A new species of Aphanotorulus ( Siluriformes : Loricariidae ) from the rio Aripuanã basin , Brazil

The cis-Andean genus Aphanotorulus was recently revised and comprises six valid species: A. ammophilus, A. emarginatus, A. gomesi, A. horridus, A. phrixosoma and A. unicolor. Herein, a new species is described from tributaries of the rio Aripuanã basin, in Amazonas and Mato Grosso states, Brazil. The new species is easily distinguished from congeners by its color pattern: caudal fin with upper lobe mostly hyaline with dark spots along rays and membranes, and lower lobe red and without dark spots; and absence of dark spots in the lateral series of mid-ventral plates.


Introduction
The genus Aphanotorulus Isbrücker & Nijssen, 1983 is distinguished from most hypostomines by an elongate body with a cream-colored background completely covered by round or elongate dark spots.Aphanotorulus includes medium to large size species that vary from 150 mm to 500 mm in total length, and have a moderately depressed body, ventrally flat caudal peduncle, and large fins.The caudal fin is particularly large and, in some species, strongly forked.Representatives of this genus, formerly known as the Hypostomus emarginatus group, have a convoluted taxonomic history during which a variety of nomenclatural arrangements have been proposed (see Ray, Armbruster, 2016 for a brief review).
Aphanotorulus was originally distinguished from the genus Hypostomus by the presence of numerous buccal papillae on the oral cavity (vs. a single papillae); short body up to 150 mm SL (vs.usually > 150 mm SL in almost all Hypostomus); elongate hypobranchials (vs.short and stocky); and sex-related hypertrophied odontodes over the entire body surface (vs.sexual dimorphism not involving the elongation of odontodes over the entire body) (Armbruster, Page, 1996).

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In 2004, Armbruster in a morphology-based cladistic analysis of Hypostominae including Aphanotorulus ammophilus Armbruster & Page, 1996, A. unicolor (Steindachner, 1908), Hypostomus emarginatus (1 and 2), H. squalinus and Isorineloricaria spinosissima, observed the paraphyly of this group inserted inside a large Hypostomus clade.Lujan et al. (2015), in a molecular phylogeny using both Bayesian Inference and Maximum Likelihood methods, erected a new division for the tribe Hypostomini: Hypostomus continued to be monophyletic with exclusion of the species in the Hypostomus emarginatus group: Aphanotorulus ammophilus, A. emarginatus n. comb., A. squalinus n. comb.and Isorineloricaria spinosissima.All analyzed members of the Hypostomus emarginatus group emerged as being more closely related to members of the Peckoltia Clade (Bayesian posterior probability, BPP = 1, Maximum likelihood bootstrap, MLB = 95) than of the Hypostomini Clade.Support for this analysis was strong for Aphanotorulus (BPP = 1, MLB = 99); however, support for the monophyly of Aphanotorulus emarginatus and A. squalinus in the analysis was weak.Therefore, based on molecular analysis, Lujan et al. (2015) recognized the species of Squaliforma in Aphanotorulus.
For this new arrangement, Ray, Armbruster (op cit.), proposed that Aphanotorulus be distinguished from Isorineloricaria by a caudal peduncle oval in cross section and not greatly elongated (vs.caudal peduncle round in cross-section and proportionately longer), and by the presence of small dark spots (less than half lateral plate diameter) on a light tan background (vs.spots almost as large as lateral plates on a nearly white background).Here, based on recently collected material, we describe a new species of Aphanotorulus from the rio Aripuanã basin.

Material and Methods
Measurements and counts follow Boeseman (1968), modified from Weber (1985) and Zawadzki et al. (2008); the latter authors added the width and length of the lower lip.Measures were taken from the left side of the body, whenever possible.Plate counts and nomenclature follow Schaefer (1997) and Oyakawa et al. (2005)

Figs. 1-2
Hypostomus emarginatus.-Pedroza et al., 2012: 13 [species     Diagnosis.Aphanotorulus rubrocauda can be distinguished from all other species of Aphanotorulus by its color pattern: having a uniformly red colored lower caudal-fin lobe (vs.lower lobe of caudal fin with dark spots on creamy colored background), by the absence of dark spots on the posterior half of mid-ventral lateral plate series (vs.presence of dark spots in all lateral plate series).Additionally, Aphanotorulus rubrocauda is distinguished from congeners by having more premaxillary teeth (32-65 per ramus, mean = 45; vs. 15-34, mean = 24) and dentary teeth (30-63 per ramus, mean = 44; vs. 14-34, mean = 25).Aphanotorulus rubrocauda further differs from A. emarginatus by having small round dark spots (vs.dark large and elongated spots) (Fig. 3).Dorsal fin II,7, branched rays decreasing in length posteriorly.Last branched ray 2/3 shorter than dorsal-fin spine.Pectoral fin I,6; distal tip of branched rays surpassing insertion of pelvic fin; pectoral-fin spine slightly curved inward and depressed, distal region with hypertrophied odontodes along laterodorsal surface in larger specimens.Pelvic fin i,5, distal tip of branched rays reaching insertion of anal-fin.Pelvic fin unbranched ray slightly curved inward and rounded with thin extremity.Forked caudal fin i,14,i.Unbranched ray of lower lobe slightly longer than that from upper lobe.All rays with small odontodes.Caudal fin with seven branched rays in each lobe.Anal-fin branched rays of coequal length.

Coloration in alcohol.
Body with light brown base color covered with rounded dark spots; spots slightly smaller and more densely organized on head than on trunk and fins.Distal portion of pectoral and pelvic fins hyaline and without dark spots.Dorsal-fin spine with 16-17 spots, inter radial membranes with 10-11 spots each; branched rays uniformly colored.Spots on pectoral fin arranged from insertion to distal end of all fin rays.Pelvic fin with spots from insertion to distal third; plain or hyaline along margin.Presence of dark spots on lateral series of plates, except on mid-ventral and ventral series.Upper lobe of caudal fin cream colored with dark spots on simple and branched rays; lower lobe lacking spots, uniformly reddish to brown.Red coloration on lower caudal fin lobe restricted to branched rays; unbranched ray almost uniform.Dark spots on body and fins becoming more numerous in adults (Figs.1-2).
Coloration in life.Similar to preserved specimens, but more intensely red on lower lobe of caudal fin.In juveniles (up to 110.0 mm SL) both lobes are red, with a few dark spots on base of upper lobe.In adults only the lower lobe is red, whereas the upper lobe has more sparsely distributed spots for its entire extension (Fig. 2).
Geographical distribution and ecological notes.The new species was found in fast-running waters of tributaries of the rio Aripuanã basin, a right bank tributary of the rio Madeira that stretches from the Mato Grosso to Amazonas States (Fig. 4).The rio Aripuanã is a dark-colored water river, poor in sediments, having cataracts, large boulders and a rocky bottom from its middle reach upward, stretching approximately 800 km from its headwaters until its confluence with the sediment-loaded rio Madeira.The rio Aripuanã receives many clear-water, rocky-bottom tributaries that drain the Brazilian Shield.
Etymology.The specific epithet, rubrocauda, is from the Latin rubro, meaning red, and cauda referring to caudal fin.

Discussion
The new species has a distinct coloration from all congeners.In Aphanotorulus ammophilus, A. emarginatus, A. gomesi, A. horridus, A. phrixosoma, and A. unicolor the lower and upper lobe of the caudal fin are completely covered with several series of transversely aligned conspicuous dark spots on the membrane and on the rays (Fig. 5).Other characteristic that distinguishes A. rubrocauda from the others species of Aphanotorulus is the absence of dark spots on the pelvic fin, although these are present in some specimens.Aphanotorulus rubrocauda also differs from its congeners by inhabiting a different type of environment.Whereas most Aphanotorulus species inhabit sandy beaches that are periodically formed on the margin or shores of the central channel of the white-water rivers, A. rubrocauda inhabits streams of clear to lightly-sediment loaded waters, with rapids with rocks and sandy substrate (Fig. 6).Aphanotorulus rubrocauda is currently only recorded from tributaries of the rio Aripuanã basin, mainly the rio Guariba, rio Madeirinha and rio Roosevelt.These rivers are inserted in a mosaic of Conservation Units of Amazonas State, Brazil.
The rio Aripuanã basin hosts a considerable diversity of fishes, with 26 new species described in the past two decades (Kullander, 1995;Ribeiro et al., 2011, Deprá et al., 2014;Zawadzki, Holanda Carvalho, 2014;Tencatt, Ohara, 2016), which indicates the need for strong conservation measures.However, the rio Aripuanã basin is one of the several rivers in the Amazon basin targeted for construction of hydroelectric dams.In addition to Dardanelos Hydropower, which is already built in the Aripuanã Municipality, Mato Grosso State, there are ongoing governmental projects for additional dams to be constructed on the rio Aripuanã and rio Roosevelt (Fearnside, 2015).This scenario may lead to environmental modifications that put this remarkable biodiversity at risk.

Fig. 4 .
Fig. 4. Distribution of Aphanotorulus rubrocauda in the rio Aripuanã basin.Type locality is represented by the yellow circle.Some symbols represent more than one lot or locality.
Description.Morphometric and count data are given in Tab.1.Long and moderately depressed body in lateral view; body trapezoid in cross section.Dorsal profile slightly convex from snout to dorsal-fin origin, then descending almost straight to caudal-fin procurrent ray and rising again to caudal-fin origin.Ventral profile straight from snout to caudalfin origin.Median series of plates slightly carenate; midventral series not forming prominent keel.Greatest body width anterior to cleithral region.Scapular girdle and abdominal surfaces covered by small plates of uniform size.First anal-fin pterygiophore exposed, located anterior to anal-fin origin, in ventral view.Three pre-dorsal plates.Supraoccipital usually with small median ridge and bordered by three plates.Nine plates between dorsal and adipose fin.Seven plates at dorsalfin base.Median series with 28 perforated plates.Head short, depressed and triangular in dorsal view.Snout tip slightly rounded with small odontodes.Orbit slightly elevated, bordered by small odontodes; flat interorbital region.Eyes moderately large (15.1-22.1% in HL).Maxillary barbel short, cylindrical, not reaching transverse line on lower lip edge.Presence of large buccal papilla, square and wide, covered distally by multiple small papillae.Mouth wide.Upper lip rounded in ventral view and without marginal fringes.Lower lip rounded and covered with papilla, decreasing in size distally.Odontodes present on anterior surface of snout ventral edge.Morphometric data and meristics of Aphanotorulus rubrocauda, new species.