Description of a new species of Parotocinclus (Siluriformes, Hypoptopomatinae) from the rio Tapajós basin

Abstract A new species of Parotocinclus is described from three small tributaries of the rio Tapajós basin, Mato Grosso State, Brazil. The new species can be distinguished from its congeners by presenting the following characters: (1) a triangular dark blotch at the anterior base of the dorsal fin, (2) the absence of an adipose fin but presence of one small platelet at typical adipose-fin region, (3) the abdomen completely covered by dermal plates, (4) a pectoral girdle totally exposed, (5) a single series of bicuspid teeth, and (6) the higher number of bicuspid premaxillary and dentary teeth.


Introduction
The subfamily Hypoptopomatinae currently includes the tribes Otothyrini, Neoplecostomini, and Hypoptopomatini (sensu Lujan et al. 2015) and is one of the most diversified and widespread groups of the Neotropical family Loricariidae, with about 210 species according to Eschmeyer and Fong (2016). Within Otothyrini, the genus Parotocinclus initially described by Eigenmann and Eigenmann (1889) as a subgenus of Hisonotus Eigenmann & Eigenmann, 1889 to include the species Otocinclus maculicauda Steindachner, 1887, presents 28 species (Eschmeyer 2016).
Recently, as a result of molecular studies, the genus Parotocinclus was recognized as non-monophyletic with several species more related to species assigned to other Otothyrini genera, mainly Hisonotus, than to the type species Parotocinclus maculicauda (e.g. Cramer et al. 2011;Roxo et al. 2014;Silva et al. 2016). This genus is distributed through almost all hydrographic systems in South America from the Guyana Shield drainages and Amazon Shield tributaries to the coastal drainages of eastern and southeastern Brazil, including the rio São Francisco basin (Sarmento-Soares et al. 2009;Lehmann et al. 2014Lehmann et al. , 2015. Lehmann et al. (2014Lehmann et al. ( , 2015 proposed that several species included in Parotocinclus, namely: P. amazonensis Garavello, 1977;P. britskii Boeseman, 1974; P. collinsae Schmidt & Ferraris, 1985;P. eppleyi Schaefer & Provenzano, 1993;P. halbothi Lehmann, Lazzarotto & Reis, 2014; P. longirostris Garavello, 1988;P. polyochrus Schaefer, 1988;and P. variola Lehmann, Schvambach & Reis, 2015, could be part of a new genus. These authors suggested that this possible new genus could be diagnosed by (1) the presence of a triangular dark blotch at the anterior base of the dorsal fin; (2) a canal cheek plate on the ventral surface of head elongated posteriorly and contacting the cleithrum; and (3) the head and snout being elongated and with a Y-shaped, white or cream colored mark dorsally.
Here, we recognized a new Otothyrini species as a result of collection efforts in the rio Tapajós basin. The new species is described below in the genus Parotocinclus, but we will not be surprised if this new entity is reallocated into a new genus in a close future.

Material and Methods
Measurements and counts were taken from the left side. The measurements followed Boeseman (1968) with modifications suggested by Armbruster and Page (1996), except for the folded dorsal-fin length. Furthermore, the following measurements were added: anal-fin spine length, lower caudal spine length, suborbital depth and mandibular ramus. Meristics followed Reis (2009) andSchaefer (1997). All measurements were taken point to point with digital calipers to the nearest 0.1 mm. All samples analyzed are deposited at the LBP -Laboratório de Biologia e Genética de Peixes, São Paulo State, Brazil; and MZUSP -Museu de Zoologia da Universidade de São Paulo, São Paulo State, Brazil. Abbreviations used throughout the text followed Carvalho and Reis (2009). One specimen of the new species was cleaned and doublestained (c&s) according to the method of Taylor and Van Dyke (1985).
Description. Morphometric and meristic data shown in Table 1. Small size Loricariidae, holotype 27.3 mm SL; paratypes 20.7−27.3 mm SL. Dorsal profile in lateral view straight from snout tip to anterior portion of parieto-supraoccipital, slightly convex to dorsal-fin origin. Dorsal-fin base straight, slightly concave and descending from posterior end of dorsal-fin base to caudal peduncle. Ventral profile in lateral view slightly concave from snout tip to anal-fin origin, slightly convex from analfin base to caudal-fin origin. In dorsal view body progressively narrowing posteriorly from cleithrum to caudal peduncle and anteriorly to snout tip. Greatest body depth at dorsal-fin origin. Cross-section of body between pectoral and pelvic fins dorsally Dorsal fin ii,7; its origin slightly posterior to pelvic-fin origin; when depressed reaching beyond vertical line through anal-fin insertion. Tip of branched dorsal-fin rays reaching vertical line slightly posterior of anal-fin origin. Dorsal-fin spinelet Vshaped, laterally extended; dorsal-fin locking mechanism functional. Pectoral fin i,6; tip of longest pectoral-fin ray almost reaching vertical line through center of horizontal pelvic-fin length when depressed. Pectoral axial slit present between pectoral-fin base Top of head in parieto-supraoccipital region and between orbits convex; superior margin of orbits elevated. Eyes moderately small (9.7−17.0% of HL), and dorsolaterally positioned. Snout pointed and rounded in dorsal view. Nostril small. Body and almost all head plates covered with minute, uniformly sized and evenly distributed odontodes. Absence of tufts of hypertrophied odontodes at posterior medial portion of parieto-supraoccipital or crests on head. Dorsal and ventral anterior margin of snout covered with larger odontodes compared to rest of head. Lips moderately developed and rounded; lower lip far from reaching pectoral girdle. Papillae uniformly distributed on base of dentary and premaxilla, getting smaller distally. Lower lip larger than  and lateral process of cleithrum. Lateral margin of pectoral spine possessing odontodes increasing in size posteriorly. Pelvic fin i,5; tip not exceeding anal-fin origin when depressed. Males with flap along dorsal margin of unbranched pelvic-fin ray, absent in females. Anal fin i,5; tip of unbranched anal-fin ray reaching 7th to 9th plate from anal-fin origin. Adipose-fin absent but with small unpaired plates in typical adipose fin region. Caudal fin i,14,i; distal margin forked. Lateral plate series formed by 24-26 (mode 25) plates. Lateral line with one or two unperforated plates in line of pores along mid length of body, terminating in two plates preceding last lateral plate. Abdomen completely covered by dermal plates. Cleithrum partly enclosed by ventral lamina of coracoids.
Color in alcohol. Background color dark yellowish-brown in dorsal portion of body and yellowish tan in ventral portion. Dorsal surface of head dark brownish, except for striking V-shaped yellowish tan mark from rostral plate passing through nares to orbital margins. Irregular and conspicuous dark brownish longitudinal stripe along lateral line. Four dark brownish bars crossing dorsum, reaching longitudinal stripe on sides of trunk: first below dorsal-fin origin, second at end of dorsal-fin base, third at adipose fin region, and fourth more inconspicuous at end of caudal peduncle. Dorsal, pectoral, and pelvic fins with dark chromatophores, forming irregular sets of bands: five on dorsal and pectoral fins, three to four on pelvic-fin, and four on anal fin. Dorsal-fin with triangular dark blotch at anterior base. Unpaired plates in typical adiposefin region yellowish tan. Caudal-fin hyaline, except for one black spot at its origin extending to ventral lobe, and two almost inconspicuous bands. Entire body covered with irregularly distributed chromatophores.
Sexual dimorphism. Adult males can be distinguished from females by presenting two characters: (1) presence of a papilla at urogenital opening (vs. papilla absent in females), and (2) unbranched pelvic-fin ray supporting a dermal flap on proximal dorsal surface (vs. dermal flap absent in females).
Distribution. The new species is known from three drainages of rio Tapajós in Mato Grosso State, Brazil (Fig. 4). Two from the rio Teles Pires, in the municipality of Paranaíta and from a small tributary of rio Peixoto de Azevedo, in the municipality of Peixoto de Azevedo.
Etymology. The specific name "dani" is in honor of Daniela Fernandes Roxo, FF Roxo's sister.
Discussion. Lehmann et al. (2014Lehmann et al. ( , 2015 proposed that the species P. amazonensis, P. britskii, P. collinsae, P. eppleyi, P. halbothi, P. longirostris, P. polyochrus, and P. variola should be part of a new genus of Otothyrini based on the following synapomorphies (1) presence of a triangular dark blotch at the anterior base of the dorsal fin, (2) canal cheek plate on the ventral surface of the head elongated posteriorly and contacting the cleithrum, and (3) head and snout elongated and with a Y-shaped, white or cream colored mark dorsally. The first character is apparently conserved and may help to diagnose a new genus within Otothyrini. However, it is also present in P. bidentatus (see the holotype picture in Gauger and Buckup 2005, Fig. 5). The second character is absent in P. dani and the third character is present not only in P. dani and species of this possible new genus proposed by Lehmann et al. (2014Lehmann et al. ( , 2015, but also in species of Hisonotus -e.g., H. acuen and H. chromodontus, species of Curculionichthys -e.g., C. luteofrenatus, C. paresi, and species of Epactionotus -e.g., E. bilineatus, E. itaimbezinho and E. gracilis. Given the above information, it is clear that new analyses are necessary to recognize this putative new genus more accurately. Carvalho and Datovo (2012) described a new Otothyrini species, Hisonotus bockmanni, from small tributaries of the rio Teles Pires, drainages of the rio Tapajós. This species lacks an adipose fin as the new species P. dani, and presents several small platelets at typical adipose-fin region. Furthermore, H. bockmanni shows a triangular dark blotch at the anterior base of the dorsal-fin suggesting that this species may also be part of the new genus proposed by Lehmann et al. (2014Lehmann et al. ( , 2015. However, we could not examine the clear and stained specimens of H. bockmanni to verify if this species presents the first character proposed by Lehmann et al. (2014Lehmann et al. ( , 2015, i.e., a canal cheek plate on the ventral surface of the head elongated posteriorly and contacting the cleithrum. Hisonotus bockmanni and the new species P. dani could be part of the same monophyletic genus and may be closely related. Notwithstanding, H. bockmanni can be distinguished from its congeners by the presence of the following characters of coloration pattern proposed by Carvalho and Datovo (2012): (1) the snout with unpigmented, rostrocaudally elongate ellipse anterior to each naris; (2) the dark-brown pigmented pre-dorsal region with five unpigmented white spots arranged as an anteriorly chevron-shaped blotch with three spots anteriorly of dorsal-fin and two posterior spots lateral to and coequal with insertion of dorsal-fin spine; and (3) the caudal-fin lacking pigments on half of membrane and rays.