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Description of two new species of Hisonotus Eigenmann & Eigenmann, 1889 (Ostariophysi, Loricariidae) from the rio Paraná-Paraguay basin, Brazil

Abstract Two new species of Hisonotus are described from the rio Paraná-Paraguay basin in Brazil. The most remarkable features of the new species are the odontodes forming longitudinally aligned rows (one odontode after the other, but not necessarily forming parallel series) on the head and trunk (vs. odontodes not forming longitudinally aligned rows), a pair of rostral plates at the tip of the snout (vs. a single rostral plate), the functional v-shaped spinelet (vs. spinelet non-functional, square-shaped, or absent). These features suggest close phylogenetic relationships with Hisonotus bockmanni, H. insperatus, H. luteofrenatus and H. piracanjuba. Additionally, both new species are distinguished from their congeners by characters related to head length and depth, orbital diameter, suborbital depth, caudal peduncle depth, pectoral-fin spine length, snout length and counts of teeth. Hisonotus paresi sp. n. further differs from its congeners by having contrasting dark geometric spots on the anterodorsal region of the body, a character lacking in H. oliveirai sp. n. The variation in number and shape of the rostral plate, posterior rostrum plates, infraorbitals and the preopercle in both new species and in H. insperatus are discussed.


Introduction
Hypoptopomatinae is composed of 19 genera and about 135 valid species (Eschmeyer and Fong 2013). This group includes Hisonotus Eigenmann & Eigenmann, 1889, which has as type species H. notatus Eigenmann & Eigenmann, 1889. Regan (1904 considered Hisonotus to be a synonym of Otocinclus Cope, 1871. This taxonomy had been followed until Schaefer (1998a), who resurrected Hisonotus and listed the following combination of diagnostic characters: reduced or absent snout plates anterior to the nostril, the rostrum with enlarged odontodes, and thickened plates forming the lateral rostral margin. Additional characters used to distinguish Hisonotus from other genera of Hypoptopomatinae include a rostrum with enlarged odontodes and thickened plates forming the lateral rostral margins; the latter character is also present in some other species of Hypoptopomatinae, especially in species of Microlepidogaster Eigenmann &Eigenmann, 1889 (Britski andGaravello 2007).

Material and methods
All measurements and counts were taken from the left side of the fish. Measurements were made from point to point to the nearest 0.1 mm with a digital caliper. Body plate and osteology nomenclature follows Schaefer (1997) and measurements follow Carvalho and Reis (2009) as shown in Table 1. Abbreviations used in the text followed Carvalho and Reis (2009). Morphometrics are given as percentages of standard length (SL), except for subunits of the head region that are expressed as percentages of head length (HL). Specimens were cleared and double stained (c&s) according to the method of Taylor and Van Dyke (1985). Vertebral counts also include the five vertebrae that comprise the Weberian apparatus. Dorsal-fin ray counts include the spinelet as the first unbranched ray. All examined specimens were collected according to the Brazilian laws, and are deposited under permanent scientific collection licenses. After collection, specimens were euthanized using 1% benzocaine in water, fixed in 10% formaldehyde and preserved in 70% alcohol. All Britski & Garavello, 2003, H. luteofrenatus and H. 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 Description. 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 parietosupraoccipital, 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 pelvicfin 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 dorsalfin base; median plates series continuous in median portion of body; mid-ventral plates reaching vertical through end of dorsal-fin base.

Coloration in alcohol.
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).
Sexual dimorphism. 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.
Distribution. 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).
Etymology. 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.
Description. 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.
Coloration in alcohol. 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 caudalfin. 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).
Sexual dimorphism. 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.
Distribution. 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).
Etymology. 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.

Discussion
Hisonotus oliveirai is externally similar to H. insperatus and H. piracanjuba both species from upper stretches of the rio upper rio Paraná basin, H. paresi resembles more closely to H. bockmanni from the rio Tapajós basin. Hisonotus insperatus, H. chromodontus, H. luteofrenatus, and H. oliveirai have conspicuous odontodes forming well defined and widely spaced rows on the head and trunk (the main character used to distinguish theses species), while H. paresi has smaller, less conspicuous odontodes that form closely spaced rows (Fig. 2) Britski & Garavello, 1993, Moenkhausia phaeonota Fink, 1979, Hyphessobrycon vilmae Géry, 1966, and Aequidens rondoni Miranda-Ribeiro, 1918, Parodon nasus Kner, 1859, Hemiodus semitaeniatus Kner, 1858 are other examples of fishes occurring in the upper rio Paraguay basin, as well as in the upper rio Tapajós basin. Also, Batrochoglanis melanurus Shibatta & Pavanelli, 2005, which occurs at the upper rio Paraguay, appears to have its sister-taxon in the rio Tapajós basin. According to Hubert and Renno (2006) and Lima et al. (2007) these examples suggest that there may be a dispersal route between the upper rio Tapajós and the upper rio Paraguay basins. Carvalho and Datovo (2012) reported a functional V-shaped spinelet as a character shared among H. bockmanni, H. chromodontus, H. insperatus and H. luteofrenatus, and this character is also present in Hisonotus oliveirai and H. paresi. They suggested that this is apparently synapomorphic within Hisonotus, and suggested that those species could compose a new monophyletic genus within the Hypoptopomatinae.
Hisonotus paresi has an unusual coloration pattern with contrasting dark stripes and bands converging to form geometric spots on the anterodorsal region of body, which is more similar in coloration to species of Otocinclus than to Hisonotus. However, H. paresi is morphologically similar to nominal species already assigned to Hisonotus, rather than to any other Hypoptopomatinae species. Additionally, H. paresi and H. oliveirai exhibit one of the diagnostic characters used to define Hisonotus in its resurrection by Schaefer (1998a) Osteological characters are known to be conservative within Hypoptopomatinae species compared to external anatomy (Schaefer 1987(Schaefer , 1997(Schaefer , 1998bGaravello 1977;Mo 1991;de Pinna 1998;Diogo et al. 2001;Ribeiro et al. 2005). Britski and Garavello (2003) used the presence of a pair of rostral plates in the snout tip to diagnose Hisonotus insperatus. Martins and Langeani (2012) also used that same character to distinguish H. piracanjuba. This character is present in both H. oliveirai and H. paresi. However, our results showed that the number and shape of head plates can be highly variable among specimens of a given species. We analyzed 18 cleared and stained specimens of H. insperatus from rio Capivara and rio Araquá from Botucatu, São Paulo State. Three individuals of H. insperatus had a single rostral plate, instead of a pair of rostral plates, however, all specimens of H. oliveirai and H. paresi had a pair of rostral plates. Variation in plate shape and number was further found in other head plates, including the posterior rostrum plates, infraorbitals and preopercle plate (red arrows in Fig. 8). For instance, the same specimen might have the fourth infraorbital divided in the right side, but not in the other left side Fig. 8C. This bilateral asymmetry was also found in a paratype of H. oliveirai (NUP 9839, 23.7 mm SL). Moreover, the first infraorbital of both sides might reach the ventral margin of the rostrum, among the second and third posterior rostrum plates (Fig. 8 A, B), or not (Fig. 8C, D). Additionally, the size of the first infraorbital is variable among the specimens of H. insperatus and H. oliveirai. A similar pattern of variation was observed on posterior rostrum plates: the first and second posterior rostrum plates appear to be split only in the left side of the specimen (Fig. 8C, D), increasing the number of posterior rostrum plates to six, versus four in the right side. Finally, an extra plate is found among preopercle and compound pterotic perforated to infraorbital canal of the specimen of Fig. 8C, D, but not in the remaining specimens.