Hisonotus thayeri, Martins & Langeani, 2016

Martins, Fernanda O. & Langeani, Francisco, 2016, Redescription of Hisonotus notatus Eigenmann & Eigenmann, 1889 (Loricariidae: Hypoptopomatinae), the type species of the genus, and description of a new species from coastal drainages of southeastern Brazil, Neotropical Ichthyology 14 (2), No. e 150100, pp. 1-18 : 2-8

Hisonotus thayeri , new species

u r n:l sid:z o o b a n k.o r g:a c t: 98850 6F 7-F DB5- 4752-BD C9- 5FF43DCAD47A

Hisonotus notatus Eigenmann & Eigenmann, 1889: 41 (original description; partim, specimens from Juiz de Fora captured during the Thayer expedition).

Fig. 1

Holotype. MNRJ 42382 , 36.7 mm SL, female, Brazil, Espírito Santo State, Guarapari, Rio Grande county near the frontier between Guarapari and Anchieta, rio Benevente drainage, 20º37’29”S 40º37’3”W, 26 Jan 1989, J. L. Helmer, C. Zamprogno & F. Vieira.

Paratypes. All from Brazil. Minas Gerais State: Rio Paraíba do Sul drainage: MNRJ 15937 , 1 , 24.6 mm SL, Volta Grande, rio Paraíba do Sul, downstream of hydroeletric plant UHE Ilhas dos Pombos, ca. 21º51’S 42º36’W, D. F. Moraes Jr. & E. P. Caramaschi. MNRJ 15987 , 7 , 26.1-34.2 mm SL, Volta Grande, rio Paraíba do Sul, downstream of hydroeletric plant UHE Ilhas dos Pombos, ca. 21º51’S 42º36’W, D. F. Moraes Jr. & E. P. Caramaschi. Rio de Janeiro State: Paraíba do Sul drainage: MNRJ 12837 , 2 , 20.3-29.9 mm SL (1, 29.9 mm SL), Resende, rio das Pedras, Penedo (Três Cachoeiras), 22º28’8”S 44º26’48”W, 2 Jul 1982, G. W. A. Nunan, W. D. Bandeira & L. F. M. Silva. MNRJ 14752 , 17 (1 c&s), 27.6- 37.8 mm SL, São Fidélis, affluent to rio Paraíba do Sul, Poço Dantas farm, 25 Oct 1989, D. A. Halboth, N. Viana & E. P. Caramaschi. MNRJ 15544 , 1 , 28.0 mm SL, Teresópolis, rio Paquequer, affluent to rio Preto, rio Piabanha basin, on BR-116 road, ca. 22º28’S 43º0’W, 17 Feb 1990, E. P. Caramaschi, D. F. Moraes Jr. MNRJ 15913 , 18 (1 c&s), 26.8-39.1 mm SL (10, 27.6-39.1 mm SL), São Fidélis, rio Dois Rios , Poço D’Antas farm, ca. 21º38’S 41°51’W, 30 Aug 1989, D. A. Halboth, M. Viana & E. P. Caramaschi. MNRJ 15915 , 6 , 24.7-36.9 mm SL, São Fidélis, rio Dois Rios , D’Antas farm, ca. 21º38’S 41º51’W, 29 Mar 1989, D. A. Halboth, M. Viana & E. P. Caramaschi. MNRJ 15916 , 9 , 28.9-37.3 mm SL, São Fidélis, rio dois Rios, Poço Dantas farm, ca. 21º38’S 41º51’W, 26 Apr 1997, M. Vianna & J. M. Aranha. MNRJ 15923 , 2 , 29.83-31.5 mm SL, Itaperuna, rio Muriaé , near the intersection between BR-356 road and RJ-186 road, ca. 21º15’S 41º45’W, 24 Oct 1989, D. F. Moraes, E. P. Caramaschi & D. A. Halboth. MNRJ 15941 , 11 , 27.6-41.9 mm SL, São Fidélis, rio Dois Rios , Poço Dantas farm, ca. 21º38’S 41º51’W, 29 Mar 1989, D. A. Halboth, M. Vianna & E. P. Caramaschi. MNRJ 15993 , 5 , 23.7-37.8 mm SL, São Fidélis, rio Dois Rios , Poço Dantas farm, ca. 21º38’S 41º51’W, 27 Nov 1989, D. F. Moraes & E. P. Caramaschi. MNRJ 16009 , 1 , 40.4 mm SL, Itaperuna, rio São Domingos , affluent to rio Muriaé , ca. 21º16’S 41º48’W, 25 Jul 1989, D. F. Moraes Jr. & D. A. Halboth. MNRJ 16010 , 4 , 28.3-37.3 mm SL, Itaperuna, rio Muriaé , near the intersection between BR-356 road and RJ-186 road, ca. 21º15’S 41º45’W, 24 Jul 1989, D. F. Moraes Jr. & D. A. Halboth. MNRJ 16056 , 3 , 30.7-36.3 mm SL, São Fidélis, rio Dois Rios , Poço Dantas farm, ca. 21º38’S 41º51’W, 26 Jul 1989, D. A. Halboth, M. Vianna & E. P. Caramaschi. MNRJ 16486 , 1 , 33.3 mm SL, Itaperuna, rio Muriaé , near the intersection between BR-356 road and RJ-186 road, ca. 21º15’S 41º45’W, 2 Nov 1988, D. F. Moraes Jr. & E. P. Caramaschi. MNRJ 16493 , 9 (1 c&s), 15.9-36.3 mm SL (5, 27.5-36.3 mm SL), Itaocara, rio Negro affluent to rio Dois Rios , near the intersection between BR-116 road and RJ- 492 road, ca. 21º45’S 42º0’W, 2 Nov 1988, E. P. Caramaschi & D. F. Moraes Jr. MNRJ 16928 , 5 , 15.6-30.2 mm SL (2, 27.3-30.2 mm SL), Itaperuna, rio Carangola , affluent to rio Muriaé , on BR-356 road, ca. 21º12’S 41º55’W, 1 Nov 1988, D. F. Moraes Jr. & E. P. Caramaschi. MNRJ 28243 , 1 , 28.2 mm SL, Campos dos Goytacazes , rio Muriaé , ca. 21º24’S 41º41’W, 1 Nov 1988, E. P. Caramaschi, D. F. Moraes Jr. et. al. Lagoa Feia drainage: MNRJ 20835 , 5 , 29.5 -42.0 mm SL, Santa Maria Madalena, poço da Mirindiba, rio Sossego , 24 Mar 1998, G. W. A. Nunan, D. F. Moraes & A. Turler. Rio Macaé drainage: MNRJ 30884 , 7 , 19.7-35.1 mm SL, Macaé, rio do Ouro, upstream from cachoeira do Salto, affluent to rio São Pedro , 22º17’15”S 42º0’37”W, 18 Jan 2003, R. P. Leitão, H. J. Farias & L. Borely. MNRJ 39303 , 1 of 13, 35.5 mm SL, Macaé, rio do Ouro, on Bicuda road, 22º17’15”S 42º0’36”W, 25 Sep 2011, P. A. Buckup, C. Quijada & J. C. Pascoli. Espírito Santo State: Rio Itapemirim drainage: MBML 1270, 49, 15.8-33.5 mm SL (6, 26.5-33.5 mm SL); DZSJRP 20157, 8 (4 c&s), 13.4-32.6 mm SL (4, 27.1-32.6 mm SL), Muniz Freire, stream affluent to rio Norte , 20º22’31”S 41º24’41”W, 8 Oct 2001, R. L. Teixeira & G. I Almeida. MBML 2462, 6, 25.4-37.2 mm SL, Alegre, ribeirão São Bartolomeu downstream from Cachoeira Braúna , 20º46’53”S 41º27’12”W, 1 Oct 2009, L. M. Sarmento-Soares, R. F. Martins-Pinheiro, M. R. Britto & F. M. R. S. Pupo. MBML 2472, 5, 26.0- 37.4 mm SL, Cachoeiro de Itapemirim , ribeirão Floresta in Burarama , 20º41’20”S 41º20’24”W, 1 Oct 2009, L. M. Sarmento- Soares, R. F. Martins-Pinheiro, M. R. Britto & F. M. R. S. Pupo. MBML 3674, 8, 32.3-39.6 mm SL, Atílio Vivácqua, affluent to rio Muqui do Norte on ES-489 road (Joaquim Caiado road) between BR-101 road and Atílio Vivácqua, 20º59’9”S 41º10’2”W, 21 Oct 2010, L. M. Sarmento- Soares, R. F. Martins-Pinheiro, M. M. C. Roldi & M. M. Lopes. MBML 3989, 4, 17.9-27.3 mm SL, Muniz Freire, unnamed stream affluent to rio Norte , 20º27’51”S 41º24’47”W, R. L. Teixeira & G. I. Almeida. MNRJ 22984 , 2 , 20.0- 29.6 mm SL, Cachoeiro do Itapemirim , córrego Safra on BR-101 road, 20º53’56”S 41º3’16”W, 26 Aug 2001, P. A. Buckup, A. T. Aranda, F. A. G. Melo, F. P. Silva, G. R. Moyer & R. L. Teixeira. MNRJ 25845 , 23 , 26.0- 31.6 mm SL, Muniz Freire, affluent to rio Norte , 11 Sep 2002, R. L. Teixeira. MNRJ 36634 , 8 , 22.0- 37.5 mm SL, Alegre, ribeirão São Bartolomeu, upstream from cachoeira Braúna, 20º46’53”S 41º27’12”W, 1 Oct 2009, L. Sarmento-Soares, R. Martins-Pinheiro, M. R. Britto & F. M. R. S. Pupo. MNRJ 36651 , 6 , 27.5-39.5 mm SL, Cachoeiro de Itapemirim , ribeirão Floresta in Burarama , 20º41’34”S 41º20’39”W, 1 Oct 2009, L. Sarmento-Soares, R. Martins-Pinheiro, M. R. Britto & F. M. R. S. Pupo. MNRJ 38268 , 10 , 18.2 -32.0 mm SL, Muniz Freire, affluent to rio Norte , 20º27’51”S 41º24’47”W, 8 Oct 2001, R. L. Teixeira & G. I. Almeida. Rio Benevente drainage: MBML 479, 37 (2 c&s), 18.3-37.7 mm SL (7, 29.3-37.7 mm SL); MZUSP 115250 , 5 , 20.8 -38.0 mm SL (3, 32.5-38.0 mm SL), Alfredo Chaves, rio Joéba , 20º48’20”S 40º38’44”W, 2 Mar 2001, R. L. Teixeira & G. I. Almeida. MBML 1120, 7, 30.3-41.6 mm SL, Alfredo Chaves, córrego Cachoeira Alta in Cachoeira Tororama , 20º38’06”S 40º44’58”W, 2 Mar 2001, R. L. Teixeira & G. I. Almeida. MBML 1377, 26, 6.8-31.1 mm SL (7, 26.8-31.1 mm SL), Alfredo Chaves, córrego Cachoeira Torama, 20º38’6”S 40º44’58”W, 29 Jul 2005, R. L. Teixeira. MBML 3157, 20, 21.0- 37.7 mm SL, Guarapari , Rio Grande county near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 10 Mar 1989, J. L. Helmer & F. Vieira. MBML 3166, 17, 20.7-29.0 mm SL, Guarapari , Rio Grande county near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 13 May 1989. MBML 3169, 40, 25.8-40.5 mm SL (9, 28.1-40.5 mm SL), collected with holotype. MBML 3196, 21, 17.2-31.6 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 10 Mar 1989, J. L. Helmer & F. Vieira. MBML 3223, 6, 25.1-27.8 mm SL, Guarapari , Rio Grande , near to Jaqueira in the frontier between Guarapari and Anchieta, 6 Jan 1989, J. L. Helmer, C. Zamprogno & F. Vieira. MBML 3259, 35, 24.4-34.8 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 10 Mar 1989, J. H. Helmer & F. Vieira. MBML 3261, 12, 24.4-35.9 mm SL, Guarapari , Rio Grande near to Jaqueira in the frontier between Guarapari and Anchieta, 6 Jan 1989, J. L. Helmer, C. Zamprogno & F. Vieira. MBML 3269, 22 (2 c&s), 13.5- 33.3 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 13 May 1989,. MBML 3398, 3, 29.6-40.9 mm SL, Alfredo Chaves, rio Caco de Pote near Caco de Pote village , 20º36’30”S 40º43’16”W, 22 Jun 2010, M. M. Martinelli. MNRJ 38265 , 2 , Alfredo Chaves, córrego Torotoma, Cachoeira Alta, 20º38’6”S 40º44’59”W, 2 Mar 2001, R. L. Teixeira & G. I. Almeida. MNRJ 39186 , 6 , 22.6-25.7 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 10 Mar 1989, J. L. Helmer & F. Vieira. MNRJ 39200 , 5 , 17.5-25.4 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 10 Mar 1989, J. L. Helmer & F. Vieira. MNRJ 39192 , 6 , 25.1-28.2 mm SL, Guarapari , Rio Grande near the frontier between Guarapari and Anchieta, 26 Jan 1989, J. L. Helmer, C. Zamprogno & F. Vieira. MNRJ 39191 , 6 , 14.9-25.3 mm SL, Gurapari, Rio Grande near the frontier between Guarapari and Anchieta, 20º37’29”S 40º37’3”W, 11 Mar 1989, J. L. Helmer & F. Vieira. Rio Itabapoana drainage: MBML 1766, 3, 26.8- 33.0 mm SL, Mimoso do Sul , ribeirão das Flores, 21º3’51”S 41º21’59”W, 3 Dec 2002, R. L. Teixeira & G. I. Almeida. MBML 1770, 6, 26.1-39.9 mm SL, Mimoso do Sul , córrego Boa Vista, 21º3’51”S 41º21’59”W, 3 Dec 2002, R. L. Teixeira & G. I. Almeida. MBML 3716, 1, 18.3 mm SL, Mimoso do Sul , córrego da Braúna, on ES-319 road (Rubens Rangel road) between Mimoso do Sul and BR- 101 road, 21º06’14”S 41º19’21”W, 22 Oct 2010, L. M. Sarmento-Soares, R. F. Martins-Pinheiro, M. M. C. Roldi, M. M. Lopes & M. M. Martinelli. MBML 3728, 13 (1 c&s), 16.2-30.8 mm SL (11, 24.9-30.8 mm SL), Mimoso do Sul , ribeirão das Flores, on José Alves Toledo Road between BR-101 and São José das Torres, 21º04’18”S 41º13’44”W, 22 Oct, 2010, L. M. Sarmento-Soares, R. F. Martins-Pinheiro, M. M. C. Roldi, M. M. Lopes & M. M. Martinelli. MBML 3786, 10, 29.4-41.4 mm SL, Mimoso do Sul , córrego do Farol, affluent to rio Preto , on BR-101 road, 21º7’10”S 41º44’34”W, 26 Aug 2001, P. A. Buckup, A. T. Aranda & F. A. G. Melo. MBML 4080, 1 c&s, Mimoso do Sul , ribeirão das Flores, on José Alves Toledo Road between BR-101 road and São José das Torres, 21º04’18”S 41º13’44”W, 22 Oct 2010, L. M. Sarmento- Soares, R. F. Martins-Pinheiro, M. M.C. Roldi, M. M. Lopes & M. M. Martinelli. MNRJ 23006 , 207 , Mimoso do Sul , córrego do Farol, affluent to rio Preto , on BR-101 road, 21º4’34”S 41º13’59”W, 26 Aug 2001, P. A. Buckup, A. T. Aranda, F. A. G. Melo, F. P. Silva, G. R. Moyer & R. L. Teixeira. Rio Novo drainage: MBML 3362, 11, 11.5- 28.1 mm SL (3, 24.2-28.1 mm SL), Rio Novo do Sul , córrego São Gabriel, affluent to córrego São Vicente de Baixo , 25 Apr 2010, M. M. Martinelli. Rio Doce drainage: MCP 34393, 1 , 28.6 mm SL, Itarana, córrego Limoeiro, affluent to rio Santa Joana , 19º54’48”S 40º50’10”W, 8 Nov 2001, R. L. Teixeira .

Non-types. MCZ 8177 , 1 , 30.5 mm SL, paralectotype of Hisonotus notatus , Brazil, Minas Gerais, Juiz de Fora, rio Paraíba do Sul drainage, ca. 21º47’S 43º23’W, 21 Jun 1865, L. Agassiz & J. Whitaker .

Diagnosis. Hisonotus thayeri differs from H. aky , H. brunneus , H. carreiro , H. charrua , H. heterogaster , H. laevior , H. megaloplax , H. montanus , H. nigricauda , H. notopagos , H. ringueleti , H. taimensis , and H. vireo by having the anterior portion of snout completely covered by odontodes ( Figs. 2b, d ) (vs. anterior portion of snout with an odontode-free band between the dorsal and ventral series of odontodes). It distinguishes from H. alberti , H. depressicauda , H. depressinotus , H. francirochai , H. maculipinnis , H. packysarkos , H. paulinus , and H. prata by having the anterior portion of abdomen covered by large plates arranged in three longitudinal series without naked spaces between them (vs. abdominal plates, when present, not arranged in three longitudinal series, or when arranged with naked spaces between the lateral and median series). It differs from H. acuen , H. bockmanni , H. chromodontus , and H. vespuccii by having an ovoid to rectangular spinelet (vs. spinelet V -shaped, with lateral projections anteriorly directed). It can be distinguished from H. iota and H. leucophrys by the absence of well-developed odontodes at the posterior tip of supraoccipital (vs. presence). It differs from H. armatus and H. hungy by having 28 vertebrae (vs. 25-26 in H. hungy and 29 in H. armatus ). It distinguishes from H. leucofrenatus by having the clear longitudinal stripe of head ending near the vertical through distal tip of opercle (vs. clear longitudinal stripe longer, bifurcating at the tip of compound pterotic and running parallel to each other; the inferior stripe over the canals of the lateral line, reaching the vertical through the middle of dorsalfin base); bifid neural spine of seventh vertebra present, dorsolaterally projected (vs. bifid neural spine absent); and basipterygia contacting along midline until anterior margin (vs. anterior portion of basipterygia with halves apart from each other). Finally, H. thayeri differs from H. notatus by having the mid-dorsal series of plates generally continuous, with a total of 15-18 plates (mode 17), rarely with one plate lacking in the middle of the series ( Fig. 3 ) (vs. mid-dorsal series generally interrupted, with 4-13 plates present, and 5-8 lacking plates in the middle of the series).

Description. Morphometric and meristic data in Tables 2 and 3. Dorsal body profile ascending from snout to vertical through posterior edge of eye; slightly convex to dorsal-fin insertion; descending at dorsal-fin base; almost straight to caudal-fin origin, except by small elevation in region of dorsal procurrent rays. Males with dorsal profile generally flattened, sometimes straight from vertical through posterior edge of nostril to caudal-fin origin (as in H. notatus , Fig. 4 ). Ventral body profile almost straight from snout to pelvic-fin insertion; slightly ascending at pelvicfin base; straight to caudal-fin origin, except by slight descent in region of ventral procurrent rays. Greatest body depth at dorsal-fin origin. Greatest body width at opercular opening, gradually tapering towards snout and caudal fin, in dorsal view. Caudal peduncle almost ellipsoid in transverse section.

Anterior margin of snout rounded in dorsal view; tip of snout with single large rostral plate, its posterior margin with U -or V -shaped concavity; well-developed odontodes completely covering ventral and dorsal portions of rostral plate, postrostral plate 1, and lateroventral margin of head ( Figs. 2b, d ). Remaining odontodes of head and body small, randomly distributed, not forming conspicuous rows, crests or tufts. Eye small, dorsolaterally placed, not visible in ventral view. Iris operculum present. Compound pterotic fenestrae variable in size, small on laterodorsal and large on lateroventral portions; its posterior extension mediumsized and rounded, not surpassing rib of sixth vertebra; infraorbital canal entering infraorbital series via sphenotic. Parieto-supraoccipital not forming part of dorsal wall of swimbladder capsule.

Body entirely covered by dermal plates, except on ventral part of head, region overlying opening of swimbladder capsule, pelvic-fin origin, and urogenital pore. Abdomen completely covered by large plates; anterior plates arranged in three longitudinal rows, sometimes unaligned, the lateral rows with 1-5(3) plates; posterior plates, between pelvic fins, randomly distributed.

Lips oval, papillose; lower lip fringy, larger than upper, falling short of pectoral girdle; papillae gradually smaller towards lip edge. Maxillary barbel reduced, free from oral disk. Teeth slender and bifid; median cusp larger and rounded, lateral smaller and pointed. Premaxillary and dentary accessory teeth absent, even in smallest examined specimen (13.3 mm SL).

Dorsal fin originating approximately at vertical through end of pelvic-fin base; tip of adpressed rays surpassing vertical line at end of anal-fin base. Spinelet small, ovoid, inserted in notch in nuchal plate; locking mechanism non-functional. Nuchal plate exposed area rectangular to pentagonal. Anterior portion of compound supraneural first dorsal-fin proximal radial contacting neural spine of seventh vertebra. Pectoral fin originating immediately behind opercular opening; tip of adpressed rays almost reaching vertical through urogenital opening; well-developed odontodes on unbranched ray, gradually enlarged towards tip. Cleithrum and coracoid almost totally exposed, with many odontodes, except for arrector fossa region covered by skin only. Arrector fossa almost completely enclosed by ventral lamina of coracoid and cleithrum, opening restricted to small anterior area near midline. Pectoral axillary slit present in juveniles and adults, large, about 1.3-1.7 times in orbital diameter, at angle of 45° with body axis. Pelvicfin unbranched ray shorter than branched ones. Anal-fin first proximal radial contacting haemal spine of 12th or 13th vertebrae. Caudal fin concave, lower lobe slightly longer than upper. Adipose fin and azygous plates absent.

Five lateral series of plates ( Fig. 3b ). Dorsal series complete from posterior edge of supraoccipital to caudalpeduncle end. Mid-dorsal series long, rarely with missing intermediate plates. Median series from compound pterotic to caudal-fin base; in general, 1-3 plates lacking and/or 1-2 non-perforated plates in middle portion of series, near vertical through dorsal-fin base, and 1-4 non-perforated plates at end of series; first plate, sometimes also second, restricted to sensorial canal, occasionally fused to compound pterotic. Mid-ventral series long, from lateral process of cleithrum to vertical through tip of adpressed anal fin. Ventral series from near middle or end of pelvic-fin length to caudal-peduncle end.

Color in alcohol. Dorsal profile medium brown; dorsal area of head dark brown from tip of snout to median portion of supraoccipital. Three dorsal inconspicuous saddles: first at dorsal-fin base; second at end of dorsalfin length; third at end of caudal peduncle. Clear stripe extending from tip of snout to near vertical through distal tip of opercle, passing by dorsal margin of postrostral plates 1 and 2, external edge of nostril, limits between prefrontal and infraobitals 2 and 3, and dorsal margin of orbit. Lateral profile of body homogeneously medium brown, except for yellowish lateroventral portion of head and lateral process of cleithrum, sometimes with spots forming vermiculated pattern. Ventral portion of body yellowish.

Membranes of dorsal, anal, pectoral, and pelvic fins hyaline, pigmented areas of rays arranged in interspersed bars forming transversal bands. Caudal fin densely pigmented, except for slender unpigmented edge and hyaline areas in both lobes: superior lobe with oblique blotch from posteromedial portion of unbranched ray to distal portion of median rays, and other at superior tip of lobe, these two areas separated by dark inclined line; inferior lobe with small posteromedial area restricted to unbranched ray and last branched ray, and another at inferior tip of lobe.

Sexual dimorphism. Males in general smaller and with dorsal profile more depressed than females (as in H. notatus , Fig. 4 ), the latter feature being rare among Hypoptopomatinae species, and reported for the first time here. Males have conspicuous urogenital papilla immediately posterior to anus, expanded flap of skin on dorsal surface of the first pelvic-fin ray, and tip of adpressed pelvic fin generally reaching anal-fin origin. Nasal chamber of males generally enlarged, its width 12.1- 16.4% in HL (mean 14.1%) [vs. 9.3-12.6% (mean 10.8%) in females], and its length 15.1-20.9% in HL (mean 17.9%) [vs. 11.3-17.4% (mean 14.2%) in females].

Distribution. The species occurs in the coastal basins of rio Paraíba do Sul, Lagoa Feia, rio Macaé, rio Itabapoana, rio Itapemirim, rio Novo, rio Benevente, and rio Doce, in Minas Gerais, Rio de Janeiro and Espírito Santo states ( Fig. 5 ).

Etymology. The specific epithet thayeri is named after the Thayer Expedition, realized in the middle of the 19th century and considered one of the most important journeys performed in Brazil, during which the species was sampled for the first time. A genitive.

Conservation status. Hisonotus thayeri is a common and abundant species in the sampling sites, widely distributed in the coastal basins of rio Paraíba do Sul, Lagoa Feia, rio Macaé, rio Itabapoana, rio Itapemirim, rio Novo, rio Benevente, and rio Doce, with extent of occurrence (EOO) of approximately 42,105 km 2. As today we did not recognize any threats that may endanger it and the species population is apparently stable, according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2014), Hisonotus thayeri can be classified as Least Concern (LC).

Figures

Fig. 1. Hisonotus thayeri, new species, MNRJ 42382, holotype, 36.7 mm SL, female, Brazil, Espírito Santo State, Guarapari Municipality, rio Benevente drainage.

Fig. 2. Scanning electron micrographs of tip of snout of Hisonotus notatus, DZSJRP 13852, 34.6 mm SL (a, c) and Hisonotus thayeri, MNRJ 14752, 38.4 mm SL, paratype (b, d).

Fig. 3. Lateral plates of trunk of Hisonotus notatus, DZSJRP 13852, 31.5 mm SL, male (a) and Hisonotus thayeri, DZSJRP 20157, paratype, 32.4 mm SL, female (b), left side. Scale bars = 1mm.

Fig. 4. Sexual dimorphism in body depth in Hisonotus notatus, MNRJ 38147, female, 37.2 mm SL (above), and male 32.3 mm SL (below).

Fig. 5. Geographic distribution of Hisonotus notatus (black squares, and star for type locality) and Hisonotus thayeri (red dots, and triangle for type locality) in southeastern Brazilian costal drainages. Symbols can represent more than one sampling locality.