Plesiotrygon iwamae Rosa, Castello & Thorson, 1987

De Carvalho, Marcelo R. & Ragno, Maíra P., 2011, An Unusual, Dwarf New Species Of Neotropical Freshwater Stingray, Plesiotrygon Nana Sp. Nov., From The Upper And Mid Amazon Basin: The Second Species Of Plesiotrygon (Chondrichthyes: Potamotrygonidae), Papéis Avulsos de Zoologia 51 (7), pp. 101-138 : 101-138

Plesiotrygon iwamae Rosa, Castello & Thorson, 1987

( Figures 17-27 ; Tables 3-6)

Elipesurus strogylopterus : Miranda Ribeiro, 1959: 6 (non Schomburgk, 1843).

Potamotrygon scobina : Taniuchi, 1982: 27 (non Garman, 1913).

Plesiotrygon iwamae Rosa, Castello & Thorson, 1987: 447-458 , figures 1-10 (original description); Taniuchi & Ishihara, 1990: 14, 15 (claspers); Zorzi, 1995: 18 (historical account); Compagno & Cook, 1995: 67, 72, 73, 80 (brief account, compiled from Rosa et al., 1987); Carvalho, 1996: 1048 (cited); Lovejoy, 1996: 212, 216, 223-229, 233, 234 (morphology, relationships); Lovejoy et al., 1998: 1 (molecular phylogeny); Compagno, 1999: 495 (listed as valid); Carvalho et al., 2003: 23 (taxonomic account); Carvalho et al., 2004: 10, 61, 81, 88, 90 (morphology, relationships); Compagno, 2005: 540 (listed as valid); Schaefer & Summers, 2005: 303, 312 (listed, material examined); Lonardoni et al., 2006: 196 (cited); Rosa & Carvalho, 2007: 17 (listed as valid, Brazil); Luchetti et al., 2008: 131-133, 135, 140 (parasites); Toffoli et al., 2008: 325, 327, 332 (molecular phylogeny); Shibuya et al., 2009: 467, 471 (stomach contents); Domingues & Marques, 2010: 829, 832 (parasites); Ortega et al., 2010: 34 (listed, Peru); Rosa et al., 2010: 246, 247, 257, 260, 264 (general account on family).

Holotype

MZUSP 10153 , Rio Solimões , 03°22’S, 64°43’W, near Tefé, Amazonas, Brazil, 3 October 1981, coll. H. Britski.

Paratypes

FMNH 94500 , Río Napo, at Anangu, Napo district, Ecuador, 00°31’36”S, 76°23’12”W, 10 October 1981, coll. D. Stewart, M. Ibarra & R. Barriga ( Figures 17 , 24 ) ; MNRJ 573 , Rio Amazonas , Amazonas, Brazil, from Instituto Oswaldo Cruz (no further data) ; MZUSP 14789 , Rio Solimões , 03°25’S, 60°17’W, Amazonas, Brazil, January 1977 , R / V Alpha Helix ; USNM 258298 , Rio Solimões , Tabatinga, Amazonas, Brazil, 13 June 1969 , coll. T.B. Thorson et al.; ZMH 10343 , Rio Solimões , Amazonas, Brazil, 6 November 1909, coll. Scholz.

Non type material

MZUSP 42848 , Baía de Marajó, Tupinambá , Pará, Brazil, coll. M. Goulding ; MZUSP 59896 , Rio Solimões , 03°18’S, 67°92’W, Amazonas, Brazil, 22 November 1993, coll. J.P. Friel et al.; MZUSP 59897 (same data as MZUSP 59896) ; MZUSP 59898 , Rio Jutaí , 02°87’S, 66°93’W, Amazonas, Brazil, 16 November 1993, coll. J.G. Lundberg et al. ( Figure 18 ); MZUSP 59899 , Rio Amazonas , 03°28’S, 58°57’W, Amazonas, Brazil, 20 October 1994, coll. M. Westneat et al.; MZUSP 108706 , data as in MZUSP 108767 (below) (PA 07-21) ; MZUSP 108707 , data as in MZUSP 108767 (below) (PA 07-31) ; MZUSP 108767 , Baía de Marajó , 00°55’34”S, 48°17’25”W, Colares, Pará, Brazil, 20 August 2007, coll. F.P.L. Marques, M. Cardoso Jr. & V.M. Bueno (PA 07-23) ; MZUSP 108768 , data as in MZUSP 108767 (PA 07-24) ; MZUSP 108769 , data as in MZUSP 108767 (PA 07-27) ; MZUSP 108770 , data as in MZUSP 108767 (PA 07-28) ; MZUSP 108771 , data as in MZUSP 108767 (PA 07-29) ; MZUSP 108793 , data as in MZUSP 108767 (PA 07-30) ; MZUSP 108772 , data as in MZUSP 108767 , 21 August 2007 (PA 07-38) ; MZUSP 108773 , data as in MZUSP 108767 , 22 August 2007 (PA 07-39) ; MZUSP 108774 , data as in MZUSP 108767 , 22 August 2007 (PA 07-40) ; MZUSP 108775 , data as in MZUSP 108767 , 22 August 2007 (PA 07-47) ; MZUSP 108776 , data as in MZUSP 108767 , 22 August 2007 (PA 07-48) ; MZUSP 108790 , Baía de Marajó , 00°55’34”S, 48°17’25”W, Colares, Pará, Brazil, 16 August 2007, coll. F.P.L. Marques, M. Cardoso Jr. &

V.M. Bueno (PA 07-01) ; MZUSP 108791 , Baía de Marajó , 00°55’34”S, 48°17’25”W, Colares, Pará, Brazil, 16 August 2007, coll. F.P.L. Marques, M. Cardoso Jr. & V.M. Bueno (PA 07-08) ; MZUSP 108792 , Baía de Marajó , 00°55’34”S, 48°17’25”W, Colares, Pará, Brazil, 20 August 2007, coll. F.P.L. Marques, M. Cardoso Jr. & V.M. Bueno (PA 07-22). Plesiotrygon cf. iwamae (2 specimens) : MUSM 39977 , Río Amazonas, Loreto Department , Maynas Province , Sargento Lores District , town of Aucayo Caserio, near Tamshiyacu, Peru, 03°59’13.21”S, 73°10’02.80”W, altitude 89 m, 15 November 2010, coll. Homero Sanchez.

Diagnosis

A species of Plesiotrygon , distinct from P. nana , by presenting the following characters: dorsal disc coloration with a light gray, brown or light reddish-brown background color, with numerous white or creamy-white larger blotches (close to size of spiracles) and irregular ocelli formed by smaller spots on central and posterolateral disc, with smaller, irregular spots sometimes surrounding ocelli; disc and snout markedly oval; spiracle strongly rhomboidal, with mean spiracle length 6.8% DW; snout proportionally elongate (preorbital and preoral lengths greater or equal to one-fourth DW, respectively); nasal curtain relatively wide (mouth width and internarial distance close to 10.0% DW); dorsal tail region usually with a single irregular row of enlarged spines extending to caudal stings; adult specimens with numerous tooth rows, ranging from about 40-60/42-64; distal coloration of tail, as of caudal stings, creamy white ventrally and light gray dorsally, with creamy white distal whip; relatively low number of pectoral radials, from 77-84 with a modal count of 78 ( Table 4); relatively high caudal vertebrae ranging from 93-98, with a modal count of 94 ( Table 4); great size, upwards of 650 mm DL or DW, reaching sexual maturity only at or over 420 mm DL or DW; external hyomandibular canal of the ventral lateral-line system with undulations at midlength, where canal bulges towards outer disc; hyomandibular canal abruptly inflected toward midline at its posterior third; and internal hyomandibular canal strongly directed toward midline posterior to gill arches. For comparisons, see also diagnosis above for Plesiotrygon nana .

Description

Plesiotrygon iwamae has an oval disc, consistently longer than wide ( DL ranging from 98.6 to 104.5% DW, mean 102.3% DW; Table 3) (for description below, refer to Figures 17-21 ). Anterior disc also markedly oval, with knob-like anterior protrusion always present. Anterior disc region relatively elongate, with preorbital length varying from 25.7 to 28.9% DW (mean 27.4% DW), prenasal lengths from 18.0 to 23.2% DW (mean 19.5% DW), and preoral length ranging from 22.6 to 27.9% DW (mean 25.0% DW). Eyes very small, not protruding from head, but spiracles relatively wide, rhomboidal, much greater than reduced eyes (in measured specimens, mean length of spiracles 6.8% DW, mean eye-diameter 1.8% DW; in holotype, spiracle length 8% DW, and eye-length 1.8% DW). Nasal curtain relatively wide, wider than long, with medially notched, fringed posterior margin. Junction of prenasal and supraorbital canals forming a concealed, triangular mark on nasal curtain. Rounded, tubular narial fold present. Internarial distance from 7.6 to 10.0% DW (mean 8.7% DW). Mouth also relatively wide, from 8.1 to 13.9% DW (mean 10.9% DW; 12.9% DW in holotype). Teeth set in quincunx, very small and numerous (30-60/31-64 rows, holotype with 60/64 teeth), with greater cusps in larger males. Usually five buccal papillae present inside mouth.

Pelvic fins protruding significantly from posterior disc region, somewhat triangular in dorsoventral view, and broadest posteriorly. Pelvic fin width ranging from 45.5 to 56.4% DW (mean 50.5% DW, in holotype 53.6% DW). Clasper relatively stout and short, with rounded posterior tip. Clasper groove broadly arched from apopyle to hypopyle; dorsal pseudosiphon relatively small, positioned at a slight angle ( Figure 21). Ventral pseudosiphon situated on external margin of clasper tip, slightly concealed in dorsal view. Tail width at base about as wide as interspiracular distance, greatly variable in preserved material (ranging from 9.6 to 19.6% DW, mean 14.8% DW, in holotype 12.5% DW). Tail very long, greater than twice DL or DW, terminating far posteriorly as a filiform whip. Ventral median groove present, extending from tail base to beyond caudal stings posteriorly. Relatively tall ventral tail-fold originating within groove near level of caudal sting origin, tallest at more or less midlength of caudal stings ( Figure 19F ), and extending posteriorly for more than twice length of caudal stings. Lateral and dorsal tail folds absent. Caudal stings positioned relatively far posteriorly on dorsal tail (distance from tail base to their origin greater than one-half of disc width).

Dorsal color variable, with light gray, brown to reddish-brown background ( Figure 20 ). Numerous large (near size of spiracles), faint, creamy white or white spots or irregular ocelli present over middisc or posterolateral disc. These spots formed by smaller speckles of white, with slightly lighter interior color. Larger, irregular spots surrounded by smaller, very faint spots. Other light irregular vermicular markings sometimes present. Some specimens with more regular, circular ocelli (e.g. MZUSP 59896; Figure 19A ). Intensity of dorsal spots and ocelli vary greatly among specimens. Holotype with more uniform dark grayishbrown color, with scattered darker spots about size of eye-diameter, and smaller, white specks on outer disc. Tail base region and area of caudal stings with lateral alternating stripes of gray and creamy white. Filiform whip creamy white in color ventrally, sometimes grayish dorsally. Ventral color white to creamy white, some specimens, such as holotype, with grayish markings on posterior disc margins, pelvic fins and base of tail area. Holotype with dark filiform caudal whip.

Remarks

Plesiotrygon iwamae was already known to have a relatively broad distribution when described; the type-series includes specimens from Ecuador (Río Napo) and Brazil (Rio Solimões, as far east as near Manaus). Specimens are now known from Peru in the upper Río Amazonas (e.g. near Iquitos; Ross & Schäfer, 2000; Ortega et al., 2010), as well as from Baía de Marajó, Rio Pará, their easternmost occurrence (see material examined) – a span of more than 5000 km. Based on examination of material from its entire range, however, we can advance that although there is variation, especially in dorsal coloration ( Figure 20 ) and dorsal tail spines, consistent characters that subdivide P. iwamae into more than one species are lacking (more detailed morphological data and our results on variation in P. iwamae will be presented elsewhere). Dorsal color patterns, for example, vary even in a single locality, as demonstrated in

Two specimens of Plesiotrygon recently collected in November 2010 ( MUSM 39977) from the main channel of the Río Amazonas near the town of Tamshiyacu ( Peru), about 45 km upriver from Iquitos, are intriguing as they clearly cannot be identified with Plesiotrygon nana , but also differ slightly in coloration from “typical” specimens of P. iwamae (see Figures 23 , 25-27 ). Both specimens are comparable to P. nana in size (221 mm DL and 211 mm DW, 206 mm DL and 195 mm DW; Table 5), but are juvenile males, with claspers that are just beginning to protrude beyond pelvic fin posterior web ( Figure 26E ). They also differ significantly in having almost 10 more tooth rows, more caudal vertebrae, much fewer total pectoral radials (see Tables 2, 6), and many proportions of disc, snout, spiracles and eyes. In contrast, these specimens share with P. iwamae similar snout and disc proportions, disc shape, nasal curtain and spiracular proportions ( Table 5), tooth row counts, similar relatively low counts of pectoral radials, similar elevated counts of caudal vertebrae, creamy white color of filiform whip, conspicuous ventral lateral-line canal patterns (e.g. greatly inflected external hyomandibular canal), and a relatively stout hyomandibula (see Figures 23 , 24 ), but differ in dorsal coloration from smaller specimens of P. iwamae (such as MZUSP 14789). However, little is known concerning the dorsal color pattern of small specimens of P. iwamae . The dorsal color pattern of the Tamshiyacu material is somewhat similar to the paratypes of P. nana , and they were collected together with the preadult male paratype of this species. Given these uncertainties, we refer to these specimens as Plesiotrygon cf. iwamae until further material from the upper Amazon can be examined; we can ascertain, though, that they are much closer morphologically to P. iwamae than to the highly distinctive P. nana . These specimens from near Tamshiyacu are illustrated in detail here to serve as a basis for future comparison because small specimens of P. iwamae are lacking in collections. The smallest captured specimen of P. iwamae we have examined is the smaller male paratype from the Rio Solimões (230 mm DL, 215 mm DW). This lack of smaller material (not counting late-term embryos aborted by captured gravid females) may be an indication that their early life-cycle after birth takes place in deeper channels.

Figures

FIGURE 17: Paratype of Plesiotrygon iwamae in dorsal (A) and ventral (B) views (FMNH 94500, adult female, 565 mm DL, Río Napo, Ecuador).

FIGURE 18: Specimen of Plesiotrygon iwamae (MZUSP 59898, 432 mm DL, 425 mm DW) from the Rio Jutaí (Amazonas state, Brazil), in dorsal (A) and ventral (B) views.

FIGURE 19: Morphological details of Plesiotrygon iwamae. A) Dorsal view of anterior disc and head region (MZUSP 59896). B) Nasoral region (MZUSP 59898). C) Dorsal view of base of tail and pelvic fins (MZUSP 108773). D) Ventral view of pelvic fins (MZUSP 59897). E) Dorsal view of base of tail and tail region at caudal stings (MZUSP 59898). F) Lateral view of tail at caudal sting region, showing ventral tail-fold (MZUSP 59898). Scale bar = 5 cm.

FIGURE 20: Left posterolateral disc region in Plesiotrygon iwamae, showing some of the variation in dorsal disc color present in specimens examined. A) MZUSP 59896 (Rio Solimões, 470 mm DL, 460 mm DW). B) MZUSP 108706 (Rio Pará, 350 mm DL, 355 mm DW). C) MZUSP 108771 (Rio Pará, 292 mm DL, 294 mm DW).D) MZUSP 108772 (Rio Pará, 298 mm DL, 300 mm DW).E) 108776 (Rio Pará, 396 mm DL, 398 mm DW). F) MZUSP 108775 (Rio Pará, 452 mm DL, 442 mm DW).

FIGURE 23: Skeleton of Plesiotrygon cf. iwamae from radiograph (MUSM 39977, juvenile male, 1096 mm TL, 221 mm DL, 211 mm DW). Tail posterior to caudal stings not depicted in radiograph.

FIGURE 24: Skeleton and dermal covering in paratype of Plesiotrygon iwamae (FMNH 94500, adult female, 565 mm DL). A) Splanchnocranium and scapular region. B) Close-up of angular cartilage. C) Base of tail region showing arrangement of dorsal spines and denticles. Abbreviations: AC, angular cartilage; AOC, antorbital cartilage; HYO, hyomandibula; MC, Meckel’s cartilage; MES, mesopterygium; NA, nasal aperture; POP, postorbital process; PQ, palatoquadrate; PRO, propterygium; SC, spiraclular cartilage (anterior); SCP, scapulocoracoid.

FIGURE 25: Dorsal (A, C) and ventral (B, D) views of Plesiotrygon cf. iwamae (Río Amazonas, near Tamshiyacu, Loreto Department, Peru). A, B) MUSM 39977 (juvenile male, 221 mm DL, 211 mm DW). C, D) MUSM 39977 (juvenile male, 206 mm DL, 195 mm DW).

FIGURE 26: Morphological details of Plesiotrygon cf. iwamae. A, B) Dorsal view of anterior disc and head region. C, D) Nasoral region. E) Ventral view of pelvic fins and claspers. A, C and E based on MUSM 39977 (juvenile male, 206 mm DL, 195 mm DW); B and D from MUSM 39977 (juvenile male, 221 mm DL, 211 mm DW). Scale bar = 2 cm.

FIGURE 27: Anterior disc and head region depicting relative proportions of eyes and spiracles in (A) subadult male paratype of Plesiotrygon nana sp. nov. (MUSM 40243, 174 mm DL, 170 mm DW), and (B) juvenile male Plesiotrygon cf. iwamae (MUSM 39977, 221 mm DL, 211 mm DW). Scale bar in A = 1 cm; B = 2 cm.