A new species of Neotropical freshwater stingray of the genus Potamotrygon Garman , 1877 from the Río Madrede Díos , Peru ( Chondrichthyes : Potamotrygonidae )

Potamotrygon tatianae sp. nov., is described from Río Madre de Díos, Peru, upper Rio Madeira basin. The new species is distinguished from all congeners by a unique combination of characters, including its dorsal color pattern formed by a relatively slender, highly convoluted, beige to dark brown vermicular pattern, a single row of dorsal tail spines, and a relatively longer tail posterior to caudal stings. Potamotrygon tatianae sp. nov., occurs sympatrically with other species of Potamotrygon (P. falkneri, P. orbignyi and P. motoro). From the similar species P. falkneri, P. tatianae sp. nov., is further distinguished by the absence of circular, reniform, and oval spots, by its proportionally much longer tail, by having dorsal tail spines in one irregular row, and by features of the ventral lateral-line canal, dermal denticles and neurocranium. From P. orbignyi, the new species is distinct by lacking a reticulate pattern on dorsal disc and by the presence of two angular cartilages. From P. motoro, P. tatianae sp. nov., is further separated by the lack of ocelli formed by strong black concentric rings, by the more flattened aspect of its head and disc, and by having smaller and more numerous teeth. The discovery of a new species that so closely resembles a congeneric form in color pattern, a feature highly variable within the latter, highlights the importance of examining large series of individuals and of detailed morphological analyses in revealing the potentially highly cryptic nature of the diversity within the family. Key-Words: Potamotrygon tatianae sp. nov.; Potamotrygon falkneri; Taxonomy; Morphology; Cryptic species; Río Madeira; South America.

The present paper describes and compares with congeners a new species of Potamotrygon from Río Madre de Díos, Peru.This species was discovered during the preparation of a taxonomic revision of Potamotrygon falkneri Castex & Maciel, 1963, in which it was presented as Potamotrygon sp.(Silva & Carvalho, 2011).However, after a thorough morphological analysis of this form (more in-depth than in Silva & Carvalho, 2011), and a re-examination of material of Potamotrygon falkneri, it became evident that Potamotrygon sp.represents a new species, described here as Potamotrygon tatianae sp.nov.Although this new species has a color pattern that resembles P. falkneri, and overlaps in many morphological characters, it represents the only group of specimens that could not be placed among the limits of variation found within P. falkneri.Characters that separate the new species from P. falkneri were found in its distinct dermal denticles, ventral lateral-line canal system, neurocranial morphology, proportions of its tail, and conspicuous color pattern.The discovery of this new species demonstrates that much of the diversity within the family may be highly cryptic, requiring the examination of large series of specimens.

MATERIAL AND METHODS
Measurements of specimens were modified from Bigelow & Schroeder (1953) and Rosa (1985), and are listed and further described in Carvalho & Lovejoy (2011) and Silva & Carvalho (2011).Measurements were transformed into percentages of disc width (% DW) to allow direct comparisons.
Material examined is from Academy of Natural Sciences of Philadelphia, Philadelphia (ANSP), Field Museum of Natural History, Chicago (FMNH); Natural History Museum of Los Angeles County, Los Angeles (LACM); Museu de Zoologia da Universidade de São Paulo, São Paulo (MZUSP); and Museum of Zoology, University of Michigan, Ann Arbor (UMMZ).Abbreviations used throughout the text include DL for disc length, DW for disc width and TL for total length.

Diagnosis
A species of Potamotrygon distinguished from congeners by the following unique combination of characters: dorsal disc with dark background, with a beige or light brown, closely packed and highly convoluted vermicular pattern; a single row of irregular  spines on dorsal tail midline; and presence of starshaped, asymmetrical and minute dermal denticles, rarely with crown dichotomies, and concentrated over central region of disc.In relation to species of Potamotrygon in the upper Río Madeira basin, P. tatianae sp.nov., is further distinguished from P. motoro (Müller & Henle, 1841) by lacking on disc ocelli formed by strong black concentric rings, by the more flattened aspect of its disc, by presenting much smaller dermal denticles, and considerably smaller eyes.From P. orbignyi (Castelnau, 1855), P. tatianae sp.nov., is further distinguished by lacking a dorsal reticulate pattern, presence of two angular cartilages, and lower number of total pectoral radials (modal values 97 vs. 90, respectively).Potamotrygon tatianae sp.nov., is distinguished from P. falkneri by having tail spines in one irregular row (instead of in one to three irregular rows), lower total pectoral radial count (90-93 vs. 94-100, respectively), by presenting a proportionally much longer tail (mean values 109% vs. 93.5% of DW, respectively), by presenting teeth with no prominent cusps in adult males (males usually with prominent cusps in P. falkneri), and by presenting spots on dorsal disc that are exclusively vermicular, not occurring as independent spots (many specimens with individual spots on background, these mostly circular, reniform, or oval, with diameter equal to or smaller than eye in P. falkneri).

Description
Morphometric and meristic data are presented in Tables 1 and 2. Anterior portion of disc with small, prominent, and oval shaped eyes (Figure 6).Spiracles oval and small (two to three times eye diameter) situated posterior to orbits and projecting obliquely from midline.Interspiracular distance approximately 1.6 times greater than interorbital distance.Nasal curtain partially covering mouth and presenting small, fringed posterior margin (Figure 6).Mouth small (mouth width ranging from 7.8 to 11% DW); mouth opening relatively straight across, and with five buccal papillae, two lateral and three central.One of three central papillae closer to lower jaw tooth plate.Mouth width and internarial space about equal.Labial ridges present.Teeth set in quincunx, with narrow and arched upper tooth plate, and wide and trapezoidal lower tooth plate.Tooth rows varying from 36-46 on upper jaw and 33-45 on lower jaw.Teeth relatively small, wider than long, and with flattened, elliptical, or lozengeshaped crowns.Cusps rounded in males, or absent.Tooth plates presenting dignathic heterodonty.Teeth in lateral rows with elliptical crowns and generally lacking cusps.Teeth in central rows more robust, with lozenge-shaped crowns and rounded cusps; sexual dimorphism not present.Roots bilobed (holaulacorhize), with lobes separated by a shallow basal median groove.
Branchial basket relatively narrow and short, with space between first branchial slits from 22.7 to 28.2% of DW, and distance between first and last branchial slits from 15.8 to 19% of DW.Pelvic fins wider than long, partially covered by disc, and with posterior margins exposed posterior to disc margins.Clasper dorsoventrally depressed (Figure 7A), wider at bases and narrowing toward tips.Clasper groove beginning proximally at level of posterior margin of pelvics.Anterior half of clasper groove running obliquely from inner margin to outer margin of clasper.Posterior half of clasper groove curving inward at level of dorsal pseudosiphon, reaching midline and extending to clasper tip.Dorsal pseudosiphon well developed near inner edge, elliptical, and obliquely oriented in relation to midline.Ventral pseudosiphon also well developed, located at lateral distal edge of clasper.
Tail elongated (mean tail length 109% of DW) and wide (mean width 15.5% of DW), with proximal portion slightly depressed dorsoventrally, and tapering from base to just posterior to caudal sting insertion.Distal portion of tail, posterior to sting base, laterally compressed and presenting membranous dorsal and ventral caudal folds (these about 3 mm in height).Dorsal caudal fold originating underneath sting tip and extending to tail extremity.Ventral caudal fold originating at level ventral to sting base, extending to tail extremity.One irregular row of spines on middorsal tail extending from base of tail to level of sting origin.Enlarged spines on tail with rounded bases.5).Spots beige, light beige or dark brown.Some specimens presenting irregular vermicular spots forming strong vermicular patterns (Figure 4).Spots on central region narrower than the ones positioned marginally.
In addition, small circular spots on disc edges present in most specimens.Pelvic fins dorsally similar to disc.Dorsal tail also with same basic color pattern.Ventral medial region of disc white in majority of specimens.In some cases, within white background, small, rounded grey spots occur laterally and posterolaterally to gill slits.These spots scattered anteriorly, and coalesce posterioly.In some specimens, rounded and scattered gray spots also occur within the space between branchial slits.Border of disc margins gray, from level of nasal slits to posterior region of disc.Some specimens predominantly gray ventrally, with white embracing only a small portion of anterior region.In these specimens, branchial slits surrounded by gray coloration.Light gray and white circular spots may occur over gray background.Closely packed spots form continuous stripes on lateral borders of disc.In region posterior to branchial slits, a black oval spot of varying shape and intensity occurs.Pelvic fins with predominantly white ventral coloration.Dark gray coloration restricted to fine bands on posterior region of fins, presenting small circular light gray spots.Ventral tail region with white circular and sometimes vermicular spots restricted to tail borders, over a light gray background.At ventral midtail, gray background coloration homogeneous and without spots.Sensory canal system: Characteristics of ventral lateral-line canals in Potamotrygon tatianae consist of: suborbital loop originated from the infraorbital canal, close to hyomandibular canal anteriorly, and with prominent extension projecting towards middle portion of disc; numerous anterior subpleural tubules projecting from hyomandibular canal on anteriormost part of the disc; hyomandibular canal presenting a distinct undulation towards disc margin after anterior subpleural tubules; hyomandibular jugular component notoriously undulated at level of first three branchial slits; jugular canal presents a marked undulation adjacent to branchial slits; hyomandibular subpleural component presents a marked and wide undulation at level of branchial slits; mandibular canal short, obliquely oriented and with two marked undulations on its proximal portion; infraorbital loop with weak undulations at its internal corners; orbitonasal component of supraorbital canal highly undulated; final ascendant part of suborbital component highly undulated; prenasal loop short and straight; posterior subpleural tubule usually single and projecting obliquely from subpleural loop to posterolateral margin of disc.Subpleural loop also more extended posteriorly (after anterior margins of pelvic fins) (Figure 9).
Neurocranium: Neurocranium longer than wide, with elliptic and ventrolaterally expanded nasal capsules (Figure 10).Preorbital processes short and curved backwards.Postorbital processes wide, shelflike and anterolaterally expanded.Claspers: Dorsal terminal 2 long, narrow and ovalshaped with a marked groove present along its proximal portion (Figures 7B-C).Dorsal marginal trapezoidal and with a notorious groove along its axis.Accessory terminal elongated and fusiform, underlying dorsal terminal 2. Ventral terminal broad, long and oval.Ventral marginal long and narrow, with pointed anterior tip.Axial cartilage) straight, depressed anterioly and distally cylindrical, tapering toward extremity.First basal segment connecting to basipterygium and second basal segment linked to proximal part of axial cartilage.Beta cartilage originating at first basal segment and distally articulated with dorsal marginal.

Etymology
This new species honors Tatiana Raso de Moraes Possato, a late student of biology that was an enthusiastic researcher of chondrichthyans, in particular potamotrygonids.

Remarks
All specimens of P. tatianae including the type specimens, had their stings removed upon capture; consequently, morphometric data from this structure could not be analyzed.Potamotrygon tatianae has been erroneously identified as Potamotrygon castexi in systematic collections.This mistaken identification was due to similarities in dorsal disc color (vermiculate pattern), which figured as an important character in the original description of P. castexi by Castello & Yagolkowski (1969).However, a recent systematic revision of P. falkneri, based on large series of specimens including material similar to the holotype of P. castexi and from close to its type-locality, confirmed that this species is a junior synonym of P. falkneri, which is highly variable in coloration (Silva & Carvalho, 2011).Potamotrygon tatianae was previously presented, and provisionally separated, from P. falkneri in that same taxonomic work (as Potamotrygon sp.).This species is described here after a more in-depth study of its morphology.

DISCUSSION
Potamotrygon tatianae was briefly, but only tentatively presented as distinct in a recent taxonomic revision of P. falkneri (Silva & Carvalho, 2011), but the acquisition of new morphological data, concerning dermal denticle morphology, ventral lateral-line system, and skeletal anatomy, further corroborated that it represents a separate species.Although occurring sympatrically with P. falkneri in Río Madre de Díos, and P. falkneri is a species with a demonstrably high intraspecific variation in color pattern, we were able to conclude that P. tatianae does not represent an example of this variation because it can be distinguished by other internal and external morphological features.Potamotrygon tatianae was compared to all valid species of Potamotrygon, including species presently being described.Our comparisons, however, are restricted here to sympatric species, with special attention given to P. falkneri.Silva & Carvalho (2011) presented a series of external morphological characters, in addition to morphometric and meristic data, which separated P. tatianae from P. falkneri.These characters are expanded here, with the inclusion of further features from internal anatomy.Potamotygon tatianae can be distinguished from P. falkneri by the following external characters: presence of a single row of spines over dorsal tail, not nearly as irregularly arranged (vs.one to three highly irregular rows in P. falkneri); dermal denticles rarely presenting crown dichotomies and with flattened, wide and pointed, highly protruded crown plates (vs.high number crown dichotomies and rounded, small-sized crown plates in P. falkneri); teeth with rounded cusps in males, with males and females presenting equal-sized, morphologically similar teeth (vs.some males bearing triangular prominent cusps in P. falkneri); tail homogeneously gray on its central, ventral portion, with irregular white spots scattered laterally (vs.disorganized reticulated pattern on tail, formed by irregular vermicular white spots in P. falkneri); coloration on dorsal disc exclusively composed of slender, closely packed vermiculations (vs.reniform, and oval spots on background with diameter equal to or smaller than eye diameter in P. falkneri) (Figure 13).A meristic feature that also supports P. tatianae as a distinct species is the slightly lower number of total pectoral radials (modal values 90 vs. 97, respectively).Potamotrygon tatianae has a considerably longer tail region posterior to sting insertion (mean 109% of DW, n = 7), compared to P. falkneri from Paraná-Paraguay and upper Amazon basins (mean 87.9% DW, n = 65 and mean 93.5% DW, n = 10, respectively).This greater tail extension is not related to the number of total vertebrae, but is associated to the presence of a longer cartilaginous rod which supports the distal part of tail posterior to last vertebral centrum (individual centra do not occur posterior to caudal stings).For some measurements, P. tatianae has higher proportional values compared with P. falkneri from upper Amazon and Paraná-Paraguay basins: snout to cloaca (mean 92.4% DW, n = 7 vs. mean 89.2% DW, n = 10 and mean 87.3% DW, n = 65, respectively), pelvic fin width (mean 62.2% DW, n = 7 vs. mean 58.1% DW, n = 10 and mean 57% DW, n = 65, respectively), and branchial basket length (mean 17.1% DW, n = 7 vs. mean 15.1 % DW, n = 10 and mean 15.7% DW, n = 65, respectively).
The ventral lateral-line canal system (Figure 9) differs between P. tatianae and P. falkneri in the following characters: the hyomandibular canal presents in P. tatianae a distinctive undulation towards outer disc margin just before the beginning of anterior subpleural tubules (absent in P. falkneri); hyomandibular subpleural component with a marked and wide undulation in P. tatianae at level of branchial slits (devoid of any evident undulation in P. falkneri; orbitonasal component of supraorbital canal highly undulated in P. tatianae (rather homogeneous in P. falkneri); and subpleural loop also more extended posteriorly, surpassing the limits of anterior margins of pelvic fins in P. tatianae (not extended posteriorly in P. falkneri).
In relation to the neurocranium (Figure 10), P. tatianae has the anterior cerebral vein foramen farther from the optic nerve foramen and closer to posterior foramen for preorbital canal when compared with P. falkneri (three specimens of P. falkneri examined, one of P. tatianae).Additionally, in P. tatianae, the efferent spiracular artery foramen is not closely positioned to the optic nerve foramen and eye stalk as it is in P. falkneri, but is more ventrally situated, closer to neurocranial shelf.
Potamotrygon tatianae is further distinguished from P. orbignyi (more information on this species is provided in Silva, 2010) by the absence of a strong reticulate dorsal pattern that forms hexagonal figures (that are sometimes interrupted) on dorsal disc, presence of two angular cartilages (a single, long anterior angular cartilage in P. orbignyi), teeth with rounded cusps (teeth with three pointed cusps in P. orbignyi), slight higher number of total pectoral radials (modal 90 vs. 97 in P. orbignyi), suborbital loop close to the hyomandibular canal anteriorly (suborbital loop far from hyomandibular canal anteriorly in P. orbignyi), neurocranium highly calcified and with preorbital process not much developed (neurocranium less calcified and with well developed, lateroposteriorly extended preorbital process in P. orbignyi), and considerably wider (mean 15.5% DW vs. 11.7%DW in P. orbignyi) and longer (mean 109.0%DW vs. 92.0%DW in P. orbignyi) tail region.
The discovery of a new species so similar to a pre-existing, valid species that is widely distributed (P.falkneri), and which is demonstrably highly variable in color pattern (and in a few other characters as well, such as in number of dorsal tail spine rows), highlights that much cryptic diversity may exist in the family.Such cryptic diversity can only be brought to light through the examination of large, well represented series of specimens.This discovery also highlights the continual importance of morphology in uncovering such cryptic diversity, as dissections and close inspection of the ventral lateral-line canals, dermal denticles and neurocrania were of paramount importance in separating P. tatianae from P. falkneri.
Manuscripts are considered on the understanding that they have not been published or will not appear elsewhere in substantially the same or abbreviated form.The criteria for acceptance of articles are: quality and relevance of research, clarity of text, and compliance with the guidelines for manuscript preparation.
Manuscripts should be written preferentially in English, but texts in Portuguese or Spanish will also be considered.Studies with a broad coverage are encouraged to be submitted in English.All manuscripts should include an abstract and keywords in English and a second abstract and keywords in Portuguese or Spanish.
Authors are requested to pay attention to the instructions concerning the preparation of the manuscripts.Close adherence to the guidelines will expedite processing of the manuscript.
Manuscript Form: Manuscripts should not exceed 150 pages of double-spaced, justified text, with size 12 and source Times New Roman (except for symbols).Page format should be A4 (21 by 29.7 cm), with 3 cm of margins.The pages of the manuscript should be numbered consecutively.Institution(s).The title should be concise and, where appropriate, should include mention of families and/or higher taxa.Names of new taxa should not be included in titles.
(5) References: The literature cited should be arranged strictly alphabetically and given in the following format: • Journal Article: Author(s).Year.Article title.Journal name, volume: initial pagefinal page.Names of journals must be spelled out in full.
Tables: All tables must be numbered in the same sequence in which they appear in text.
Authors are encouraged to indicate where the tables should be placed in the text.They should be comprehensible without reference to the text.Tables should be formatted with vertical (portrait), not horizontal (landscape), rules.In the text, tables should be referred as Table 1, Tables 2 and 4, Tables 2-6.Use "  Responsability: Scientific content and opinions expressed in this publication are sole responsibility of the respective authors.
Copyrights: The journals Papéis Avulsos de Zoologia and Arquivos de Zoologia are licensed under a Creative Commons Licence (http://creativecommons.org).
For other details of manuscript preparation of format, consult the CBE Style Manual, available from the Council of Science Editors (www.councilscienceeditors.org/publications/style).
Papéis Avulsos de Zoologia and Arquivos de Zoologia are publications of the Museu de Zoologia da Universidade de São Paulo (www.mz.usp.br).
Always consult the Instructions to Authors printed in the last issue or in the electronic home pages: www.scielo.br/pazor www.mz.usp.br/publicacoes.
External morphology: Disc oval, longer than wide (DL varying from 102.6 to 131.2% of DW) (Figures 1-5).Anterior margin of disc convex, with a small fleshy protuberance on snout.Posterior margins of disc also convex.Disc dorsoventrally compressed.

Dermal denticles :
Disc with scattered dermal denticles mainly on midregion, from interorbital area to tail base (Figure8).Denticles on middisc with predominantly four crown ridges.Crown ridges rarely showing crown dichotomies.In dorsal view, denticles asymmetrical and star-shaped due to different lengths of crown ridges.Denticles in central region with wide and flattened crown plates, bearing pointed projections.Anterior crowns ridges or closer to crown plate projection shorter than posterior ones.Minute dermal denticles interspersed with larger denticles, exhibiting two crown ridges.Denticles become dispersed and smaller farther away from central disc region, with crown ridges becoming less evident.Denticles on disc margins practically absent.Dermal denticles also occur around and on margins of spiracle openings, as well as on orbits.Denticles devoid of crown ridges, but with pointed crowns, occur exclusively on spiracle superior margins, whereas denticles with two crown ridges occur on remaining regions.Pelvic fins and claspers devoid of dermal denticles.Denticles on dorsal tail small, devoid of crown ridges and with crowns sharply pointed.Dorsal caudal fold presenting numerous very small dermal denticles; ventral caudal fold devoid of dermal denticles.Dermal denticles also occur on lateral tail region, from slightly anterior to sting base to distal tail extremity.Denticles more developed near base of caudal stings.Coloration: Disc background color generally blackish-brown.Spots on background close together, narrow, with variable extensions and presenting exclusively vermicular shapes (Figures 1-

FIGURE 12 :
FIGURE 12: Map showing geographic distribution of Potamotrygon tatianae sp.nov.Star indicates collection locality of specimens and all of type-species.
The text should be arranged in the following order: Title Page, Abstracts with Keywords, Body of Text, Literature Cited, Tables, Appendices, and Figure Captions.Each of these sections should begin on a new page.(1) Title Page: This should include the Title, Short Title, Author(s) Name(s) and

Illustrations:
Figures should be numbered consecutively, in the same sequence that they appear in the text.Each illustration of a composite figure should be identified by capital letters and referred in the text as: Fig. 1A, Fig. 1B, for example.When possible, letters should be placed in the left lower corner of each illustration of a composite figure.Handwritten lettering on illustrations is unacceptable.Figures should be mounted in order to minimize blank areas between each illustration.Black and white or color photographs should be digitized in high resolution (300 DPI at least).Use "Fig(s)."for referring to figures in the text, but "FIGURE(S)" in the figure captions and "fig(s)."when referring to figures in another paper.

)
Abstract: All papers should have an abstract in English and another in Portuguese or Spanish.The abstract is of great importance as it may be reproduced elsewhere.It should be in a form intelligible if published alone and should summarize the main facts, ideas, and conclusions of the article.Telegraphic abstracts are strongly discouraged.Include all new taxonomic names for referencing purposes.Abbreviations should be avoided.It should not include references.Abstracts and keywords should not exceed 350 and 5 words, respectively.Primary headings in the text should be in capital letters, in bold and centered.Secondary headings should be in capital and lower case letters, in bold and centered.Tertiary headings should be in capital and lower case letters, in bold and indented at left.In all the cases the text should begin in the following line.
(3) Body of Text: The main body of the text should include the following sections: Introduction, Material and Methods, Results, Discussion, Conclusion, Acknowledgments, and References at end.
TABLE" in the table heading.