with a median groove; abruptly narrowing and curved inward distally; single vomer tooth plate continuous, almost elliptical and circumscribed by the premaxillary tooth plate; single dentary thin tooth plate distally sharp.

Distribution
Body profile deep convex between nuchal plate and caudal peduncle; base of dorsal-fin and anterior region of adipose fin straight; anterior region and insertion of adipose fin slanted; dorsal profile of caudal peduncle slightly concave from adipose fin to base of caudal-fin.Predorsal length 39.4 to 44.1% of SL.Ventral profile of body slanted from tip of snout to abdominal region, almost straight on pelvic and analfin insertions; lower caudal peduncle profile slightly concave.Preanal distance 70 to 75.7% of SL.Caudal peduncle at vertical through posterior tip of anal fin nearly rounded in crosssection.Dorsal-fin rays i,7(6); first two rays not pungent; dorsal fin base inserted in the dorsal space between the vertical through pectoral-fin terminus and vertical line through anal-fin origin; dorsal-fin locking mechanism present.Pectoral-fin rays i,9(10), first pectoral-fin ray not pungent and devoid of serrae; distal margin of fin straight; pectoral-fin short, when adpressed reaching vertical through base of first dorsal-fin ray.Pelvic-fin rays i,5; tip of unbranched pelvic-fin ray smooth and not pungent; slightly rounded distally; tip of pelvic-fin when adpressed surpass the anus, but not reach the anal-fin origin.Anal-fin rays i,8(9,10), pelvic-fin distal margin truncate.Caudal-fin deep notched; dorsal lobe larger than the ventral lobe and both tips slightly rounded; principal caudal-fin rays, i,15(14-16),i; caudal peduncle low, its depth 9.9 to 11.7% of SL.
Body and head except orbital region covered with thick skin; ventral surfaces of pectoral and pelvic girdle entirely covered by skin.Supraoccipital process short covered by thin skin and reaching the vertical through opercular opening; posterior postcleithral process short and entirely covered by skin.
Color in alcohol.Dorsal and lateral regions of body and head light gray and ventral region whitish; dorsal regions of head and trunk with small elongated or striated dark brown marks larger than one orbital diameter, irregularly scattered; juveniles with lateral small dark brown elongated marks and dots on dorsal surface of body.Eyes dark.Dorsal, pectoral, pelvic, anal and adipose fins uniformly dark gray with small black or dark brown elongated marks or large dots scattered on rays and membranes; adipose fin with several dark marks; caudal fin with dark dots on base of each lobe; dark gray distally.
Distribution.Known from upper rio Paraná, and rio Uruguay basins, Brazil (Fig. 1).Opercular opening large and with branchial membranes joining at narrow isthmus; eight branchiostegal rays reduced in size; 12 to14 gill rakers on first branchial arch.Lower region of head with arrow-like, shallow gular fold; deep grooves at lower jaw distal margin.Mouth large and terminal; mouth width 43.4 to 48.0% of HL; lower jaw shorter than upper jaw; thin lips; posterior postcleithral process short, reaching vertical line through distal supraoccipital process; all barbels narrow and depressed; maxillary barbel short, when adpressed reaching or only slightly surpassing the opercular opening; a pair of short mental and post-mental barbels on each side.Tooth plates of premaxillary and dentary provided with villiform teeth; premaxillary tooth plates large, united and grooved at middle, narrowing and curved inward distally; single vomer dental plate not grooved, almost elliptical in adults and juveniles, circumscribed by the premaxillary tooth plate; dentary tooth plate thin, single and distally sharp.
Body profile slightly convex from distal head to dorsal-fin origin; dorsal-fin base and posterior region almost straight; base of adipose fin slanted; dorsal profile of caudal peduncle slightly concave from end of adipose fin to caudal-fin origin.Predorsal length 41.3 to 44.1% of SL.Ventral profile of body straight inclined from tip of snout to end of opercular bone, slightly convex at middle abdominal region, slanted on pelvic and almost straight at anal-fin insertion; lower caudal peduncle profile slightly concave; cross section of caudal peduncle at vertical through posterior tip of anal fin approximately rounded.Dorsal-fin rays i,7(6); first two rays moderately spinous; dorsal-fin base inserted in the dorsal space between vertical through pectoral-fin terminus and anal-fin origin; dorsal fin locking mechanism present.Pectoral fin short and pectoral spine not pungent; fin tip reaching vertical through first dorsal-fin ray; pectoral-fin rays i,9(10), distal margin straight inclined and both margins of unbranched pectoral ray devoid of serrae.Pelvic-fin short; i,5 rays; tip of unbranched pelvic-fin ray not pungent; when adpressed surpassing the anus, but not reaching the anal-fin origin; posterior margin of pelvic-fin slightly rounded; Anal-fin rays i,8(9,10), posterior margin semicircular.Preanal distance 69.5 to 74.6% of SL.Caudal peduncle low its depth 9.8 to 11.1% of SL.Caudal fin slightly notched, with both lobes same sized, fin tip roughly rounded; principal caudal-fin rays, i,15,i.
Body and head, except orbital region covered with thick skin; ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process covered by thin skin, reaching vertical through distal opercular opening.Posterior postcleithral process short and entirely covered by skin.
Color in alcohol.Ground color of head, dorsum and lateral regions of body light gray and ventral region whitish; dorsal and lateral portions of head and trunk with small black and or dark brown circular or semicircular blotches; blotches shorter than one orbital diameter, irregularly scattered; lower region of head and abdomen yellowish; juveniles with lateral small dark brown dots on dorsal surface of body.Eyes dark.Dorsal, pectoral, pelvic, anal and adipose fins uniformly dark gray, small dark brown dotted on rays and membranes; adipose fin with several black or dark brown dots; caudal fin with dark spots on base of each lobe, but distally uniformly dark gray.
Distribution.Known from the upper rio Paraná, and rio Uruguay basin, Brazil (Fig. 1).

Steindachneridion melanodermatum, new species
Fig. 9 Steindachneridion sp.: Severi & Cordeiro, 1994: 73 (ref.);Garavello et al., 1997: 71 (ref.)Diagnosis.Steindachneridion melanodermatum differs from the remaining species of the genus by the following combination of characters: supraoccipital process remote from the anterior nuchal plate by a distance nearly twice the orbital diameter; premaxillary tooth plate slender, separated one from another by a medial groove and curved in distal region; a single oval vomer tooth plate, continuous and circumscribed by the premaxillary plates; 16 to 18 gill rakers on first branchial arch.Lips well developed; maxillary barbel short, reaching to base of unbranched pectoral-fin ray; pelvic fin short, when adpressed only slightly surpassing the anus, but distant from the anal-fin origin; caudal fin slightly notched, dorsal lobe slightly larger than ventral, each lobe nearly rounded distally.Ground color of head and trunk in alcohol dusk brown; abdomen whitish; tiny circular black or dark brown blotches irregularly scattered on the ground color of head and trunk, masking a black dotted pigmentation; caudal peduncle high, its depth 29.5 to 33.4% of HL; head depth nearly equal head width, 74.4 to 97.3%, and head width moderately small, 20.4 to 22.6% of SL.Eyes dorsally placed and in midway between tip of snout and the opercular opening; orbit moderately small, 25.1 to 29.7% of interorbital distance and 8.6 to 9.5% of HL.Opercular opening large; branchial membranes joining at narrow isthmus; eight branchiostegal rays progressively reduced in size; 16-18 gill rakers on first branchial arch.Lower region of head with arrow-like, shallow gular fold; deep grooves at lower jaw distal margin.Mouth large, terminal and with thick lips; mouth width 42.2 to 47.5% in HL; lower jaw shorter than upper jaw; posterior postcleithral process short, reaching vertical through terminus of supraoccipital process; all barbels narrow and depressed; maxillary barbel long, reaching or surpassing median length of dorsal fin when adpressed; pair of short mental and post mental barbels on each side.Tooth plates of premaxillary and dentary with villiform teeth; premaxillary tooth plates slender, with a median groove, narrowing and curved inward distally; single vomer tooth plate continuous, almost elliptical and circumscribed by the premaxillary plate on each side; a single and elongated dentary tooth plate distally sharp.

Description. Morphometric data presented in
Body profile almost straight from the nuchal plate to dorsal-fin; dorsal-fin base slanted and profile between dorsal-fin and adipose-fin insertion slightly concave; base of adipose fin slanted; dorsal profile of caudal peduncle deep concave between adipose and caudal fin.Predorsal length 41.4 to 44.3% of SL.Ventral profile of body slanted from tip of snout to end of opercular bone; convex in abdominal region and nearly flat on pelvic and anal-fin insertions; lower caudal peduncle profile slightly concave.Caudal peduncle at vertical passing through posterior tip of anal fin approximately rounded in cross-section.Dorsal-fin rays i,7(6); the first two slightly spinous; dorsal-fin base inserted in the dorsal space at a vertical after pectoral-fin and through anal-fin origin; dorsalfin locking mechanism present.Pectoral-fin short; first pectoral ray not pungent; both margins devoid of serrae; pectoralfin length when adpressed, reaching before the vertical through dorsal-fin origin; i,9(10) rays; posterior margin truncate.Pelvic-fin rays i,5; tip of unbranched pelvic ray short and smooth; when adpressed only slightly surpassing the anus; distant from anal-fin origin.Distal margin of pelvic-fin roughly rounded.Anal-fin rays i,8 (9), posterior margin truncate; preanal distance 72.6 to 75.5% of SL.Caudal peduncle low, its depth 9 to 9.6% of SL.Caudal fin slightly notched, dorsal lobe slightly larger than ventral, both tip nearly rounded; principal caudal-fin rays, i,15(14),i.
Body and head, except orbital region covered with thick skin; ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process short covered by thin skin, reaching vertical through posterior opercular opening.Posterior postcleithral process short and entirely covered by skin.
Color in alcohol.Ground color of head and dorsal regions of body black or dark brown; ventral region whitish; dorsal and lateral regions of head and dorsum with minute dark brown circular blotches or dots shorter than one orbital diameter, irregularly scattered on background; lower region of head and abdomen progressively whitish.Eyes dark.Dorsal, pectoral, pelvic, anal and adipose fins uniformly black or dark brown combined with small black or dark brown dots scattered on rays and membranes; adipose fin with several minute black or dark brown dots; caudal fin dark dotted on base of each lobe; distal regions uniformly dark.
Etymology.Melanodermatum after the Greek melanos = black and dermatus = skin, referring to the full dark brown ground color of body, a color pattern unique in the genus.
Distribution.Known from the rio Iguaçu at upper Paraná Basin, border of Paraná and Santa Catarina States, Brazil (Fig. 1).

Notes on the rio Iguaçu and localities of S. melanodermatum.
The rio Iguaçu extends almost 1,080 km, descending approximately 830 meters from its headwaters to its mouth just a little below the Iguaçu falls at the border between Brazil, Argentina, and Paraguay.Its headwaters are situated on the eastern Serra do Mar area, which is included in the First Paranaense Plateau, near the city of Curitiba.Upriver, between the localities of Engenheiro Blay and Porto Amazonas, the rio Iguaçu includes several and extensive clear water regions, running over stony beds.As mentioned by Maack (1968) this area of rio Iguaçu drainage has very old rocky beds previous to the Devonian Period constituting the Second Paranaense Plateau.Between the localities of Porto Amazonas and União da Vitória, the river includes very old beds but also several meandrous and extensive flooded areas.Below this area, it crosses the Boa Esperança mountains and reaches the Third Paranaense Plateau, were the rocky beds are younger, including rapids and some falls towards the large Iguaçu falls before meeting the rio Paraná.The collecting localities of S. melanodermatum are situated at the Third Paranaense Plateau, after the Boa Esperança mountains; in these places the river has many large falls, variable depths, but it always has a very swift water flow, running over large rocky beds.Both left and right banks have native vegetation formations of open fields (campos limpos) with sparse woodlots (capões), generally concentrated near the riparian forest, in the banks of the main channel of the river and at its main tributaries.Presently, the portion of the rio Iguaçu running over the Third Paranaense Plateau is deeply modified by the dams of several hydroelectric power plants, and S. melanodermatum may be found only between these dams, inhabiting stretches of the river where the natural flow of water is still preserved.

Discussion
Among the characters of external morphology mentioned by Eigenmann & Eigenmann (1890) to establish the genus Steindachneridion, one of the most relevant is the arrangement of the villiform tooth plates.Those are disposed in an anterior premaxillary large tooth plate and each premaxilla has its own independent plate; these meet and are fused at the symphysis on the midline; a pair of tooth plates on the vomer in S. amblyurum and juveniles of S. doceanum, but only one elongated posterior vomerine plate in S. parahybae, S. scriptum, S. punctatum and S. melanodermatum.S. doceanum possess a vomer tooth plate in an intermediate condition between S. amblyurum and the single plate showed by S. parahybae, S. scriptum, S. puctatum and S. melanodermatum.The paired vomerine plates in S. doceanum remain contiguous on juvenile and in contact on adult specimens seeming to coalesce during their ontogeny.The arrangement of vomerine tooth plates in Steindachneridion was considered by Eigenmann & Eigenmann (1890) to be similar to the condition found in Duopalatinus Eigenmann & Eigenmann, 1888. Britski (1981) when describing genus Merodontotus also identified the double vomer tooth plates of this genus, but considered Merodontotus different from Steindachneridion based on shape of the premaxillary tooth plates and general body shape.In spite of the similar morphology of the vomer tooth plates in Duopalatinus, Merodontotus and Steindachneridion, Lundberg et al. (1991), de Pinna (1998) and Lundberg & Akama (2005) did not confirm any hypothesis of a possible close relationship between these genera, and considered each genus as belonging to distinct groups within the Pimelodidae.Lundberg et al. (1991) considered Duopalatinus included within their Callophysus-Pimelodus clade while Merodontotus and Steindachneridion were considered different genera within their Group A. Lundberg & Akama (2005) also suggested a more basal position for this genus in the Pimelodidae relationships.
Concerning the morphology of head, S. amblyurum presents the supraoccipital process almost in contact with the anterior nuchal plate, in a similar way as S. doceanum and S. parahybae.It differs from S. scriptum, S. punctatum, and S. melanodermatum where a distance of one or two orbital diameters is always present.Concerning to body form and size of fins, S. amblyurum differs from the remaining species of this genus by having an elongated body, combined with a narrow head and pectoral girdle.This species has elongated dorsal, pectoral, pelvic, adipose and anal fins and a pair of long maxillary barbels reaching the beginning of adipose fin, distinct from the general pattern observed in the remaining Steindachneridion species.Steindachneridion amblyurum also differs from its congeners by having a distally rounded caudal fin, contrasting with S. doceanum, S. parahybae, S. scriptum, S. punctatum, and S. melanodermatum where it is notched.The fin lengths also distinguish S. parahybae from S. doceanum, where the elongated pectoral, pelvic and anal fins, combined with the position of anal opening offer different conditions: while in S. doceanum the anal opening is positioned between the pelvic fins, in S. parahybae, it is positioned far distant from the pelvic fins insertion.Possessing short pectoral and pelvic fins, S. parahybae also differ from the remaining species of the genus.
Besides the dark-colored S. melanodermatum, all Steindachneridion species share a similar color pattern, with light grayish or brownish ground color pattern combined with dark brown, vermiculated dark stripes.Dots are also present in S. amblyurum, S. doceanum and S. parahybae and narrow dark brown lines or small dots in, respectively, S. scriptum and S. punctatum.
The new species S. melanodermatum, can be also distinguished from congeners of Paraná-Uruguay basins by several morphometric traits as can be seen in Table 3 and Fig. 10.A size-free canonical variate analysis of combined samples of S. scriptum, S. punctatum and S. melanodermatum reveals that the two first canonical variates account 94.7% of the variation.In the graph of individual scores (Fig. 10) for the three Steindachneridion species, the first canonical variate (CV 1) discriminates S. scriptum from S. punctatum and S. melanodermatum while CV 2 discriminates S. melanodermatum from the other two species.The highest canonical coefficients (Table 3) for the caudal peduncle depth (-0.7381), preanal distance (0.6205), and orbital diameter (-0.5114) indicate these characters as being the best to discriminate S. melanodermatum from the other species along the CV 1.In the CV 2 the greatest head length (0.4959) and scapular bridge width (0.3967) also discriminates S. scriptum from S. punctatum.
Distribution.This peculiar distribution of Steindachneridion species is perhaps due to several Tertiary geological events causing isolation in mostly of the east coastal rivers of Brazil (Ab´Saber, 1957), combined with some Quaternary events established the actual scenario for the distribution of this genus.The species S. scriptum and S. punctatum are restricted to the upper rio Paraná and rio Uruguay basins.The upper rio Paraná basin was considered by Vari (1992) as an endemic region for three species of the family Curimatidae: Cyphocharax vanderi Britski, C. modestus (Fernandez-Yepez) and C. nagelii (Steindachner).The portion of Paraná river basin is here considered to be an area drained by this river above the now drowned Sete Quedas falls.Castro & Casatti (1997) and Bockmann & Sazima (2004) also assumed this as an endemic area for the southeastern Brazilian ichthyofauna.According to Britski & Langeani (1988) for species of genus Pimelodus Lacépède, 1803 became isolated from the São Francisco and Tocantins drainages in early Tertiary.The same phenomenon can be verified for the rio Uruguay that became isolated from rio Paraná only in Miocene period, when the upper rio Uruguay section became isolated from the upper Paraná (Beurlen, 1970).At that time, the rio Uruguay changed its course and joined to the lower rio Paraná, after remaining a great part of this period in contact with the upper rio Paraná basin.That may perhaps explain the distribution of both S. scriptum and S. punctatum in the upper rio Paraná and Uruguay basins.
Recent palynologic studies done by Lima et al. (1985) from Cenozoic sediments from the Taubaté basin attribute an Oligocene age for the ichthyological fossils from the Tremembé beds, at the rio Paraíba do Sul basin.The fossil Steindachneridion iheringii (Woodward), first considered as a Pleistocene species from the Tremembé Formation in front of the Oligocene age dated by Lima et al. (1985) must be considered as modern fishes.This new age for this fossil species is important for the discussion on the different endemism showed by genus Steindachneridion.Considering the species S. parahybae, S. doceanum, S. amblyurum, and the upper rio Paraná species S. scriptum, S. punctatum, and S. melanodermatum might have become isolated in their respective river basins by that time.Haseman (1911) discussed the isolation caused by Iguaçu falls in most of rio Iguaçu basin, a fact reinforced by Garavello (1977) and Garavello et al. (1997) despite of the recent age of lower section of this river, including the Iguaçu falls.According with Bigarella & Salumuni (1957), by tectonic reactivation in the Pleistocene period, three sections of rio Iguaçu have broken up the river flow, forming large lakes in isolated compartments.This phenomenon caused isolation of different segments of the whole Iguaçu basin, with predictable consequences on the ichthyofauna.Several Characiformes species, e.g.Psalidodon gymnodontus, Astyanax gymnogenys, Hasemania maxillaris, Hasemania melanura, Apareiodon vittatus and Oligosarcus longirostris, several Siluriformes, such as Pimelodus ortmanni, Rhamdia branneri, Glanidium ribeiroi, Heptapterus stewarti, Rhamdiopsis moreirai, Pariolius hollandi, Hypostomus derbyi, Trichomycterus castroi and the Trichomycterus species described by Wosiacki & Garavello (2004), revealed the high level of endemism of this isolated drainage.Steindachneridion melanodermatum further corroborates this fact for the rio Iguaçu ichthyofauna.
The distribution of the remaining three species of the genus, S. parahybae, S. doceanum, and S. amblyurum, following Pflug (1969), may reflect the Quaternary isolation of the Brazilian eastern coast.Steindachneridion doceanum is primarily found in the main channel of rio Doce that have become isolated from the rio Doce valley only during the Quaternary; this fact was also mentioned by Menezes (1987) when studying isolated species of genus Oligosarcus from the eastern coast of Brazil.Due to this factor, S. doceanum might perhaps have become secondarily isolated from S. amblyurum which is endemic from rio Jequitinhonha and from S. parahybae, which is endemic to the rio Paraíba do Sul basin.

Comparisons.
Steindachneridion is distinguished from other genera of the Pimelodidae by a combination of features whose phylogenetic relationships are not yet fully determined.Combined characteristics shown to be useful for comparisons and for the identification of an affinity species group whose features, some of them derived, support the genus.The combination of: (1) supraoccipital process short (reduced) and externally not meeting the anterior nuchal plate; (2) tooth plates of premaxilla and dentary with villiform teeth, premaxilla and dentary with patch grooved at medial region and vomer with one or two isolated tooth plates; (3) head relatively small, covered by thick skin; (4) eyes relatively small, with orbital margin free; (5) eight branchiostegal rays; (6) seven dorsalfin rays; (7) low dorsal fin with short dorsal fin spine, not pungent; (8) pectoral fin spine short, not pungent and with both margins devoid of serrae; (9) 12 to 17 gill-rakers on first branchial arch; (10) relative long and straight-margined adipose fin; and caudal fin notched, except in S. amblyurum, furnish the differential diagnosis for the genus.

Fig. 10 .
Fig. 10.Projection scores of individuals of three species of Steindachneridion from Paraná and Uruguay basins on the first two canonical variates, CV1 and CV2.
Description.Morphometric data presented in Table1; maximum body length 420 mm SL.Snout slender; snout tip almost elliptical in dorsal view; snout length 12.9 to 13.1% of SL; anterior pair of nostrils inserted more widely spaced apart than posterior pair; each pair of nostrils protruding on dorsal snout profile.Head long in dorsal view and depressed in lateral view; head low its depth 55.8 to 79.6% of head width;
tip of snout nearly rounded in dorsal view and slightly depressed in lateral view; head depth shorter than its width 63.4 to 88.4%; head depth 15.1 to 21.7% of SL; head length 28.4 to 30.8% of SL.Dorsal profile of head almost straight from tip of snout to supraoccipital process; slightly depressed between from this point to anterior nuchal plate; supraoccipital process distant from the nuchal plate by nearly one orbital diameter long.

Table 2 ;
maximum body length 532 mm SL.Snout slender and robust; snout tip roughly elliptical in dorsal view; 12.1 to 13.3 % of SL; each pair of nostrils protruding on dorsal snout profile; anterior pair of nostrils nearly equidistant from each other as in posterior pair.Head long in dorsal view and slightly depressed in lateral view; head depth nearly long as head width, 74.4 to 97.3%; head depth 17.8 to 21.2% of SL; head length 28.3 to 29.5% of SL.Dorsal profile of head almost straight from tip of snout to supraoccipital process, slightly depressed at interorbital space; slight convex between this point and the dorsal-fin origin; distance between supraoccipital process and anterior nuchal plate separated by near two orbital diameter.

Table 3 .
Coefficients of the original variables in the two first canonical axis (CV).