Styracura, De Carvalho, Marcelo R., Loboda, Thiago S. & Da Silva, João Paulo C. B., 2016

De Carvalho, Marcelo R., Loboda, Thiago S. & Da Silva, João Paulo C. B., 2016, A new subfamily, Styracurinae, and new genus, Styracura, for Himantura schmardae (Werner, 1904) and Himantura pacifica (Beebe & Tee-Van, 1941) (Chondrichthyes: Myliobatiformes), Zootaxa 4175 (3), pp. 201-221 : 203-205

Styracura , gen. nov.

amphi-American Himantura .— Lovejoy, 1996: 215, 219, 221, 222, 228, 229, 233, 236–239, 241, 244–251 (morphology, relationships); Lovejoy et al., 1998: 421 (molecular phylogeny); McEachran & Aschliman, 2004: 80, 86, 88–92, 96, 98, 99, 101 (morphology, phylogeny); Carvalho et al., 2004: 76, 81, 84, 85, 90, 93, 98, 101, 103, 105–108, 112–115, 117–119 (morphology, relationships); Aschliman et al., 2012a: 64, 66, 68, 70–72, 75, 77, 79, 86–88, 90, 92–94 (morphology, phylogeny); Aschliman et al., 2012b: 30, 34–36, 38, 39 (molecular phylogeny); Last et al., 2016: 353, 356 (molecular phylogeny).

Type-species. Trygon schmardae Werner, 1904 .

Included species. Styracura schmardae ( Werner, 1904) ( Fig. 1 ), S. pacifica ( Beebe & Tee-Van, 1941) ( Fig. 2 ).

Definition. New world whiptailed stingrays distinct from dasyatid (including the Indo-Pacific urogymnin genus Himantura ), urotrygonid, and potamotrygonin genera by the combination of the following characters: disc rounded to weakly rhomboidal, about as wide as long or just slightly wider than long, with either relatively straight or slightly oblique anterior disc margins, and broadly rounded lateral pectoral apices; very small rostral protuberance present on anterior disc margin; disc posterior apices somewhat distant from tail base; head relatively broad and anteriorly positioned; eyes small, about one-third to one-half of spiracle length, and not significantly protruding above head; pelvic fins barely protruding beyond level of posterior disc; tail very elongate, its length measured from cloaca about twice snout to cloaca distance, and tail relatively slender, its posterior one-half whiplike; tail with low lateral ridges from level of pelvic fins to mid-distance to caudal stings; dorsal tail fold (or keel) lacking, low ventral tail fold (keel) present from level of caudal stings to short distance posterior to stings; tail width at base just smaller than interorbital distance; tail posterior to caudal stings at least two times caudal sting length; dermal denticles relatively large and blunt with a stellate pattern (with radiating and distally subdivided ridges), usually quadriradiate, closely packed (their very broad, circular to quadrangular basal plates frequently overlapping) and evenly distributed over almost all of dorsal disc and tail; slightly smaller asterisk-shaped denticles, with a single, pointed, more vertical crown and stellate basal plate and coronal ridges, present on disc margins and anterior to caudal stings on tail; two enlarged scapular denticles on shoulder region, these also with a stellate pattern but with numerous and more developed longitudinal crown ridges (slightly greater in S. schmardae than in S. pacifica ); pelvic fins and ventral surface devoid of denticles, but small, sharp denticles present posterior to caudal stings on ventral tail; caudal sting very developed, elongated (its length almost two times interorbital distance) and slender (only about as wide as whip-like tail at level of stings), and set far distally on tail, its distance from cloaca nearly equal to snout to cloaca distance; uniform grayish, grayish-brown, olivaceous-brown to purplish-brown disc, pelvic fins and tail base; tail darker except at base.

Internal morphological characters that further define Styracura include: antimeres of mandibular lateral-line canal meet posterior to mouth forming an inverted V-shape (not shown in Fig. 4 ); two short posterior subpleural tubules branch off from the subpleural component of the hyomandibular lateral-line canal; hyomandibular lateralline canal without median indentation on anterolateral disc; infraorbital canal sinuous but without reticulations and not forming suborbital loop; supraorbital canal relatively straight, forming a small posterior loop just anterior to nasal curtain; hyomandibulae with well-developed anterior segment; hyomandibular-Meckelian ligament well developed, posteriorly oriented toward midline, and with small calcified elements within; antimeres of m. spiracularis project posteroventrally to meet dorsal to the m. depressor hyomandibulae and ventral to m. coracomandibularis; scapular process fenestra present on scapulae; broadly triangular but short prepelvic process present; and anterolateral pelvic girdle margins relatively straight, not concave or convex.

Remarks. The classification of stingrays has recently undergone significant modifications to accommodate the latest developments in molecular phylogeny based on comprehensive species-level sampling and Maximum Likelihood analysis of the protein coding portion of the entire mitochondrial genome (Last et al., 2016; Yang et al., in prep). As a result, the Dasyatidae is now subdivided into four monophyletic subfamilies: Dasyatinae , Urogymninae, Hypolophinae, and Neotrygoninae (Last et al., 2016). The Urogymninae clade (whiprays) is composed of the genera Brevitrygon , Fluvitrygon , Fontitrygon , Maculabatis , Pateobatis , Himantura , and Urogymnus , the former five genera newly described in Last et al. (2016) and containing species previously placed in Himantura . Styracura is separated from all urogymnin species by readily observed external morphological characters such as its particular shagreen of denticles (quadriradiate morphology of larger denticles with broad basal plates and asterisk-shaped smaller denticles, and their intense distribution over disc and dorsal tail), its uniquely slender and very elongate caudal stings positioned far posteriorly on tail, and by presenting a low ventral caudal keel posterior to caudal stings. Styracura further differs from many urogymnin species by having a rounded to weakly rhomboidal disc (many urogymnin species have strongly rhomboidal discs; Manjaji, 2004; Last et al., 2016).

The posterior position and great development of the caudal stings also easily distinguish Styracura from potamotrygonin species. Furthermore, no potamotrygonin has enlarged scapular spines and dermal denticles as closely packed as in Styracura , nor its rounded to weakly rhomboidal disc shape ( Heliotrygon has an even more broadly rounded disc, Paratrygon usually has a concave anterior disc margin, and Potamotrygon and Plesiotrygon have more oval discs). Tail folds also distinguish Styracura from potamotrygonins: Potamotrygon usually has well developed dorsal and ventral tail folds posterior to caudal stings, Plesiotrygon has a well-developed ventral tail fold but a low dorsal ridge, and Paratrygon and Heliotrygon have very low, ridge-like ventral tail folds posterior to caudal stings (frequently lacking in adult specimens), while dorsal tail ridges are infrequently present in both genera. Moreover, the former three potamotrygonin genera have enlarged tail thorns, sometimes in multiple semiparallel rows, ahead of the caudal stings (tail thorns absent in Styracura ).

Etymology. From the Greek στυραξ (= styrax), meaning "spine at the butt end of a spear" ( Brown, 1954), and ουρα (= oura) meaning tail, a suffix commonly used since Müller & Henle (1837) for whiptailed stingrays—in reference to its greatly elongated caudal stings. Gender feminine.

Figures

FIGURE 1. Styracura schmardae (ROM 66845, juvenile female, 276 mm DW, Guyana) in dorsal (A) and ventral (B) views. Live color brown or grayish- to olivaceous-brown.

FIGURE 2. Styracura pacifica (ROM 66838, juvenile female, 287 mm DW, Pacific coast of Costa Rica) in dorsal (A) and ventral (B) views. Live color usually purplish-brown.

FIGURE 4. Ventral lateral-line canals of Styracura schmardae (MZUSP uncat. 508 mm DW). Abbreviations: HMD, hyomandibular canal (pink); IOC, infraorbital canal (blue); jug, jugular component of hyomandibular canal; NAS, nasal canal (including the prenasal canal anteriorly; yellow); pst, posterior subpleural tubules; spl, subpleural component of hyomandibular canal; SPO, supraorbital canal (green).