MZUSP 115061, 26.4 mm SL, female, Brazil, Paraná State, boundary between municipalities of Cambira and Apucarana, ribeirão Cambira, affluent of rio Ivaí, upper rio Paraná basin, 23°38'54"S, 51°29'58"W, coll. Zawadzki CH, de Paiva S, 29 October 2007.

All from Brazil, Paraná State. DZSJRP 18244, 3 males, 26.3−26.8 mm SL, ribeirão Salto Grande, rio Ivaí basin, municipality of Maria Helena, 23°37'08"S, 53°12'18"W, coll. Graça WJ, 30 December 2004. LBP 7358, 1 female, 28.4 mm SL, 1 unsexed, 12.4 mm SL, ribeirão Keller, rio Ivaí basin, boundary between municipalities of Marialva and Bom Sucesso, 23°38'30"S, 51°51'33"W, coll. Devidé R, 15 October, 2002. LBP 13332, 1 male, 23.2 mm SL, 1 unsexed c&s, 23.7 mm SL, rio Mourão, rio Ivaí basin, municipality of Campo Mourão, 24°02'23"S, 52°16'22"W, coll. Zawadzki CH, November 2010. LBP 13333, 1 male, 23.6 mm SL, 1 female, 25.4 mm SL, rio Mourão, rio Ivaí basin, municipality of Campo Mourão, 24°02'23"S, 52°16'22"W, coll. Pavanelli CS, 4 December 2006. LBP 13334, 1 male, 24.9 mm SL, ribeirão Keller, rio Ivaí basin, boundary between municipalities of Marialva and Bom Sucesso, 23°38'30"S, 51°51'32"W, coll. Zawadzki CH, November 2010. LBP 13335, 1 male, 26.0 mm SL, ribeirão Salto Grande, rio Ivaí basin, municipality of Maria Helena, 23°37'08"S, 53°12'18"W, coll. Graça WJ, 30 December 2004. LBP 14917, 4 females, 28.8−29.6 mm SL, 2 males, 26.6−27.4 mm SL, ribeirão Cambira, rio Ivaí basin, boundary between municipalities of Cambira and Apucarana, 23°58'54"S, 51°29'58"W, coll. Zawadzki CH, de Paiva S, 29 November 2007. LBP 17578, 3 females, 27.7−30.4 mm SL, 2 males, 25.4−26.1 mm SL, rio Mourão, rio Ivaí basin, boundary between municipalities of Engenheiro Beltrão and Quinta do Sol, 23°49'41"S, 52°11'43"W, coll. Zawadzki CH, Ruiz HB, Vieira RS, 01 April 2013. MCP 47860, 1 male, 25.6 mm SL, 1 female, 25.9 mm SL, ribeirão Salto Grande, rio Ivaí basin, municipality of Maria Helena, 23°37'08"S, 53°12'18"W, coll. Graça WJ, 30 December 2004. NUP 3578, 7 females, 27.8−28.1 mm SL, 8 males, 24.7−26.8 mm SL, 1 female c&s, 27.6 mm SL, 1 male c&s, 25.5 mm SL, ribeirão Salto Grande, rio Ivaí basin, municipality of Maria Helena, 23°37'08"S, 53°12'18"W, coll. Graça WJ, 30 December 2004. NUP 7065, 1 male, 23.3 mm SL, 1 female, 25.4 mm SL, 1 c&s unsexed, 24.5 mm SL, rio Mourão, rio Ivaí basin, municipality of Campo Mourão, 24°02'23"S, 52°16'22"W, coll. Zawadzki CH, 7 April 2009. NUP 9839, 1 male, 25.3 mm SL, 1 female, 25.8 mm SL, 1 female c&s, 25.0 mm SL, collected with holotype. NUP 15614, 10, 3 males, 25.9−26.5 mm SL, 7 females, 27.2−29.9 mm SL, rio Mourão, rio Ivaí basin, municipality of Engenheiro Beltrão, 23°37'41"S, 52°03'38"W, coll. Zawadzki CH, Ruiz HB, Silva HP, 22 October 2012. ZUEC 8006, 2, unsexed, 25.0−27.9 mm SL, rio Mourão, rio Ivaí basin, municipality of Engenheiro Beltrão, 23°37'41"S, 52°03'38"W, coll. Zawadzki CH, Ruiz HB, Silva HP, 22 October 2012. ZMA 250.056, 2, 1 male, 26.1 mm SL, 1 female, 25.6 mm SL, rio Mourão, rio Ivaí basin, municipality of Engenheiro Beltrão, 23°37'41"S, 52°03'38"W, coll. Zawadzki CH, Ruiz HB, Silva HP, 22 October 2012.

Hisonotus oliveirai can be distinguished from all congeners, except Hisonotus insperatus Britski & Garavello, 2003, Hisonotus luteofrenatus and Hisonotus paresi, by having odontodes forming longitudinally aligned rows (one odontode after the other, but not necessarily forming parallel series) on head and trunk, Fig. 2(A), (B) (vs. odontodes not forming longitudinally aligned rows). Additionally, the new species can be distinguished from all congeners except Hisonotus insperatus, Hisonotus luteofrenatus, Hisonotus paresi, and Hisonotus piracanjuba by having a pair of rostral plates at the tip of the snout (vs. a single rostral plate). Moreover, Hisonotus oliveirai can be further distinguished from all congeners except Hisonotus bockmanni, Hisonotus chromodontus, Hisonotus insperatus, Hisonotus luteofrenatus, and Hisonotus paresi by having a functional v-shaped spinelet (vs. spinelet non-functional, square-shaped, or absent). The new species can be distinguished from Hisonotus bockmanni and Hisonotus paresi by lacking contrasting dark geometric spots on the anterodorsal region of the body (vs. presence); from Hisonotus insperatus by having small, inconspicuous odontodes forming rows on the head and trunk (Fig. 2A, B; vs. large, conspicuous odontodes forming rows on the head and the trunk, Fig. 2E, F), a deeper head 51.6−59.2% HL (vs. 44.3−48.7% HL) and higher suborbital depth 20.9−25.5% HL (vs. 16.6−20.1% HL); from Hisonotus luteofrenatus by having a deeper caudal peduncle 10.8−12.5% SL (vs. 8.9−10.2% SL) and shorter snout 46.9−52.2% HL (vs. 67.0−75.3% HL); from Hisonotus paresi by a having deeper head 51.6−59.2% HL (vs. 42.4−47.7% HL), more premaxillary teeth 11−18 (vs. 6−10), and more dentary teeth 11−15 (vs. 4−7); fromHisonotus piracanjuba by having a deeper caudal peduncle 10.8−12.5% SL (vs. 8.3−9.5% SL), and shorter snout 46.9−52.2% HL (vs. 67.7−72.7% HL).

Morphometric data presented in Table 1. Maximum body length 28.4 mm SL. Dorsal profile of head slightly convex to straight from upper part of rostrum to posterior margin of nares, convex from eyes to posterior margin of parieto-supraoccipital, and straight to dorsal-fin origin. Dorsal profile of trunk slightly concave and descending from dorsal-fin origin to end of dorsal-fin base, straight to caudal peduncle. Ventral profile strongly concave from snout tip to opercular region; convex from opercular region to anal-fin origin; concave to caudal-fin insertion. Greatest body depth at dorsal-fin origin (18.6−23.9% SL). Greatest body width at opercular region, gradually decreasing towards snout and caudal fin. Cross-section of caudal peduncle almost ellipsoid; rounded laterally and almost flat dorsally and ventrally.

Head rounded in dorsal view, snout round to slightly pointed. Dorsal and ventral series of odontodes along anterior margin of snout completely covering its tip; odontodes larger than remaining ones on head. Odontodes on head and trunk hypertrophied and arranged in longitudinal rows (most prominent on head). Eyes moderately small (13.9−17.6% in HL), dorsolaterally positioned. Lips roundish with papillae uniformly distributed on base of dentary and premaxilla and slightly decreasing distally. Lower lip larger than upper lip; its border fringed. Maxillary barbel present; joined to lower lip by membrane for half its length. Teeth slender and bicuspid; mesial cusp larger than lateral cusp. Premaxillary teeth 11−18. Dentary teeth 11−15.

Dorsal-fin ii, 7; dorsal-fin spinelet short and V-shaped; dorsal-fin lock functional; dorsal-fin origin slightly posterior to pelvic-fin origin. Tip of adpressed dorsal fin almost reaching end of anal-fin base. Pectoral-fin i, 6; its tip almost reaching middle of pelvic-fin unbranched ray length when depressed. Pectoral axillary slit present between pectoral-fin insertion and lateral process of cleithrum. Pectoral spine supporting odontodes on ventral, anterior and dorsal surfaces. Pelvic-fin i, 5; tip of pelvic-fin longest ray almost reaching anal-fin origin when depressed in females and reaching anal-fin origin in males. Pelvic-fin unbranched ray with dermal flap along its dorsal surface in males. Anal-fin i, 5; its tip reaching 7th or 8th plate from its origin. Caudal-fin i, 14, i; distal margin forked. Adipose-fin absent. Total vertebrae 27.

Body covered with bony plates except above lower lip, around pectoral and pelvic-fin origins and on dorsal-fin base. Cleithrum and coracoid totally exposed. Arrector fossae partially to completely enclosed by ventral lamina of coracoids. Abdomen entirely covered by plates (Fig. 3A); abdomen covered by large, elongate lateral plate series, formed by two lateral rows, approximately of same size; median plates formed by two patterns of plate distributions; first, median plate series not reaching anal shield plates with lateral plate series beginning to contact each other at middle of abdomen; second, median plate series reaching anal shield and lateral plate series remaining separate; anal plates series covered by large square or triangular plates. Body entirely covered laterally by plates (Fig. 3B); mid-dorsal plates poorly developed and reaching middle of dorsal-fin base; median plates series continuous in median portion of body; mid-ventral plates reaching vertical through end of dorsal-fin base.

Parts of dorsal head bone plates presented in Fig. 3C. Snout tip formed by one pair of square rostral plates (r). Nasal (n) rectangular, forming anterior medial nostril margin, posterior nasal margin contacting frontals (f), anterior and lateral margins contacting pre-nasals (pn). Pre-nasals (pn) positioned posterior to rostral plates (r); formed by two large square-shaped plates, one small and triangular and one elongated and rectangular between nares. Posterodorsal head plates consist of compound pterotic (cpt), parieto-supraoccipital (soc) and frontal (f; largest bones of head), prefrontal (pf) and sphenotic (sp). Compound pterotic (cpt) covered with few and small, unclustered fenestra. Lateral surface of head illustrated in Fig. 3D. Posterior rostrum plates pr1-pr2 smallest, rectangular shaped; pr4-pr3 largest, first rectangular and second square. Complete infraorbital plate series (io1-io5), present just above posterior rostrum series, all covered by laterosensory canal system; io2 largest and io5 smallest; io3, io4 and io5 forming inferior orbital margin of eyes. Preopercle (pop) elongate and rectangular, covered by laterosensory canal; preopercle present under pr4, io4 and io5, and upper cp1, cp2 and op. Subocular cheek plates (cp1-cp2) and opercle (op) form posterior lateral margin of head.

Pale yellowish ground color. Dorsal surface of head dark brown, except for pale yellowish areas on snout tip, lateral margin of head and tip of parieto-supraoccipital. Three dark-brown saddles crossing dorsum, reaching longitudinal dark stripe on side of trunk: first below dorsal-fin origin, second typically at adipose-fin region, and third at end of caudal peduncle. Ventral region of anal-fin origin with small single-chromatophore spots. Caudal fin hyaline with two black bars; first at caudal-fin origin, second at middle of caudal fin (Fig. 1).

Adult males are distinguished by having a papilla at the urogenital opening (vs. papilla absent in females); a pelvic fin that extends beyond anal-fin origin (vs. pelvic fin not reaching anal-fin origin in females); and an unbranched pectoral- and pelvic-fin ray supporting a dermal flap on their proximal dorsal surface in males. Both sexes have a membrane at anal opening; however, the membrane is longer and large in females (Fig. 4A) than in males (Fig. 4D), covering almost the entire urogenital opening.

Hisonotus oliveirai is only known from four small to medium-sized streams, the ribeirão Salto Grande, ribeirão Keller, rio Mourão, and the ribeirão Cambira, all tributaries of the rio Ivaí in the upper rio Paraná basin (Fig. 5A).

The specific epithet oliveirai (a noun in the genitive case) is a patronym honoring professor Claudio Oliveira from the Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Botucatu, São Paulo State, in recognition of his dedication and contributions to the studies of Neotropical freshwater fishes.

MZUSP 115062, 26.2 mm SL, female, Brazil, Mato Grosso State, municipality of Santo Afonso, riacho Águas Claras, affluent rio Sepotuba, rio Paraguay basin, 14°21'03"S, 57°33'07"W, coll. Troy WP, 14 September 2010.

All from Brazil, Mato Grosso State, rio Sepotuba basin. DZSJRP 18245, 2 females, 19.9−24.3 mm SL, collected with holotype. LBP 13347, 2 females, 18.9−19.6 mm SL, collected with holotype. LBP 13351, 9, 14.7−24.3 mm SL, riacho Águas Claras, Santo Afonso, 14°21'03"S, 57°33'07"W, coll. Troy WP, April 2012. LBP 13352, 1, 23.7 mm SL, riacho Águas Claras, Santo Afonso, 14°21'03"S, 57°33'07"W, coll. Troy WP, April 2012. LBP 17532, 1 male 22.6 mm SL, 2 female 19.5−23.8 mm SL, 1 unsexed not measured, riacho Maracanã, boundary between municipalities of Santo Afonso and Nova Marilândia, 14°22'40"S, 57°35'11"W, coll. Troy WP, Paliga T, Silva VM, 3 April 2010. NUP 10928, 2 males, 23.2−24.2 mm SL, 2 c&s, 23.6−24.2 mm SL, 1 unsexed not measured, collected with holotype. NUP 10976, 3 unsexed, 16.7−20.5 mm SL, riacho São Jorge, municipality of Santo Afonso, 14°27'26"S, 57°34'34"W, coll. Zawadzki CH, Troy WP, 19 August 2010.

Hisonotus paresi can be distinguished from all congeners, except Hisonotus bockmanni, by the presence of contrasting dark geometric spots on the anterodorsal region of body (vs. absence of geometric spots). Additionally, the new species can be distinguished from all congeners, except Hisonotus insperatus, Hisonotus luteofrenatus, Hisonotus oliveirai, Hisonotus piracanjuba) by having a pair of rostral plates at the tip of the snout (vs. a single rostral plate). Also Hisonotus paresi can be distinguished from all congeners, except Hisonotus insperatus, Hisonotus luteofrenatus and Hisonotus oliveirai by having odontodes forming longitudinally aligned rows on head and trunk, Fig. 2C, D (vs. odontodes not forming longitudinally aligned rows). The new species can be distinguished from Hisonotus bockmanni by having a continuous median series of perforated plate (vs. median plate series of perforated plates discontinuous, that is, with a gap of unperforated plates), by lacking unpaired plates between the contra-lateral dorsal series (vs. having two tiny unpaired plates between the contra-lateral dorsal series, placed eight plates posterior to dorsal fin – see fig. 4 in Carvalho and Datovo 2012), and by having the anterior half of the caudal fin darkly pigmented medially (vs. caudal fin with anterior half hyaline); from Hisonotus insperatus by a longer pectoral-fin spine, 27.0−30.1% in SL (vs. 20.6−25.9%); from Hisonotus luteofrenatus by a longer head 36.1−41.7% SL (vs. 28.8−33.3%), smaller orbital diameter 11.0−14.1% HL (vs. 15.0−18.1%) and shorter snout 50.7−57.1% HL (vs. 67.0−75.3%); from Hisonotus oliveirai by lower head depth 42.4−47.7% HL (vs. 51.6−59.2%), fewer premaxillary teeth 6−10 (vs. 11−18) and fewer dentary teeth 4−7 (vs. 11−15); from Hisonotus piracanjuba by longer head 36.1−41.7% SL (vs. 27.9−32.2), deeper caudal peduncle 10.2−11.3% SL (vs. 8.3−9.5%), fewer premaxillary teeth 6−10 (vs. 14−22) and fewer dentary teeth 4−7 (vs. 12−19).

Morphometric data presented in Table 1. Maximum body length 26.2 mm SL. Lateral profile of head convex; straight from upper part of rostrum to posterior margin of nares, slightly curved from eyes to posterior margin of parieto supraoccipital, almost straight to dorsal-fin origin. Dorsal profile of trunk slightly concave, descending from base of dorsal-fin origin to end of dorsal-fin base, straight to caudal peduncle. Ventral profile slightly concave from snout tip to pectoral-fin origin, convex to anal-fin origin, slightly concave to caudal peduncle. Greatest body depth at dorsal-fin origin (16.9−20.7% SL). Greatest body width at opercular region, gradually decreasing towards snout and caudal fin. Cross-section of caudal peduncle almost ellipsoid; rounded laterally and almost flat dorsally and ventrally.

Head rounded in dorsal view. Snout slightly pointed, its tip rounded, elongated (50.7−57.1% HL) and depressed in front of each nostril on dorsal surface. Dorsal and ventral series of odontodes completely covering anterior margin of snout; odontodes of snout similar in size to remaining ones found on head. Snout tip lacking band devoid of odontodes. Odontodes on head and trunk well defined and arranged into longitudinal rows (character more prominent in head). Eyes small (11−14.1% HL), dorsolaterally positioned. Lips roundish and papillose; uniformly distributed on base of dentary and premaxilla and slightly decreasing distally. Lower lip larger than upper lip; its border strongly fringed. Maxillary barbel present. Teeth slender and bicupid; mesial cusp larger than lateral cusp. Premaxillary teeth 6−10. Dentary teeth 4−7.

Dorsal-fin ii, 7; dorsal-fin spinelet short and V-shaped; dorsal-fin lock functional; its origin slightly anterior to pelvic-fin origin. Tip of adpressed dorsal-fin rays surpassing end of anal-fin base. Pectoral-fin i, 6; tip of longest pectoral-fin ray almost reaching half of pelvic-fin length, when depressed. Pectoral axillary slit present between pectoral-fin insertion and lateral process of cleithrum. Pectoral spine supporting odontodes anteroventrally. Pelvic-fin i, 5; its tip almost reaching anal-fin origin when depressed in females and reaching anal-fin origin in males. Pelvic-fin unbranched ray with dermal flap along its dorsal surface in males. Anal fin i, 5; its tip reaching 7th and 8th from its origin. Caudal-fin i, 14, i; distal margin emarginated. Adipose-fin absent. Total vertebrae 27.

Body covered with bony plates except on ventral part of head, around pectoral and pelvic-fin origin and on dorsal-fin base. Cleithrum and coracoid totally exposed. Arrector fossae partially enclosed by ventral lamina of coracoids. Abdomen entirely covered by plates (Fig. 7A), abdomen formed by lateral plate series with elongate and large plates, formed by two lateral plates series, similar in size; median plates formed by one to three plates series reaching anal shield. Lateral of body entirely covered by plates (Fig. 7B); mid-dorsal plates poor developed, reaching middle of dorsal-fin base; median plates not interrupted in median portion of body; mid-ventral plates reaching end of dorsal-fin base.

Parts of dorsal head bone plates presented in Fig. 7C. Snout tip formed by one pair of rostral square-shaped plates (r). Nasal (n) almost rectangular forming anterior medial nostril margin in contact posteriorly with frontals (f) and anteriorly and laterally with pre-nasals (pn). Pre-nasals (pn) positioned posteriorly of rostral plates (r), formed by two large and one small square-shaped plates, and one elongate rectangular shaped between nares. Top of head composed by compound pterotic (cpt), parieto supraoccipital (soc) and frontal (f), largest bones of head, and prefrontal (pf) and sphenotic (sp). Compound pterotic (cpt) fenestrated randomly distributed. Lateral surface of head presented in Fig. 7D. Posterior rostrum plates pr1-pr2 small, and rectangular shaped; pr4-pr3 largest, first rectangular and second square-shaped. Infraorbital plate series complete (io1-io5), present just above posterior rostrum series, all covered by latero-sensory canal system; io2 largest and io5 smallest; io3, io4 and io5 forming inferior orbital margin of eyes; preopercle (pop) elongated and rectangular, covered by latero-sensory canal; preopercle present under io4 and io5, and upper cp1, cp2 and op. Subocular cheek plates (cp1-cp2) and opercle (op) form posterior lateral margin of head.

Ground color of dorsal and ventral region of head and trunk pale yellowish. Conspicuous longitudinal dark stripe enlarging from rostral plates to anterior corner of eyes, straightening and bordering on ventral margin of eyes, enlarging again through compound pterotic and lateral series of plates to caudal-fin. Another conspicuous longitudinal dark stripe starting medially at pre-nasal plate region and enlarging on supraoccipital region. Unpigmented portion of snout appears as hyaline v-shaped mark from rostral plate passing through nares to orbital margins. Longitudinal dark stripe from superior portion of sphenotic through mid-dorsal plates to posterior margin of dorsal-fin base. Dark blotch on compound pterotic overlaps mid-dorsal longitudinal dark stripe. Dark saddle on middle portion of predorsal region reaches mid-dorsal longitudinal dark stripe. Overall, pigmentation pattern forms geometric spots on anterodorsal region of body. Three dark saddles usually cross posterodorsal region of body, reaching longitudinal stripe on side of trunk: first saddle at middle of dorsal fin, second at adipose-fin region, and third at end of caudal peduncle. Saddles inconspicuous in some specimens. Ventral region of body almost completely pale yellowish, except few dark spots on caudal peduncle and dark ring at anal-fin origin. Dorsal, pectoral, and pelvic fins with dark chromatophores forming irregular sets of bands: three on dorsal and pectoral fin, and one on pelvic fin. Anal fin with few scattered chromatophores, sometimes forming bands. Caudal fin hyaline, except for dark spot on origin of rays, and dark band on middle of rays (Fig. 6).

Adults males have a papilla in urogenital opening (vs. absent in females); have a longer pelvic fin that extends beyond anal-fin origin (vs. pelvic fin not reaching anal-fin origin in females); and have an unbranched pelvic-fin ray supporting a dermal flap along its dorsal surface. Both sex have a membrane on the anal opening; however, this membrane is more developed in females (Fig. 4B) than in males (Fig. 4E), covering almost the entire urogenital opening.

The species is known from three small tributaries the riacho Águas Claras, riacho Maracaña and riacho São Jorge, all draining to the rio Sepotuba, in the upper rio Paraguay basin (Fig. 5B).

The species name paresi (a noun in apposition), refers to the the Paresí Indians who speak Paresí, a branch of the Aruak language. The Paresí used to live throughout most of Mato Grosso State including the municipality of Santo Afonso. Paresí were also some of the main guides of Marechal Cândido Rondon, the famous Brazilian pioneer in this region of Brazil at the beginning of the 18th century.