Strophurus horneri, Oliver & Parkin, 2014

Oliver, Paul M. & Parkin, Tom, 2014, A new phasmid gecko (Squamata: Diplodactylidae: Strophurus) from the Arnhem Plateau: more new diversity in rare vertebrates from northern Australia, Zootaxa 3878 (1), pp. 37-48 : 41-46

Strophurus horneri sp. nov.

Arnhem Phasmid Gecko

Figs. 2–4B

Holotype. NMV D72591, female, Yirrkakak , west Arnhem Land, Northern Territory, Australia (12°12'14"S, 133°48'03"E), collected by P. Horner, J. Melville & R. Glor, 9 November 2004.

Additional material. Tail tips in ethanol, all from Kakadu National Park, Northern Territory: MAGNT TS0053 , Namarragon Gorge, (12°54'39.42"S, 132°56'01.28"E) ; CCM2502 (13°38'20.67"S, 132°36'17.54"E) and CCM 2572 (12°51'41.40"S, 132°58'45.84"E), both held at the Australian National University, Canberra .

Diagnosis. A very small (SVL ~ 36 mm) and slender-bodied Strophurus with a narrow head (HW/SVL 0.15–0.16), no caudal spines or tubercles, rostral separated from the nostril by an internasal scale, a high number of relatively small supralabials (13–15), and body coloration in life consisting of four broad yellow longitudinal stripes on a greyish or brown background. As more specimens of this species are examined it may be confirmed that rostral not or only partially divided by a strongly defined medial groove is another useful diagnostic character. Males of all related taxa ( S. jeanae , S. robinsoni , S. taeniatus and Strophurus cf. horneri from elsewhere on the Arnhem Plateau) also lack post-cloacal or femoral pores, and it is presumed that this species also shares this character state.

Description of holotype. Female with following dimensions (mm): SVL 35.7; HW 5.6; HD 3.6; HL 8.8; EN 3.3; IN 1.5; EYE 2.1; Trk 17.5; Crus 5.3; Tibia 6.0; TL 24.2; TD 2.7; TW 5.6; 3FW 0.7; 3TW 0.8.

A very small (SVL <40 mm) and slender gecko ( Fig. 2 ). Head wide (HW/SVL 0.16) and flattened (HD/HW 0.64), much wider than body and distinct from neck; snout broadly rounded in dorsal profile, acute in lateral profile, longer than eye (EN/EYE 1.6), loreal region slightly concave, interorbital region and top of snout nearly flat, canthus rostralis indistinct. Eyes large, pupil vertical, fringe of projecting ciliaries extending from anteroventral to posterodorsal edge of eye, longest and distinctly acute at the anterodorsal corner, small slightly recurved postocular spines on right (5) and left (3) sides of the orbital. Ear opening on left near circular, slightly wider than high, opening on right obscured by folded skin. Rostral hexagonal, very flattened, approximately four times as wide as high, without a distinct medial groove, bordered dorsally by two semilunate nasals and two small granular internasals. Nares not in contact with rostral, bordered by semilunate nasal, first supralabial, and two enlarged postnasals; enlarged supralabials 13 on right and 15 left, 11 to midpoint of eye; first supralabial squarish, others tend to be rectangular or oval and somewhat wider than deep, generally no more than twice the height of dorsally adjacent scales. Head, temporal, and nuchal scales very small and granular, dorsal scales on snout noticeably larger. Infralabials 14 on right, 15 on left, all bordered ventrally by 3–4 rows of slightly enlarged scales grading into small granular gular scales, anterior infralabials rounded, as wide as deep, more than twice the depth of adjacent scales, medial and posterior infralabials somewhat rectangular, much wider than high and no deeper than adjacent scale series. Mental rounded, slightly deeper than wide, similar in shape and size to first infralabials, bordered posteriorly by two rounded postmentals.

Body slender and long (TrL/SVL 0.49), near circular in cross-section; ventrolateral folds clearly apparent behind forelimbs, present but less prominent along remainder of torso; body scalation small and granular, dorsum with larger rounded or triangular scales interspersed with much smaller intervening scales, ventral scales relatively homogenenous, grading larger medially, medial ventral scales up to twice width of lateral ventral scales.

Forelimbs moderately long and slender (Crus/SVL 0.15), hindlimbs slightly longer and also slender (Tibia/ SVL 0.17). Digits moderately long and well developed, some outer digits on hands and feet have preserved folded inwards making lamellae counts difficult; all digits with expanded subdigital lamellae, 4–5–5–6–5 on left hand, 4–4–4–5–5 on left foot, terminal lamellae paired and distinctly separated from penultimate lamellae, subsequent 2–3 subterminal lamellae much wider than deep, undivided although often with distinct posterior and anterior notches, proximal lamellae smaller and rounded; claws present on all digits, minute, not extending beyond terminal lamellae.

Tail original, broken along dorsal edge of autonomy plane, narrower and shorter than body (TL/SVL 0.68), distinctly inflated, widest around midpoint, slightly flattened (TW/TD 1.2). Caudal scales granular, heterogeneous, consisting of large round scales and much smaller intervening near triangular scales, arranged in relatively distinct segmented rows, much larger ventrally. Cloacal opening with no spurs or swellings.

Colouration in preservative. Base colouration medium to light brownish-grey ( Fig. 2 ); overlain by several darker stripes extending from the base of neck to tip of tail - a broad darker grey vertebral stripe, a pair of very thin brownish-grey paravertebral lines, a pair of broad light grey lateral stripes with distinctly darker edges, and a pair of indistinct thin lower lateral stripes. Head base colouration dark brownish-grey, slightly darker on crown than snout, with indistinct brown flecking and longitudinal lines on the snout, extensive light brown maculations around the supralabials, and a series of postorbital stripes that merge with lateral stripes on the torso.Venter greyish-cream with a few indistinct light brown longitudinal stripes on the anterior torso and numerous brownish spots or flecks on the throat. Limbs distinctly darker than torso on both dorsal and ventral surfaces, with scattered indistinct darker flecks, and faint broad striping on the ventral surface of the hindlimbs. Dorsal and lateral pattern of tail similar to torso with alternating wide vertebral, thin paravertebral and wide lateral stripes on a grey background; ventral surfaces light creamish-grey with three thin darker grey stripes.

Colouration in life. A photograph of the holotype in life ( Fig. 3 ) shows the areas of the dorsum and tail that are very light in preservative have a very clear yellowish wash and form four distinct longitudinal stripes that contrast strikingly against the bordering areas which are light to almost bluish grey with very fine light brown flecking. The iris is light grey with extensive very fine light brown vermiculations, while the pupil is elliptical with distinctly scalloped edges.

Variation. Photographs of additional specimens were kindly provided by Stuart Young and Brendan Schembri ( Figs. 4A–B ). Both have the same basic dorsal pattern of four yellow longitudinal stripes on a medium grey background. The yellow stripes on these specimens are slightly brighter and their edges are more strongly defined than on the holotype. The posterior dorsum of the head in one specimen also has distinct large yellow maculations ( Fig. 4A ). The tongue is pink ( Fig. 4B ).

Comparisons with other taxa. Strophurus horneri sp. nov. is distinguished from most Strophurus ( S. assimilis (Storr) , S. ciliaris (Boulenger) , S. intermedius (Ogilby) , S. krisalys Sadlier , S. rankini (Storr) , S. spinigerus (Gray) , S. strophurus (Duméril & Bibron) , S. taenicauda (De Vis) , S. wellingtonae (Storr) and S. williamsi (Kluge)) by its smaller size (SVL <50mm) and further differs from most of these species by lacking distinctive rows of tubercles or spines on the tail. It also presumably further differs in lacking post-cloacal or femoral pores, however this needs to be confirmed.

Of the six remaining species of Strophurus which lack caudal spines and are generally also found in association with spinifex or other grasses, Strophurus horneri sp. nov. can be distinguished from S. elderi , S. jeanae , and S. michaelseni (Werner 1910) by the presence of an internasal scale separating the rostral scale from the nostril (vs rostral in contact with the nostril); from S. mcmillani by its smaller size (adult SVL ~ 36.0 mm vs 40.3–49.1 mm) and less robust build (HW/SVL ~ 0.15 vs 0.17–0.19); and from S. robinsoni by its smaller adult size (SVL ~36.0 mm vs 53.0–56.0 mm), less robust build (HW/SVL ~ 0.15 vs 0.17–0.19), and dorsal pattern consisting of alternating yellow and grey stripes (vs very thin discontinuous dark grey longitudinal striations on a light grey background).

It differs from its geographically proximate sister species S. taeniatus in having smaller and more numerous supralabial scales (13–15 vs 10–12) and four wide yellow longitudinal stripes on a greyish or brown background (vs usually a more complicated pattern of three wide brown stripes and four much thinner yellow stripes). It also tends to have a relatively plain venter and throat pattern of small brown flecks or at most a single very thin continuous longitudinal stripe (vs usually three pairs of near continuous, thin greyish stripes). Some or all populations of S. horneri sp. nov. may also differ from S. taeniatus in having the rostral not or only partially divided by a clear crease, but more material is required to confirm this.

Distribution and habitat. Strophurus horneri sp. nov. is known only from the Arnhem Plateau region in the Top End of the Northern Territory. The holotype was collected on the northern edge of the Arnhem Plateau in the vicinity of Yirrkakak. Other specimens have been observed at other localities along the western edge of the Arnhem Plateau (Brendan Schembri, Mitchell Scott pers. comm.), and this species may occur throughout the western and northern Arnhem Plateau ( Fig. 1 ).

Where data is available, all specimens were found in well developed spinifex patches on or at the base of large sandstone escarpment or boulders ( Fig. 5 ). The longitudinal striped patterning evident in life provides excellent camouflage in this habitat. Brendan Schembri (pers. comm.) reports that this species was comparatively easy to find in long unburnt spinifex in a sheltered gully in southern Kakadu. The potential role of fire frequency in shaping the distribution and abundance of this taxon warrants further investigation.

Etymology. Named in honor of Dr. Paul Horner, Emeritus Curator of the Museum and Art Gallery of the Northern Territory, in recognition of his significant contributions to Australian reptile systematics.

Figures

FIGURE 1. Map of northern Australia showing position of the Arnhem Plateau (dark grey region at centre top of Australia), and localities for the single voucher of Strophurus horneri sp. nov. (dark grey circle), sites for additional material of Strophurus horneri sp. nov. (grey circles) and Strophurus cf. horneri (white circles with central dot), and museum records for Strophurus taeniatus (white squares) from across northern Australia.

FIGURE 2. Dorsal and ventral view of holotype of Strophurus horneri sp. nov. NMV D72591. Scale bar =1cm. Photograph courtesy Museum Victoria.

FIGURE 3. Strophurus horneri sp. nov. in life. Holotype NMVD72591 photographed at Yirrkakak. Photograph courtesy Rich Glor.

FIGURE 4. A) Strophurus horneri sp. nov. seen and photographed in southern Kakadu National Park. Note prehensile tail and pink tongue. Photograph courtesy Brendan Schembri. B) Strophurus horneri sp. nov. captured and released at Namarragon Gorge, Kakadu NP. Photograph courtesy Stuart Young. C) Strophurus taeniatus from Wongalara Sanctuary. Note thinner yellow lateral stripes. Photograph courtesy Stephen Zozaya.

FIGURE 5. Habitat of Strophurus horneri sp. nov. at Namarragon Gorge, Kakadu National Park. The specimen in Fig. 4B was captured at night in a spinifex clump at this locality. Photograph courtesy Stuart Young.