Urogymnus acanthobothrium, Last, Peter R., White, William T. & Kyne, Peter M., 2016

Last, Peter R., White, William T. & Kyne, Peter M., 2016, Urogymnus acanthobothrium sp. nov., a new euryhaline whipray (Myliobatiformes: Dasyatidae) from Australia and Papua New Guinea, Zootaxa 4147 (2), pp. 162-176 : 163-173

publication ID	https://doi.org/ 10.11646/zootaxa.4147.2.4
publication LSID	lsid:zoobank.org:pub:B4F33480-68C2-4703-AE82-AA184F0FB2CD
persistent identifier	https://treatment.plazi.org/id/03BBC82E-9E27-8711-43A0-0557FAEBFC30
treatment provided by	Plazi
scientific name	Urogymnus acanthobothrium
status	sp. nov.

Treatment

Urogymnus acanthobothrium View in CoL sp. nov.

Mumburarr Whipray

( Figs 1–7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 Table 1)

Himantura View in CoL sp.: Fyler et al., 2009: 107, figs. 58 and 59

Himantura sp. 1: Naylor et al., 2012, tissue GN 2103 (specimen NT-96, not retained).

Himantura sp. 5: Last et al., 2016, tissues GN 2103, GN 13667, GN 16659, GN 16661, GN 16993, GN 17253, GN 17254 ( Fig. 3 View FIGURE 3 ).

Urogymnus sp. 5: Last et al., 2016, tissues GN 13667, GN 17253 ( Fig. 5 View FIGURE 5 ).

Holotype. WAM P. 34488-001, juvenile male 672 mm DW, West Arm of Cambridge Gulf, Western Australia, Australia, 15°33′ S, 127°59′ E, depth 2.2 m, collected by P. Kyne & G. Johnson, 11 Nov 2015. GoogleMaps

Other Material. 9 specimens (none retained). Global Cestode Database NT-96 (photographs; tissue accession GN 2103), adult female 1610 mm DW with embryo ~ 265 mm DW (size estimated from image), east of Wessel Islands, Northern Territory, Australia, 11°18′ S, 137° 0 0′ E, ~ 60 m depth, collected by J. Caira & K. Jensen, 17 Nov 1999 GoogleMaps ; PNG field accession 130034 (photograph; tissue accession GN 16659), female 1140 mm DW, east of Aibinio Island , Gulf of Papua, Papua New Guinea, 8°42′ S, 144° 0 7′ E, 18–20 m depth, 2 Dec 2014, collected by S. Tova GoogleMaps ; PNG field accession 230260 (tissue accession GN 16661), male 1000 mm DW, east of Aibinio Island , Gulf of Papua, Papua New Guinea, 8°36′ S, 144° 0 1′ E, 11–15 m depth, 11 Dec 2014, collected by S. Tova GoogleMaps ; PNG field accession 180028 (photograph; tissue accession GN 16993), late adolescent male 1030 mm DW, south of Deception Bay , Gulf of Papua, Papua New Guinea, 7°58′10′′ S, 144°38′50′′ E, 10–14 m depth, 6 Apr 2015, collected by S. Ohuesaho GoogleMaps ; PNG (no field accession number), photograph, adult male 1100 mm DW, Gulf of Papua, Papua New Guinea, 8°0 1′4′′ S, 144°40′2′′ E, 17–23 m depth, 2 Nov 2015, collected by National Fisheries Authority ; photograph, female 520 mm DW and juvenile male 580 mm DW (released alive), Wildman River , Northern Territory, Australia, 12°21′30′′ S, 132°0 8′30′′ E, depth 7.8 m, collected by P. Kyne & P. Feutry, 29 Aug 2013 ; photograph, juvenile male 390 mm DW (released alive; tissue accession GN 13667), West Alligator River , Northern Territory, Australia, 12°22′48′′ S, 132°15′33′′ E, depth 4.2 m, collected by P. Kyne & M. Grubert, 22 Oct 2013 GoogleMaps ; photograph, juvenile male 600 mm DW (released alive), Ord River , Western Australia, Australia, 15°16′42′′ S, 128°16′41′′ E, depth 8.7 m, collected by P. Kyne & G. Johnson, 7 Nov 2015 GoogleMaps .

Diagnosis. A species of Urogymnus distinguished by a combination of the following characters: disc elongate suboval, snout tip to axis of maximum width 53% DW; anterior disc margin not truncated, almost straight, lateral apices broadly rounded; preorbital snout broadly angular, angle 114°, with a very small apical lobe; preorbit long, length 26% TL, 2.1 times interorbital length; orbits small, protruded slightly; spiracle very large, 8.6% DW, 1.9 in orbit diameter; internasal distance 2.0 in prenasal length, 2.8 times nostril length; preoral snout length 2.6 times mouth width, 2.5 times internarial distance; caudal sting very large, length more than a 30% DW; mid-scapular denticles very small and inconspicuous; secondary denticles very small, rather widely spaced, band delimited but margin not sharply defined, band truncate forward of eye; minute upright tertiary denticles present, barely visible; low and short-based ventral tail fold present; dorsal disc colour variable, plain dark greyish brown to yellowish brown in juveniles, very finely and faintly mottled greyish white to yellowish brown in adults; ventral surface largely white, posterior disc without regular dark margins; tail beyond sting white in young, unknown but possibly paler than anterior tail in adults; propterygial radials 66, 3 times the number of mesopterygial radials; total vertebral segments (excluding synarcual) 151.

Description. Disc elongate suboval, width 94% of its length in holotype; robust, distinctly raised above midscapulocoracoid, maximum thickness 0.12 in disc width (DW); snout broadly angular, with a small but pronounced apical lobe, angle 114°; anterior margins almost straight, oblique to longitudinal axis of disc; lateral apices broadly rounded; posterior margin weakly convex, free rear tip narrowly rounded. Pelvic fins rather short, 21.2% DW; width across base 13.0% DW. Mature male unavailable for examination of adult clasper. Tail rather slender, whiplike, tapering evenly toward sting then becoming subcircular, length 2.18 times DW; base rather narrow, moderately depressed in cross-section, width 1.26 times height; caudal sting greatly enlarged, 30.3% DW, broad and strongly depressed. Ventral tail fold short (see Fig. 6 View FIGURE 6 ), base length 7.8% DW, 0.14 in length from cloaca to sting, 23.7 times maximum height, preceded and followed by short, low fleshy ridge; maximum fold height 21% tail height at same point.

Snout relatively long, strongly depressed; preoral snout length 2.61 times mouth width, 2.46 times internarial distance, 25.3% DW; direct preorbital snout length 2.06 times interorbital length; snout to maximum disc width 53.0% DW; interorbital space almost flat with slight medial depression; orbits small, slightly protruded, diameter 1.89 in spiracle length; eye length 4.06 in spiracle length, intereye distance 7.68 times eye length. Spiracles very large, subrectangular to suboval; situated dorsolaterally; anterior margin oblique and almost straight, its origin beneath mid-orbit; posterior margin straight and strongly curved. Nostrils rather small, laterally expanded slightly, outer margin almost straight, internasal distance 1.97 in prenasal length, 2.83 times nostril length. Nasal curtain skirt shaped, broad and rather short, width 2.07 times length; lateral margin weakly concave, smooth edged; posterolateral apex nested within broad groove; posterior margin very weakly fringed (fringes indistinct and margin forming an angular ridge), weakly double concave; fully overlapping upper jaw and almost touching lower jaw. Mouth arched slightly ( Fig. 3 View FIGURE 3 ); oronasal groove shallow, extending posteriorly from posterolateral edge of mouth to chin, posterior extremities slightly exceeding mouth width apart; skin on ventral surface of lower jaw strongly papillate, in a broad strip around lips. Mouth floor with 2 large, fleshy medial papillae, their height ~ 4 mm, separated by about ~ 6 mm; a much smaller ridge-like lateral papilla near each corner of mouth, widely separated from inner pair, height ~ 2.5 mm; medial papilla simple, subtriangular, rounded distally with irregular margin, longitudinally flattened, subequal in size; largest known individual (Global Cestode Database NT-96, 1610 mm DW) reported to have 5 central and 2 lateral oral papillae. Upper jaw mildly double concave with a bulbous synthesis, lower jaw triple concave; lower jaw interlocking with upper jaw internally (upper jaw deeply recessed in head). Teeth small, broadly subtriangular to rhomboidal, in quincunx; similar in size in upper and lower jaws; surfaces of crowns strongly crenulate. Tooth rows in upper jaw ~40, in lower jaw>40, difficult to count without further dissection.

Gill opening margins narrowly S-shaped, smooth edged; length of first gill slit 1.40 times length of fifth, 2.41 in mouth width; distance between first gill slits 2.33 times internasal distance, 0.44 of ventral head length; distance between fifth gill slits 1.71 times internasal distance, 0.32 in ventral head length.

Squamation. In holotype: Denticle band prominent, lateral disc appearing smooth but densely and evenly covered with minute upright subconical denticles (barely visible with naked eye or detectable by touch except margin of secondary band). Suprascapular denticles 3, very small (length of largest 2.6 mm), similar in size, barely larger than adjacent denticles of secondary band; surfaces irregular; upper surface of crown not obviously flattened. Secondary and tertiary denticles easily distinguishable from each other. Secondary denticles very small, rather widely spaced (interspaces almost half denticle width), heart-shaped, similar in size, usually directed posteriorly, not larger across scapular region than elsewhere in band. Secondary denticle band well developed on disc, extending from just forward of orbit across mid disc then tapering gradually and extending onto tail; margin of band somewhat irregular (not sharply demarcated as an edge); truncate forward of eye, continuous over entire interorbital space, narrowest on mid disc beside spiracles, broadest over scapular region; similar band of denticles extending onto entire dorsal and upper lateral surfaces of tail before caudal sting; similar denticles on lateral edge of tail beneath caudal sting; small prickly upright and rather widely spaced denticles present on tail posterior to sting (some similar denticles near sting base on dorsal base). Tertiary denticles minute, barely detectable, partially embedded, possibly increasing in size with ontogeny (needing confirmation). Ventral surface of disc naked.

Meristics. Total pectoral-fin radials 150; propterygium 66, mesopterygium 22, metapterygium 62. Pelvic-fin radials 1 (includes 3–4 distal elements fused at base) + 22. Vertebral centra (excluding synarcual) 151; monospondylous 57; pre-sting diplospondylous 94; post-sting diplospondylous 0.

Colour. Holotype (when fresh): Disc uniformly yellowish brown dorsally (denticle band similar to rest of disc but denticle crowns slightly paler than adjacent skin); skin also with a few small, irregularly spaced, darker speckles; disc margin with narrow white strip around pectoral fin anteriorly, becoming dusky posteriorly; pupil of eye black, spiracle whitish; anterior tail paler yellow, gradually becoming whitish forward of caudal sting base; sting and tail beyond sting uniformly white (strongly contrasted with yellowish disc); no information available for ventral surface.

Holotype (in preservative): Upper surface uniformly pale brownish with denticle band distinct and paler than surrounding disc; denticle crowns appearing as white specks; spiracle dark greyish interiorly, posterior margin white. Ventral surface of disc largely white, irregular light and dark grey patches centrally and on posterior parts of pelvic fins. Tail largely white above, more yellowish and typically darker ventrally; ventral base greyish with some greyish-brown patches before caudal sting; posterior quarter of ventral tail with a dark brown medial stripe; ventral fold pale brownish and white.

Non types (not retained and descriptions based on images): Late embryo (Global Cestode Database NT-96, Fig. 2 View FIGURE 2 A) similar to juvenile above, uniformly dark greyish brown dorsally, tail similarly greyish brown to caudal sting base; sting and tail beyond sting pale greyish. Juvenile male (tissue accession GN 13667, Fig. 2 View FIGURE 2 B) darker than adults, uniformly dark greyish brown dorsally, eye and spiracle darker; tail similarly greyish brown to caudal sting base; sting and tail beyond sting white. Female ( PNG field accession 130034, Fig. 2 View FIGURE 2 C mottled greyish yellow on outer dorsal disc with denticle band paler yellowish and distinct from rest of disc; spiracles bluish white and prominent; tail white near and beyond caudal sting; ventral surface uniformly white (outer pectoral fins pinkish due to skin damage). Adult male ( PNG, no field accession number, Fig. 2 View FIGURE 2 D) medium brown on dorsal surface and very finely mottled; clasper pinkish white. Adult female (NT-96, Fig. 2 View FIGURE 2 E) very finely and very faintly mottled greyish white on outer dorsal disc with denticle band paler yellowish and distinguishable from rest of disc; spiracles bluish grey and prominent; tail base similar to disc before caudal sting; tail missing beyond sting but possibly paler than anterior tail.

Size. Among the largest of all stingrays; adult female (1610 mm DW, 1740 mm disc length) aborted a late embryo (estimated to be ~ 265 mm DW) on capture. Juveniles (n=5) measured 390–672 mm DW, 430–720 mm DL. A late adolescent male (1030 mm DW) was captured off Papua New Guinea but not retained.

Distribution. Gulf of Papua, Papua New Guinea, and northern Australia ( Fig. 8), in brackish reaches of tidal rivers and estuaries, and marine waters. Juveniles have been recorded from lower reaches of the Wildman and West Alligator Rivers, Northern Territory (NT), and the lower Ord River and West Arm of Cambridge Gulf, Western Australia. Juvenile capture depths were 2.2–8.7 m; salinity 14.6–33.1; turbidity 367–>1000 NTU. An adult female was recorded in marine waters at a depth of 60 m east of the Wessel Islands, NT. Subadult specimens caught in the Gulf of Papua were from depths of 10– 20 m. Probably more widespread in remote and under-surveyed areas of northern Australia and Papua New Guinea, particularly within the complex river systems and associated coastal zones.

Etymology. A large female collected during a survey of cestode parasites of northern Australian chondrichthyan fishes yielded 4 species of cestodes of the genus Acanthobothrium (A. oceanharvestae, A. popi, A. rodmani and A. zimmeri) that are found only in this species ( Fyler et al., 2009). Hence, the epithet ‘ acanthobothrium’ is used as a noun in apposition to recognise the historical significance of the parasite project in the discovery of this whipray. The vernacular name ‘Mumburarr Whipray’ is used to acknowledge the assistance of Traditional Owners in locating this species, in particular the people of the Alligator Rivers region in the Northern Territory. Mumburarr is a local Limilngan language name used by the Minitja people of the West Alligator River region meaning stingray. Coastal, estuarine and riverine stingrays were traditionally hunted for food and the caudal sting was used as a traditional knife.

mm %

Disc width 672.0

Total length 2077.0 309.1 Disc length 718.0 106.8 Snout to pectoral-fin insertion 635.0 94.5 Orbit to pectoral-fin insertion 441.0 65.6 Snout to maximum disc width 356.0 53.0 Snout to origin of cloaca 611.0 90.9 Cloaca origin to tail tip 1466.0 218.2 Cloaca origin to caudal sting 386.0 57.4 Pectoral-fin insertion to caudal sting (horiz) 363.0 54.0 Disc thickness 82.0 12.2 Snout (preorbital) length 178.7 26.6 Snout (preorbital horiz.) length 166.6 24.8 Orbit diameter 30.3 4.5 Eye diameter 14.2 2.1 Spiracle length 57.5 8.6 Orbit and spiracle length 72.1 10.7 Interorbital width 86.6 12.9 Inter-eye width 108.7 16.2 Distance between spiracles 111.2 16.6 Head length 366.0 54.5 Preoral length (to lower jaw) 170.3 25.3 Prenasal length 136.1 20.2 Nostril length 24.5 3.6 Nasal curtain length 42.6 6.3 Nasal curtain width 88.1 13.1 Distance between nostrils 69.2 10.3 Mouth width 65.1 9.7 Distance between 1st gill slits 161.0 24.0 Distance between 5th gill slits 118.4 17.6 Width 1st gill slit 27.0 4.0 Width 3rd gill slit 29.0 4.3 Width 5th gill slit 19.3 2.9 Tail width, base of caudal sting 16.5 2.5 Tail width, axil of pelvic fins 53.7 8.0

......continued on the next page Conservation considerations. While at present there is insufficient data available to assess the extinction risk status of Urogymnus acanthobothrium sp. nov., it should be noted that euryhaline elasmobranchs are generally of conservation concern ( Lucifora et al., 2015). The limited number of existing records suggests that the new species may be naturally rare, and it is likely to possess life history characteristics of large elasmobranchs (i.e. late age at maturity, low fecundity, long lifespan, and low natural mortality) which result in low productivity and a limited ability to recover from population depletion ( Musick, 1999).

Juvenile U. acanthobothrium in northern Australia receive some refuge in Kakadu National Park where there is no commercial fishing. Juveniles have been recorded in the Wildman and West Alligator Rivers within the Park; access to the latter is completely closed (i.e. no boat access is permitted) providing a unique conservation zone. In the Kimberley region of Western Australia, commercial fishing activities are limited where juveniles have been recorded. The deployment of turtle exclusion devices (TEDs) most likely minimizes their capture in the Australian Northern Prawn Fishery as large rays can be effectively excluded from trawl nets ( Brewer et al., 2006). This fishery operates across northern Australia, including in the area where the first (adult) specimen was caught. Nevertheless, this species is caught as bycatch of trawling in the Gulf of Papua; that fishery is currently investigating the use of TEDs which would limit future catches of at least the largest specimens.

The sporadic records of U. acanthobothrium across northern Australia and the Gulf of Papua suggest a wider distribution than presently known, and an effort should be made to collect more comprehensive data on this species, particularly on its distribution, ecology and interactions with fisheries, to accurately assess its extinction risk status.

Comparisons. Urogymnus acanthobothrium sp. nov., which attains at least 161 cm DW, is amongst the largest whiprays. No other himanturin ray in the Indo-West Pacific has a ventral tail fold (present but very narrow in U. acanthobothrium ); a well-developed fold is present in the Atlantic whipray genus, Fontitrygon . Of species of Urogymnus , U. granulatus is also unusual in that it has a uniformly white tail, and appears to be closest to this species based on NADH2 data (see Figs 3 View FIGURE 3 & 5 View FIGURE 5 ; Last et al., 2016). Based on the holotype and data provided by Manjaji (2004) for U. granulatus , U. acanthobothrium has a longer (length ~2.5 vs 1.5–2.1 times combined orbit and spiracle length) and more angular snout (angle 114° vs 122–123°), longer tail (length 2.3–2.4 vs 1.3–2.1 times DW), more posteriorly positioned caudal sting (horizontal length from disc insertion to sting origin ~3.3 vs ~2 times interspiraclar width), more oval tail base (otherwise subcircular), lacks white flecks on the dorsal surface, and the ventral disc is uniformly white (rather than white with a broad black margin). Other members of the genus have a much more angular snout ( U. lobistomus ) or the snout is much more obtuse (almost truncate) anteriorly ( U. dalyensis and U. polylepis ). The type of the genus, U. asperrimus , also known as the Porcupine Ray, which has an extremely thorny dorsal surface unique within whiprays and lacks a caudal sting, is probably highly derived.

Initially, an enormous ray photographed by Mark Erdmann while diving near Raja Ampat (Papua) was thought to be conspecific with this species, but after subsequent examination of his photographs, it is more likely a very large Urogymnus polylepis ( Bleeker, 1852) . Urogymnus polylepis also reaches a huge size and specimens from the Chao Phraya River ( Thailand) measured 192 cm DW and at least 242 kg. A close relative from tropical Australia and probably New Guinea, Urogymnus dalyensis , is a much smaller ray (reported at 124 cm DW) that co-occurs with U. acanthobothrium in parts of this region. It remains a mystery how such a large coastal animal can escape detection for so long. However, the superficial similarity of these Urogymnus species in the region, and the paucity of comparative specimens in ichthyological collections because of their large size, are likely reasons.