A new species of Hisonotus (Siluriformes, Loricariidae) from rio São Francisco basin, Brazil

Abstract A new species of Hisonotus is described from the rio São Francisco basin. The new species can be distinguished from congeners by having (1) a unique coloration pattern of caudal fin with one black spot extending from its origin to the ventral lobe and two dark spots at the end of the lobe’s rays; (2) odontodes forming longitudinally aligned rows on head and trunk; (3) a functional V-shaped spinelet; (4) a single rostral plate at the tip of the snout; (5) by lacking contrasting dark geometric spots on the anterodorsal region of the body; (6) a lower caudal-peduncle depth; and (7) lower counts of the lateral median plates and (8) higher premaxillary and dentary teeth. The new species is the second described species of the genus Hisonotus in the rio São Francisco basin. It was found inhabiting the marginal vegetation of the rio São Francisco and three of its tributary, rio das Velhas, rio Paraopeba and rio Formoso.

Within the Otothyrinae, the genus Hisonotus Eigenmann & Eigenmann, 1889 (type species H. notatus Eigenmann & Eigenmann, 1889) was resurrected by Schaefer (1998) with the following combination of characters: snout plates in the anterior portion of the nostril reduced or absent, the rostrum having enlarged odontodes, and the lateral rostral margin composed of thickened plates. However, Britski and Garavello (2007) considered the rostrum with enlarged odontodes as a character very polymorphic and present in several other genera and species of Otothyrinae, as in species of Parotocinclus Eigenmann, 1889. Furthermore, Britski andGaravello (2007) suggested that the other two characters are not satisfactory to define the genus Hisonotus.
Currently, Hisonotus contains 34 valid species, 19 of which were described in the past decade (Eschmeyer 2014), representing an increase of 127% of the diversity of this genus. Herein, we add a new species to the genus Hisonotus found during recent collection expeditions to the rio São Francisco basin. This is the second species of the genus described from this hydrographic system.

Material and methods
Measurements and counts were taken from the left side of the fish, and were made from point to point to the nearest 0.1 mm with a digital caliper. Abbreviations used in the text and the measurements followed Carvalho and Reis (2009). 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 and the compound caudal centrum (PU1 + U1) as one element. Dorsalfin ray counts include the spinelet as the first unbranched ray. Institutional acronyms follow Fricke and Eschmeyer (2014 Diagnosis. Hisonotus vespuccii differs from the congeners by having a unique coloration pattern of caudal fin with one black spot extending from its origin to the ventral lobe and two dark spots at the end of the lobe`s rays and the following combination of character states (none is unique): odontodes forming longitudinally aligned rows (one odontode after the other, but not necessarily forming parallel series) on head and trunk; a functional V-shaped spinelet; the presence of a single rostral plate at tip of the snout; the lack of contrasting dark geometric spots on the anterodorsal region of the body; a low caudal peduncle (depth 6-8% SL); few lateral median plates (21-23); and numerous premaxillary and dentary teeth (13-21 and 11-21, respectively).
Description. Counts and measurements are presented in Table 1. Maximum body size 35.7 mm SL. Dorsal profile of head, in lateral view, slightly convex from snout tip to margin of posterior naris; strongly convex to posterior margin of parieto-supraoccipital; and almost straight to dorsal-fin origin. Dorsal profile of trunk, in lateral view, straight and descending from dorsal-fin origin to insertion of caudal-fin. Ventral profile, in lateral view, straight from snout tip to anal-fin origin; concave and ascending to caudal-fin insertion. Greatest body depth at dorsal-fin origin (14−18% SL). Greatest body width at cleithral region (21−25% SL), progressively narrowing towards to both snout and caudal fin. Cross-section of body between pectoral and pelvic fins dorsally rounded and ventrally flat; cross-section of caudal peduncle ellipsoid, rounded laterally and almost flat dorsally and ventrally.
Head rounded in dorsal view; snout round and 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. Head without conspicuous crests. Some specimens with a poor developed tuft of odontodes in posterior portion of parieto-supraoccipital. Eyes small (13-17% HL), dorsolaterally positioned. Iris operculum present and developed. Premaxillary teeth 13-21; dentary teeth 11-21. Teeth bifid, major  (medial) cusp large and rounded, minor (lateral) cusp minute and pointed. Accessory patch of teeth absent on dentary and premaxilla. Oral disk oval, covered with papillae uniformly distributed on base of dentary and premaxilla and slightly decreasing in size distally. Lower lip larger than upper lip; its border fringed. Maxillary barbel present and joined to lower lip. Presence of conspicuous V-shaped buccal papilla located immediately anterior to buccal valve. Tip of snout with large rostral plate.
Dorsal fin II,7; its origin slightly posterior to pelvic-fin origin. Tip of adpressed dorsal fin surpassing vertically through end of anal-fin origin. Dorsal-fin spinelet short and V-shaped; dorsal-fin lock functional. Pectoral fin I,6; its tip reaching middle of pelvic-fin length when depressed. Pectoral-axillary slit present between pectoral-fin insertion and lateral process of cleithrum. Pectoral spine supporting sharp odontodes on dorsal and ventral surfaces (well developed posteriorly). Pelvic fin I,5; its tip reach-   ing anal-fin origin when depressed in males and far from reaching anal-fin origin in females. Pelvic-fin unbranched ray with dermal flap along its dorsal surface in males. Pectoral spine supporting sharp odontodes on ventral surface turned mesially.
Anal fin i,5; its tip reaching seventh or eighth plate from its origin. Caudal-fin i,7-7,I; distal margin forked. Adipose fin absent. Total vertebrae 27 (in 7 c&s specimens). Body almost entirely covered by bone plates, except on ventral portion of head, around pectoral-and pelvic-fin origins, on dorsal-fin base and area around anus. Abdomen partially covered by bony plates randomly distributed and surrounded by naked areas (in some specimens abdomen is completely covered by bony plates). Laterally, body completely covered by plates; mid-dorsal and mid-ventral plate series well developed reaching vertical through half of caudal peduncle; median plate series continuous in median portion of body. Coracoid and cleithrum completely exposed, covered with odontodes. Arrector fossae partially enclosed by ventral lamina of coracoids.
Color in alcohol. Ground color of dorsal surface of head and body dark gray to lighter brown (juveniles lighter than adults). Ventral surface light brown to yellow in juveniles. All body and fins covered by scattered chromatophores, more visible on ventral portions and around fins insertions (Fig. 1). Caudal-fin hyaline, except for one black spot at its origin extending to ventral lobe and two dark spots at end of rays (Fig.  2a). In some specimens, caudal-fin with chromatophores irregular distributed and sometimes badly forming two dark strips (more visible in juveniles). Neither variation nor variability of caudal-fin coloration patter found in samples we examined (holotype and 249 specimens widely distributed in rio São Francisco basin) with specific emphasis to variability between populations and variation depending on feeding. Color in life. Similar to pattern described for alcohol individuals, but with ground color light green (Fig. 3).
Sexual dimorphism. Adult males distinguished from females by five characters: (1) presence of a papilla at urogenital opening in males (vs. papilla absent in females); (2) pelvic-fin extending beyond anal-fin origin in males, mean 19% SL (vs. pelvic fin far from reaching anal-fin origin in females, mean 17% SL); (3) unbranched pelvic-fin ray supporting a dermal flap (flap slightly wider in basal portion and progressively narrowing distally) on proximal dorsal surface in males (vs. dermal flap absent in females); (4) nares opening wider in males (13-18% HL) than females (10-13% HL); (5) body size smaller in males (mean 26 mm SL) and larger in females (mean 30 mm SL). See Table 1 for values of morphometric characters between males and females.
Habitat and distribution. Hisonotus vespuccii was found associated with marginal vegetation (Fig. 4) in the rio São Francisco and in three of its tributaries, rio das Velhas, rio Paraopeba and rio Formoso (Fig. 5). The new species seems to be abundant through all rio São Francisco basin.
Etymology. The specific name "vespuccii" comes from Italian and is in reference to Américo Vespúcio (Amerigo Vespucci in Italian), navigator and explorer to whom is attributed the discovery of the rio São Francisco in 1501.

Comparative remarks and discussion
The new species H. vespuccii has one character proposed by Schaefer (1998) to diagnose the genus Hisonotus: the rostrum with enlarged odontodes. Moreover, the new species also shares three characters with many species of Hisonotus: a single rostral plate on the tip of the snout, an arrector fossae partially enclosed by a ventral lamina of the coracoid, a character also used by Schaefer (1998) as synapomorphy of all Otothyrini except the New Taxon 3, and a functional V-shaped spinelet. This last character was firstly proposed by Carvalho and Datovo (2012) with pers. comm. of Roberto E. Reis, and posteriorly was reported by Silva et al. (2014) as a possible synapomorphy that may help delimit a new genus within Hisonotus. However, to better understand the relationship of the new species with other species assigned to Hisonotus a phylogenetic analysis is still necessary.
We used seven characters to distinguish the new species H. vespuccii from congeners. The first character was the caudal fin with one black spot extending from its origin to the ventral lobe and two dark spots at the end of the lobe's rays, a pattern unique among Hisonotus species (see Fig. 2b-u for caudal-fin coloration pattern of some species of Hisonotus). Britski and Garavello (2007) discussing about the coloration pattern of the teeth in H. chromodontus Britski & Garavello, 2007 suggested that this aspect of the organism could be a result of physiological features changing according to the individual's foraging success and physiological efficiency, as well as according to the characteristics of the water where the species lives. However, the pattern of caudal-fin coloration seems to be conserved among species of Hisonotus (Fig. 2), with a pattern varying more drastically in H. acuen Silva, Roxo & Oliveira, 2014, a species widely distributed through headwaters of the rio Xingu basin (see Fig. 5 in Silva et al. 2014). In H. vespuccii, the pattern of the caudal-fin with one black spot extending from its origin to the ventral lobe and two dark spots at the end of the lobe`s rays is present in the holotype and the 249 paratypes analyzed.
Members of Loricariidae are known to have intense sexual dimorphisms (Py-Daniel and Fernandes 2005) as we can observe in species of the genera Ancistrus Kner, 1854 (Sabaj et al. 1999), Neoplecostomus Eigenmann & Eigenmann, 1888(Zawadzki et al. 2008Roxo et al. 2012;Andrade and Langeani 2014), Pareiorhaphis Miranda Ribeiro, 1918a(Pereira et al. 2007, Hisonotus , Hypostomus Lacepède, 1803 and Chaetostoma Tschudi, 1846 (Nomura andMueller 1980;Lopez and Roman-Valencia 1996), Farlowella Eigenmann, 1889 (Retzer andPage 1996) and many other. In H. vespuccii, we observed five sexual dimorphic characters: the presence of a papilla at the urogenital opening, a pelvic-fin that extends beyond the anal-fin origin, the unbranched pelvic-fin ray supporting a dermal flap on their proximal dorsal surface, the nares opening wider and a body size that seems to be smaller in males than in females. The first three characters are very common among species of Hisonotus, however differences in size of nares were only previously reported in the original description of H. piracanjuba  and differences in body size in H. ringueleti . Carvalho and Reis (2009) reported that the presence of the dermal flap on proximal dorsal surface of pelvic-fin on males is a plesiomorphic character shared among most members of Otothyrinae and that the derived condition evolved several times within this subfamily at the genera Schizolecis Britski & Garavello, 1984, Epactionotus Reis & Schaefer, 1998, and within Hypoptopomatinae in Acestridium Haseman, 1911, Oxyropsis Eigenmann & Eigenmann, 1889and Hypoptopoma Günther, 1868.