Potamotrygon tatianae Silva & Carvalho, 2011, sp. nov.
Creators: name: Da Silva, João Paulo C. B.
name: De Carvalho, Marcelo R.
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Myliobatiformes
Potamotrygonidae
Potamotrygon
Potamotrygon tatianae

description: Potamotrygon tatianae, sp. nov.
(Figures 1-12, Tables 1-2)
Potamotrygon sp: Silva & Carvalho, 2011: 209, 212, 223, 224, 227, 228, figs. 12-13 (redescription of Potamotrygon falkneri).
Holotype
MZUSP 107673 (adult male, 348 mm DW), Río Madre de Díos, municipal district of Boca Manu, upper Amazon basin, state of Madre de Dios, Peru, 12°40’S, 71°04’06”W, May 2001, coll. F.B. Reyda (Figure 1).
Paratypes
MZUSP 107667 (adult male, 362 mm DW), Río Madre de Díos, municipal district of Boca Manu, upper Amazon basin, state of Madre de Díos, Peru, 12°40’S, 71°04’06”W, May 2001, coll. F.B. Reyda (Figure 2); MZUSP 107668 (PREADULT?female, 265 mm DW), same data as MZUSP 107667 (Figure 3).
Non type material
MZUSP 107669 (adult male, 293 mm DW), Río Madre de Díos, municipal district of Boca Manu, upper Amazon basin, state of Madre de Díos, Peru, 12°40’S, 71°04’06”W, May 2001, coll. F.B. Reyda; MZUSP 107670 (adult male, 300 mm DW), same data as MZUSP 107669; MZUSP 107671 (adult male, 351 mm DW), same data as MZUSP 107669; MZUSP 107672 (preadult? male, 291 mm DW), same data as MZUSP 107669.
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.
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. 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.
Dermal denticles: Disc with scattered dermal denticles mainly on midregion, from interorbital area to tail base (Figure 8). 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 1-5). 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. Triangular supraorbital processes slightly anterior to postorbital processes. Supraorbital crests extending from region posterior to preorbital processes to postorbital processes. Condyles of antorbital cartilages on posterolateral extremities of nasal capsules. Precerebral fontanelle and frontoparietal fontanelle partially separated by a well developed epiphysial bar. Hyomandibular facet located on ventrolateral corner of otic region. Dorsally, presence of anterior foramen for preorbital canal, and several foramina for the superficial ophthalmic nerve, piercing supraorbital crest. Paired internal carotid artery foramina near ventrolateral edges of neurocranium. Laterally, neurocranium with oval eye-stalk just posterior to wide and oval optic nerve foramen. Oculomotor nerve foramen dorsal to eye-stalk. A bridge-like lateral commisure present external to hyomandibular branch of facial nerve foramen. Posterior foramen for preorbital canal located dorsally, at junction of nasal capsule and orbit. Anterior cerebral vein foramen anterior located to optic nerve foramen. Efferent spiracular artery foramen posteroventral to eye-stalk. Orbital fissure located above and slightly anterior to hyomandibular branch of facial nerve foramen. Foramen magnum circular. Articular surface and occipital condyles ventral to foramen magnum. Vagus nerve foramen positioned laterally to foramen magnum; glossopharyngeal nerve foramen located dorsolaterally to occipital condyles. Anterior endolymphatic foramen and posterior perilymphatic foramen in parietal fossa dorsally in otic region.
Hyomandibular arch: Hyomandibular cartilages elongate, wide and laterally compressed (Figure 11). Hyomandibula articulates with Meckel’s cartilage by means of robust hyomandibular-Meckelian ligament in which anterior and posterior angular cartilages are embedded; anterior angular more robust than posterior. Meckel’s cartilage and palatoquadrate flattened; antimeres of both arches not fused symphysially. Palatoquadrate slightly arched, straight at dorsal border and with pronounced curvature on proximal region of ventral margin. Robust posterior triangular projections present close to lateral edges of palatoquadrates. Meckel’s cartilages more arched than palatoquadrates, with striking curvature on dorsal margins and with a pronounced concavity on inner corners that articulate with palatoquadrates. A marked curvature present on external aspect of Meckel’s cartilage for attachment of hyomandibular-Meckelian ligament. Ventrolateral processes projecting from both extremities of Meckel’s cartilages.
Claspers: Dorsal terminal 2 long, narrow and ovalshaped with a marked groove present along its proximal portion (Figures 7 B-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.
Geographical distribution
Potamotrygon tatianae is known only from Río Madre de Díos, upper Río Madeira basin, Peru (Figure 12).
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.
description: Published as part of Da Silva, João Paulo C. B. & De Carvalho, Marcelo R., 2011, A New Species Of Neotropical Freshwater Stingray Of The Genus Potamotrygon Garman, 1877 From The Río Madre De Díos, Peru (Chondrichthyes: Potamotrygonidae), pp. 139-154 in Papéis Avulsos de Zoologia 51 (8) on pages 139-154, DOI: 10.1590/s0031-10492011000800001, http://zenodo.org/record/10085992