Himantura hortlei, Peter R. Last, Mabel Manjaji-Matsumoto & Patricia J. Kailola, 2006

Peter R. Last, Mabel Manjaji-Matsumoto & Patricia J. Kailola, 2006, Himantura hortlei n. sp., a new species of whipray (Myliobatiformes: Dasyatidae) from Irian Jaya, Indonesia., Zootaxa 1239, pp. 19-34 : 22-33

Himantura hortlei new species

(Figs. 1-7, Table 1)

Himantura sp. E (Manjaji, 2004)

Material

Holotype. CSIRO H 5155-01, 707 mm DW, mature male, Minajerwi River estuary, Irian Jaya, 4°56’S, 137°03’E, 7 m, 25 Aug. 1998.

Paratypes. 10 specimens: CSIRO H 5285-01, 268 mm DW, immature male, Ajkwa River estuary, Irian Jaya, 4°53’S, 136°55’E, 4 m, 14 Aug. 1999 ; CSIRO H 4915-01, 282 mm DW, immature male, Ajkwa River estuary, Irian Jaya, 4°53’S, 136°55’E, 4 m, 24 Aug. 1998 ; CSIRO H 4917-01, 246 mm DW, female, Poriri Island, Irian Jaya, 4°56’S, 136°52’E, 4 m, 1 Jun. 1998 ; CSIRO H 4916-01, 327 mm DW, female, Ajkwa River estuary, Irian Jaya, 4°52’S, 136°56’E, 2 to 5 m, 24 Aug. 1998 ; CSIRO H 4549-02, 426 mm DW, female, Ajkwa River estuary, Irian Jaya, 4°58’S, 136°50’E, 3 to 6 m, 7 Feb. 1997 ; CSIRO H 5977-01, 654 mm DW, female, Merauke, Irian Jaya, 8°31’S, 140°22’E, 8 Oct. 2002 ; CSIRO H 5977-02, 240 mm DW, female, same data as CSIRO H 5977-01 ; CSIRO H 5980-05, 233 mm DW, immature male, Merauke, Irian Jaya, 8°31’S, 140°22’E, 9 Oct. 2002 ; CSIRO H 5980-06, 202 mm DW, female, same data as CSIRO H 5980-05 ; CSIRO H 5981-04, 472 mm DW, female, Merauke, Irian Jaya, 8°31’S, 140°22’E, 10 Oct. 2002 .

Diagnosis. A Himantura with the following combination of characters: disc subcircular, very angular anteriorly, length 1.1 times DW; pectoral-fin apices broadly rounded; snout extremely elongate, 11-18 times orbit diameter, angle 96-99o; snout to maximum disc width 52-58% of DW; orbit very small, diameter 0.4-0.5 of spiracle length, 3.8-6.3 times in interorbital distance; mouth not greatly protrusible; prepelvic process not expanded; 1-3 enlarged, flattened, pearl-shaped mid-scapular denticles; denticles of main band in two main sizes in adults, crowns plate-like to heart-shaped; dorsal disc uniformly yellowish, brownish, or greyish; ventral surface of adults usually canary yellow in fresh material, often black around oronasal region and gill slits; pectoralfin radials 135-143; pelvic-fin radials 22-28; total vertebral centra 99-108.

Description. Disc anteriorly produced, subcircular, length slightly exceeding width (Figs 1-3); length 1.08 times width in holotype (1.09-1.12 in paratypes); greatest width 1.01 (1.00-1.02) times distance from tip of snout to pectoral-fin insertion; not raised greatly above cranium (slightly more so above nuchal region), relatively less elevated in smallest paratypes; thickness 11.3% (8.0-11.5%) of disc width (DW); snout extremely elongate, pointed, angle 97.5o (96-99o); snout apex acute, narrowly triangular; anterior margin of disc strongly concave; pectoral apex broadly rounded, posterior margin moderately convex, free rear tip narrowly rounded. Pelvic fins short, 19.4% (17.0-21.0%) DW; paddle-shaped, anterior margin almost straight, posterior margin broadly convex; width across base 11.5% (11.0-12.0%) DW. Tail very elongate, extremely slender, postcloacal tail 2.67 (3.26-3.42, in two paratypes, other three with tails damaged) times precloacal length; base moderately depressed, width 1.39 (1.22-1.56) times height, strongly convex above, less so below; tapering evenly to half pre-sting length, becoming subcylindrical in cross-section toward sting; weakly hexagonal to almost rounded in cross section at sting base, width 1.08 (0.85-1.09) in height; beyond sting becoming much more slender, whip-like, quadrangular in cross-section, dorsal surface strongly convex, variable laterally, ventral surface distinctly flatter; tapering very gradually distally to bluntly pointed tip (acute in some small paratypes); shallow groove on mid-ventral surface beneath stinging spine often with a low fleshy median ridge; no obvious skin folds on tail.

Snout extremely long, very depressed, preoral snout length 5.02 (4.69-5.09) times mouth width, 3.56 (3.33-3.77) times internarial distance, 38.7% (37.1-38.4%) of DW; direct preorbital snout length 2.84 (2.52-3.04) times interorbital length; horizontal preorbital snout length 2.75 (2.45-2.96) times interorbital length; snout to maximum disc width 51.7% (51.7-57.9%) of DW; interorbital space very broad, flat; eyes greatly reduced, not elevated or protruding, orbit diameter 0.40 (0.43-0.53) in spiracle length, eye diameter 0.22 (0.24-0.31) in spiracle length; interorbital distance 6.20 times orbit diameter in holotype, much less (3.81-4.68) in young paratypes (246-430 mm DW). Spiracles tearshaped, very large, situated dorso-laterally. Nostril almost oval; anterior margin fleshy, subsiding into internasal aperture, occupying more than half length of external opening of nostril; anterior nasal fold membranous, well-developed; posterior lobe broad, tall; internasal distance 0.34 (0.31-0.36) in prenasal length, 2.93 (1.70-3.11) times nostril length. Nasal curtain subrectangular (Fig. 4), relatively broad, flat, width 1.75 (1.72-1.87) times length; lacking a longitudinal medial groove; posterolateral apex lying within broad groove of posterior nasal flap; lateral margin almost straight (sometimes weakly double concave), smooth edged; posterior margin weakly fringed, slightly concave (sometimes weakly double concave), falling just short of mouth or reaching level of upper jaw symphysis.

Upper jaw strongly arched, double concave, bulging outward slightly at symphysis; lower jaw double convex, similar in large and small specimens, symphysis strongly indented, partly recessed in upper jaw; no prominent oronasal grooves, weak lateral grooves skirting corners of mouth. Mouth not greatly protrusible; no distinct circumoral or internasal papillae, skin on chin feebly corrugated, except around lips; floor lacking oral papillae; palate with median fleshy longitudinal ridge. Teeth small, blunt, well spaced (more closely-set in juveniles), arranged quincuncially (Fig. 5); rows in upper jaw 25 (21-22); rows in lower jaw 28 (24-27); shape variable, bases suboval to rhomboidal, similar in both jaws; crown surface irregular, crenulated with low transverse ridges; crown tilted lingually in holotype, appearing wedge-shaped; in small paratypes, crowns more flattened, not imbricate, varying slightly in size and form continuously across jaw, largest at or adjacent symphysis, smallest near mouth corners.

Gill openings distinctive, strongly s-shaped, anterior margin forming a prominent fringed lateral lobe; length of first gill slit 0.95 (1.32-1.84) times length of fifth gill slit, 0.43 (0.32-0.44) in mouth width; distance between first gill slits 1.77 (1.59-1.82) times internasal distance, 0.32 (0.29-0.33) in ventral head length; distance between fifth gill slits 1.30 (1.21-1.30) times internasal distance, 0.23 (0.22-0.24) in ventral head length.

Prominent reticulating network of paired, subcutaneous, sensory canals interspersed between denticles of main band; medial supraorbital patch extending from near anterior extremity of band, across interorbital region to about a spiracle length behind spiracle; smaller lateral patch adjacent nuchal region; larger submarginal patch covering more than half of postorbital disc; narrow longitudinal patch from mid-disc (just posterior to level of nuchal region) extending to posterior disc and along lateral and dorsolateral surfaces of tail anteriorly, more widespread over tail beyond sting. Ventral lateral line network very well developed, strongly reticulated; holotype damaged, viscera removed by collector.

Total pectoral radials 135-137 (136-143); propterygials 54-57 (54-58), mesopterygials 26-30 (26-33) and metapterygials 51-54 (52-57). Total pelvic radials 23+1 (22-24+1 in two male paratypes, 23-28 in three female paratypes). Total vertebral segments (centra) 99 (99-108); postcranial monospondylous centra 44 (41-46); diplospondylous centra 55 (53-65).

Squamation. The stages of development of the denticle band (Fig. 6) are described as follows. Only stages 0, 2 and 4 are applicable to this species:

Stage 0: birth size unknown (but probably ca. 200 mm DW, Fig. 6A) -- smallest specimens (CSIRO H 5980-06, 202 mm DW, female; CSIRO H 4917-01, 246 mm DW, female) with naked disc, except for 3 prominent, embryological suprascapular denticles; central denticle pearl-shaped, adjacent denticles more longitudinally constricted, weakly angular posteriorly; distal snout with a few minute, barely noticeable, denticles. Tail denticles minute, conical, somewhat granular; widely scattered over dorsal half of poststing tail.

Stage 2: (ca. 250 mm DW, Fig. 6B, C) -- Development of secondary median denticle patch around suprascapular denticles (CSIRO H 5977-02, 240 mm DW, female); patch then begins to extend along midline anteriorly towards head with isolated denticles on snout (CSIRO H 5980-05, 233 mm DW, immature male); patch then begins to expand laterally over scapular region (CSIRO H 5285-01, 268 mm DW, immature male) to eventually form a well-developed band extending over mid-disc from anteriormost edge of vertebral ridge (at junction of cranium and vertebral column) to hind disc and expanded laterally over scapulocoracoid; additional widely spaced denticles appear on head and become denser on snout (CSIRO H 4915-01, 282 mm DW, immature male). Secondary denticles similar in size and shape; low with flat, weakly heart-shaped crowns; smaller interstitial denticles not evident, well separated, not imbricated; emerging denticles present as scars around periphery of band.

Stage 4: (>300 mm DW, Fig. 6D) -- In early part of this stage (CSIRO H 4916-01, 327 mm DW, female), secondary denticle band extends anteriorly over cranium as a narrow band anteriorly; becoming markedly broader over gills (subequal in width to interspiracular distance) and gradually narrowing posteriorly to almost reach level of pectoral-fin insertion; single row extending along midline of tail. During mid-part of this stage (CSIRO H 4549-02, 426 mm DW, female), secondary denticles forming a continuous, broad, suboval band on disc with moderately well-defined margins; band width greatly exceeding interspiracular distance, broadly expanded beside eyes; extending well forward of orbits anteriorly, following anterior profile of disc, pointed apically; posteriorly narrowing gradually, evenly, weakly truncated near pectoral-fin insertion, before joining band on tail; small, erect denticles scattered on anterior snout margin. Denticles of main band flat, heart-shaped, closely set; small, decreasing appreciably in size towards disc margin; interspersed with smaller irregularly shaped interstitial denticles.

Late Stage 4: (>600 mm DW, Figs 6E, F) -- Holotype (CSIRO H 5155-01, 707 mm DW, mature male) with fully developed, secondary denticle band. Band regular, very broad, continuous, its lateral margins sharply defined (pectoral fins naked lateral to band); broadest beside spiracle, narrowing only slightly between orbit and scapular region; band sub-triangular forward of orbits, its anterolateral margin slightly convex, almost paralleling profile of disc. Snout mostly naked forward of main band, with scattered denticles, densest near snout tip, naked proportion of snout 35.1% (54.1%, in one paratype with an almost fully-developed denticle band); well-defined naked patch around orbit, broadest over interspiracular region and below eye; orbital membrane naked; band weakly truncate posteriorly, expanded slightly before junction with tail series. Denticles mainly irregular, small, low, broad-based, non-imbricated, with flat crowns; variable in size but represented by two main forms; larger denticles (ca. 1-2 mm diameter) mostly heartshaped, somewhat regularly spaced, these separated by smaller interstitial denticles (ca. 0.5 mm diameter); smaller denticles more variable in shape, usually weakly heart-shaped, oblong or oval; all denticles typically decreasing in size laterally, minute along lateral margin of band; denticles abruptly terminating at margin of band. Suprascapular denticles not pronounced; denticles slightly larger than those adjacent, well separated, not aligned in a linear row, their margins irregular in shape; largest in holotype (ca. 4 mm diameter), subcircular, crown apex flat; interorbital denticles similar in size to those adjacent suprascapular patch. Denticles on snout small, sharp and pointed, especially dense near apex; bases subcircular, with short, slender, upright, pungent spiny crowns; those merging with main denticle band broad based, with scalloped posterior margins, weakly heartshaped. Outer disc beyond denticle band largely naked; pelvic fins naked. Tail denticles in a band (Fig. 7), extending onto dorsal half of tail anteriorly, progressively covering more of ventral tail toward sting; pre-sting tail otherwise almost completely naked. Beyond sting, denticles uniformly covering entire tail surface, not uniform in shape, not denser or enlarged along dorsal surface; denticles either short, blunt and conical, or smaller with flattened heart-shaped or oblong crowns; below sting smaller types predominate; near tail tip denticles less dense, shorter, predominately conical in shape. One or two stings present; one sting in holotype (damaged) and two paratypes, second sting developing above first sting in another paratype (CSIRO H 4916-01); distance of sting base from pectoral fin insertion 33.0% (32.5-35.2%) in DW, and 30.5% (29.8-31.87 %) in disc length. Second sting likely to be similar in shape to first sting, may be smaller; appearing above first sting during squamation Stage 2. Ventral surface naked.

Coloration. In preservative, dorsal surface of holotype uniformly dark brown, paler brown in female paratypes; when fresh, adult female yellowish (Fig. 2); darker, greenish grey in small juveniles (Fig. 3). Denticles paler than skin, whitish to pale green. Ventral surface of disc and pelvic fins mostly whitish (vivid yellow in fresh material) with a narrow dark margin (broadest in holotype); some dark blotches and dark borders around nostrils, mouth and gill slits of holotype, these regions paler, dusky in paratypes and sometimes obscure; tooth bands dark brown or orange in adult holotype and one young paratype (CSIRO H 4916-01, 327 mm DW), otherwise white. Tail almost uniformly brownish; typically paler, sometimes almost white, before sting.

Size. The largest specimen, the holotype (707 mm DW and 2396 mm TL), is a sexually mature male. Birth size and lengths at first maturity of males and females are unknown. The smallest female (202 mm DW) is almost naked, except for embryonic suprascapular denticles and granular denticles on the tail.

Etymology. Named after Mr. Kent Hortle who initially supplied the first photographs of the new species. He later specially collected fresh specimens for the type series from southern Irian Jaya.

Common name. Hortle’s Whipray.

Distribution. Southern Irian Jaya and possibly adjacent Papua and New Guinea. Not known from the coasts of nearby northern Australia and other Indonesian islands west of the Wallace line despite recent market surveys of elasmobranchs of these regions by one of the authors (i.e. P. Last).

Comparisons. Himantura hortlei belongs to the ‘ uarnacoides ’ species complex and can be distinguished from its close congeners by proportional measurements, coloration, squamation, and skeletal morphology as discussed by Manjaji (2004). This species group provisionally includes H. uarnacoides (Bleeker, 1852) , H. pastinacoides (Bleeker, 1852) , H. chaophraya Monkolprasit and Roberts, 1990 , H. granulata (Macleay, 1883) , and another closely related, undescribed species from Borneo, Himantura sp. F (Manjaji and Last, in press).

Unlike other nominal members of this species group, H. hortlei has a much longer, more angular snout (length 37.6-39.4% vs 18.8-34.3% DW), smaller eyes (diameter 1.2-2% vs 1.8-6.1% DW), a strongly reticulate, ventral lateral-line canal system (less well developed in all but H. chaophraya ), no oral papillae (versus 2-7), and a vivid yellow ventral surface in adults. Himantura hortlei also has a thinner disc than H. uarnacoides and H. pastinacoides (about 8-11.8% DW versus 12.0-12.8% DW in the other species). The undescribed whipray, H. sp. F is most similar to Himantura hortlei . It also lacks oral papillae but instead has a thin skin fold. Both H. hortlei and H. sp. F are yellowish or brownish on the dorsal surface in adults, but H. hortlei has a distinct dark upper border around the eye and spiracular margins, and is dark along the ventral margin of the disc (rather than uniformly white). Morphologically, both species look very much alike externally, with several shared characteristics i.e. general disc shape, long-snout, small eyes, and uniform dorsal colouration. However, analyses of morphometric data and x-ray counts, and closer examination of the external and internal characters revealed significant differences between the two species. Distinguishing features of H. hortlei include a relatively larger snout lobe, slightly longer snout (length 37.6-39.4% versus 36.5-37.9% DW in H. sp. F ), fewer propterygial radials (54-58 vs 63-65), presence of denticles on the upper anterior snout margin (otherwise absent), darker spiracular margins, a broader nasal curtain (length 11.1-12.1% versus 10.4-10.7% DW), a more strongly arched lower jaw that is not greatly protrusible, a fringed gill-slit margin (rather than smooth), and no anterolateral process in the pelvic girdle (otherwise present). It also has a relatively narrower disc (length 108-112% compared to 112-114% DW).

Remarks. The invalid combination Himantura nasuta (unpublished manuscript by L. W. Filewood, p. 29) for a stingray collected in Pai’ia Inlet (Gulf of Papua) appears to be of a form conspecific with H. hortlei . The epithet nasuta has been used for a skate, Raja nasuta Mueller & Henle (family Rajidae), that occurs in the Indo-West Pacific (Eschmeyer, 2006), but no valid nominal taxon having this epithet exists in the Dasyatidae.

Last & Séret (1999), in an analysis of the biogeographic patterns of Indo-Pacific chondrichthyan faunas, found that the Myliobatiformes, which includes the eaglerays and stingrays, is the dominant ordinal-level ray group in the Australasian region. They identified a need for further exploration, especially along the continental slopes off New Guinea and eastern Indonesia, to obtain a better understanding of the regional biodiversity. The discovery of this large, shallow-water ray further highlights the inadequacy of current survey coverage of the region.