Litoria stellarum, Richards & Johnston & Oliver, 2025

Richards, Stephen J., Johnston, Gregory R. & Oliver, Paul M., 2025, A new montane species of stream-dwelling treefrog (Pelodryadidae) from the Star Mountains, Papua New Guinea, Zootaxa 5661 (2), pp. 221-236 : 223-230

Litoria stellarum sp. nov.

urn:lsid:zoobank.org:act:8D147850-24E3-490C-A591-584A855CE0E8

Star Mountains Torrent Treefrog

Figs 1–3

Holotype. SAMA R71763 (FN USNM [SJR]209377), adult male, Dokfuma Meadow , Star Mountains , West Sepik Province, Papua New Guinea (5.0220°S, 141.1171°E; 3,200 m a.s.l.) by S.J. Richards and G. Johnston on 17 November 1991.

Paratypes. SAMA R71762 (FN USNM [SJR]209375), PNGNM (FN USNM [SJR]209376) , both adult males, same collection details as holotype.

Diagnosis. Distinguished from all other Litoria by the following unique combination of characters: 1) size medium (SVL of three males 36.1–41.8 mm, female unknown); 2) snout rounded in dorsal profile, acuminate in lateral profile; 3) vomerine teeth present; 4) males with vocal slits; 5) finger webbing basal, thick, fleshy, not extending beyond proximal subarticular tubercle on finger 4; 6) toes no more than 3/4 webbed; 7) heels without prominent dermal spike or lappet; 7) supratympanic skinfold nearly straight; 8) ear less than ½ diameter of eye (EAR/EYE 0.33–0.43); and 9) dorsal colouration brown, sometimes overlain with large pale green lateral and anterior blotches.

Description of holotype. An adult male of medium size (SVL = 41.8 mm) with vocal slits and nuptial pads. Morphometric data are summarised in Table 1 . Body moderately robust for a Melanesian pelodryadid ( Fig. 1A ). Limbs short (TL/SVL 0.54). Head moderately broad (HW/SVL 0.32), slightly narrower than long (HL/SVL 0.33, HW/HL 0.97). Snout narrowly rounded in dorsal view ( Fig. 2A ), protruding distinctly beyond lower jaw and sloping sharply back to tip of lower jaw in lateral view, tip acuminate ( Fig. 2B ); canthus rostralis well defined, narrowly rounded, slightly curved; loreal region steeply sloping, slightly concave, lips flared; nostrils slightly closer to tip of snout than eyes, oriented laterally; internarial distance much greater than distance from external naris to eye (EN/IN 0.67, IN/SVL 0.11, EN/SVL 0.07); eyes moderately small (EYE/SVL 0.11) but prominent, protruding in dorsal and lateral views; pupil horizontal. Tympanum small (TYM/SVL 0.04), one third diameter of eye (TYM/ EYE = 0.33), annulus poorly defined, dorsal edge obscured by short, nearly straight supratympanic ridge ( Fig. 2B ). Vomeropalatines forming two narrow elevations between choanae, left elevation more prominently raised than right, each with six distinct teeth; an additional small, isolated vomeropalatine elevation present on each side, located anterolaterally of choanae; tongue large, covering most of mouth floor, broad with barely detectable shallow posterior notch; vocal slits lateral, short, extending approximately 3 mm anteriorly from near angle of jaws.

Skin on dorsum and dorsal surfaces of limbs smooth in preservative, with scattered small tubercles in life, skin on chest and throat very finely granular, on belly and ventral surfaces of thighs moderately granular. Heel with low, poorly defined tubercle; series of low, pale tubercles around vent. Limbs without dermal folds.

Fingers moderately long with expanded terminal discs (3FD/SVL 0.06, 3FD/3FP 1.64) with distinct marginal grooves. Subarticular tubercles prominent, rounded, except distal-most tubercle on Finger 3 compressed, possibly artifact of preservation ( Fig. 2C ); inner metacarpal tubercle elongate, outer metacarpal tubercle broad, flat. Nuptial pad large, pale brown, finely granular, extending 3.7 mm along outer edge of Finger 1. Relative lengths of fingers: 3>4>2>1. Fingers nearly free of webbing, web restricted to thick, fleshy fringe at base of fingers 3–4 and along outside of finger 2 ( Fig. 2C ).

Toes moderately long with expanded terminal discs (4TD/SVL 0.05, 4TD/4TP 1.4) with distinct marginal grooves; disc on Toe 4 smaller than disc on Finger 3 (3FD/4TD 1.10). Subarticular tubercles moderately prominent, rounded, except distalmost subarticular tubercle on Toe 4 compressed, possibly as artifact of preservation ( Fig. 2D ); inner metatarsal tubercle well developed, oval; no outer metatarsal tubercle. Relative lengths of toes 4>5>3>2>1. Toes about ¾ webbed, webbing thick and fleshy, on outside of Toe 1 reaching distal subarticular tubercle, on inside of Toe 5 and outside of Toes 2 and 3 extending to approximately midway between distal subarticular tubercle and base of disc, and on both sides of Toe 4 to slightly beyond distal edge of middle subarticular tubercle ( Fig. 2D ).

Colour in preservative. Dorsum with dark-brown base colouration, bordered on both sides by two large, relatively symmetrical paler brown dorsolateral blotches that extend from forelimbs to groin ( Fig. 3 ); posterior region of head including orbitals dark brown, snout overlain by large clearly margined greyish brown triangular patch. Side of head dark brown with pale brown blotch under eye, lower lateral regions of torso mid brown, overlain with scattered small dark-brown blotches. Exposed surfaces of arms and legs dark brown, dorsal surfaces of digits dark brown, with exception of Fingers 1 and 2 which are light brown. Ventral surfaces buff, heavily overlain with darker brown blotches and punctations, especially on throat, middle regions of torso, and lower forearms. Underside of fingers and toes mid-brown, becoming noticeably lighter towards, and especially on, underside of discs.

Colour in life. Base colouration on dorsum, upper torso and exposed surfaces of limbs dark brown with limbs slightly lighter than dorsum; large lateral blotches along sides of body and triangular patch on snout light green with sparse and very scattered light brown vermiculations (snout) or dark punctations (lateral regions of torso). An additional light green patch posterior to eye extends along edge of lower jaw. Iris silver, heavily flecked with brown, giving appearance of overall orange-brown hue.

Variation. Morphometric variation among the three types specimens is presented in Table 1 . All are adult males with vocal slits and nuptial pads. SVL ranges from 36.1–41.8 mm. SAMA R71762 is very similar to the holotype in both morphology and colour pattern ( Table 1 ; Figs 1 , 3 ) but paratype PNGNM differs from them both in having longer limbs (TL/SVL 0.65 vs. 0.54–0.58; compare Figs 1A–C ), a wider head (HW/SVL 0.36 vs. 0.32 for both other types), and a lower EN/IN ratio (0.59 vs. 0.64–0.67). This paratype also has a colour pattern that differs dramatically in life from the other two specimens, comprising a mid-brown dorsum covered with extensive small dark-brown flecks with no trace of any green pigmentation ( Fig. 1C ). However, extensive variation in colour pattern is common among torrent-breeding pelodryadid frogs (e.g. Tyler 1968; Oliver et al. 2024; and see Fig. 4 ) and in its overall body form and snout shape the PNGNM paratype closely resembles the other two types. The co-occurrence of these three specimens on a single waterfall at a high-montane stream where no other pelodryadids were observed also suggests that the observed differences reflect variation within a single species. Future collections including genetic material may necessitate a reassessment of this conclusion.

Comparisons with other species. High-elevation treefrog communities in New Guinea are dominated by a radiation of torrent-dwelling Litoria that appears to be monophyletic ( Oliver et al. 2024). Unfortunately, genetic samples were not taken from the type series of Litoria stellarum sp. nov. so we were unable to generate sequence data to confirm its phylogenetic associations. However, based on its size, acuminate snout shape, reduced webbing on hands, and ecology, we are confident that the new species is part of this radiation of stream-breeding Litoria , and we here focus comparisons against other species in this group.

Litoria stellarum sp. nov. is substantially larger (min adult male SVL> 35 mm versus max adult male SVL <30 mm) than L. amnicola Richards, Tjaturadi, Krey & Donnellan, 2021 , L. brongersmai ( Loveridge, 1945) , L. fuscula Oliver & Richards 2007 , L. grinpela Richards and Oliver, 2024 , L. lakekamu Richards & Bickford, 2023 , L. leucova ( Tyler, 1968) , L. megalops Richards & Iskandar, 2006 , L. modica ( Tyler, 1968) , L. napaea ( Tyler, 1968) , L. rara Günther & Richards, 2005 , L. rivicola Günther & Richards, 2005 and L. scabra Günther & Richards, 2005 . Litoria stellarum sp. nov. is substantially smaller than L. angiana ( Boulenger, 1915) and L. skeliphros Oliver, McDonald, Dahl, Nagombi & Richards, 2024 (max male SVL <45 mm versus> 50 mm), and further differs in having hands webbed between fingers 3–4 only (versus webbed between all digits).

Litoria stellarum sp. nov. can be distinguished from similar-sized (male SVL between 30–45 mm) species of torrent-dwelling Litoria as follows: from L. arfakiana ( Peters & Doria, 1878) , L. macki Richards, 2001 , L. oenicolen Menzies & Zweifel, 1974 , L. spinifera ( Tyler 1968) and L. wollastoni ( Boulenger, 1914) by lacking (versus having) one or more prominent conical tubercles on the heel. It further differs from L. arfakiana , L. macki and L. spinifera by having thick fleshy basal webbing between fingers 3–4 ( Fig. 2C ; versus at most a trace of thin membranous webbing), and further from L. oenicolen by its basal finger webbing (versus fingers ~1/3 webbed) and from L. wollastoni by its reduced toe webbing (~3/4 webbed versus web between toes extending to discs on outside of Toe 3 and inside of Toe 5 (cf. Fig. 2D )). It differs from L. micromembrana ( Tyler 1968) and L. bulmeri ( Tyler 1968) in its distinctly different snout shape (acuminate versus rounded in lateral profile) and in having (versus lacking) webbing between Fingers 3–4, and further from L. bulmeri by having brown base colouration and lacking a welldefined black lateral stripe (versus green dorsum and black lateral stripe present). The new species differs from L. dorsivena ( Tyler, 1968) and L. hastula Oliver, Iskandar & Richards, 2023 by its rounded snout in dorsal profile (versus moderately to sharply acuminate), webbing on fingers basal (versus moderately extensive webbing that extends to the third phalanx on Fingers 2, 3 and 4, and larger size in males (SVL> 35 mm v <35 mm); it differs from Litoria kikori Richards & Oliver, 2024 and Litoria spartacus Richards & Oliver, 2006 in having webbing between fingers thick and basal (versus moderately extensive thin webbing extending to third phalanx on Fingers 2, 3 and 4), snout rounded in dorsal profile and acuminate in lateral profile (versus weakly acuminate in dorsal profile and rounded in lateral profile), and dorsal colour pattern of brown with or without large pale green blotches (versus green intricately mottled with brown).

Litoria stellarum sp. nov. is most similar in size, colouration, extent and thickness of webbing, and in habitat type, to L. becki , a species known to occur at high elevations from Mt Wilhelm in the east to as far west as the Muller Range ( Fig. 5 ) and which shows extensive variation in colour pattern, even at a single site ( Fig. 4 ). Litoria stellarum sp. nov. can be distinguished from that species by having vocal slits in adult males (versus absent), an acuminate snout in lateral profile (versus rounded), and a near-straight supratympanic fold (versus strongly curved) ( Fig. 6 ).

Distribution and ecology. Litoria stellarum sp. nov. is known only from the type locality, Dokfuma Meadow on the southern slopes of Mount Capella in the Star Mountains, near the Indonesian border on Papua New Guinea’s Central Cordillera ( Fig. 5 ). Similar habitat linked by continuous high elevation areas above 3,000 m a.s.l. is present in nearby areas of Indonesian New Guinea, suggesting this species may not be restricted to Papua New Guinea.

The type locality is in the headwaters of the Ok Tedi River, a region that is extremely steep and rugged ( Fig. 7A ) ( Hyndman & Menzies 1990). Dokfuma is an open, boggy meadow on karst terrain located at 3,200 m a.s.l. that is dominated by low, dense Blechnum ferns and herbs with scattered Cyathea tree ferns. Large moss mounds between about 1–2 m in diameter are scattered across the landscape and the higher perimeter of the meadow is bordered by low, wet mossy alpine forest ( Fig. 7B , and described in detail in Gregory & Johnston (1993)). The type series of Litoria stellarum sp. nov. was collected during the day from under stones in the splash zone of a small waterfall ( Fig. 7C ). We were unable to visit the waterfall at night due to the risk of serious injury from falling into hidden sinkholes. The stream feeding the waterfall emerged from the karst approximately 100 m upstream and disappeared into the karst less than 5 m below the waterfall. The stream could be heard flowing beneath the meadow surface for some distance upstream of its emergence above the waterfall. Temperatures recorded during fieldwork in Dokfuma meadow ranged between 1–18°C ( Gregory & Johnston 1993), suggesting that this new species is adapted to cold conditions.

No other pelodryadid frogs were encountered at this site, but two microhylid frogs, Oreophryne geminus Zweifel, Cogger & Richards 2005 and O. terrestris Zweifel, Cogger & Richards 2005 , both known only from Dokfuma, were common in the meadow fernlands.

Litoria stellarum sp. nov. was not encountered during a five day survey at Minnie Camp (5.0764°S, 141.1514°E) just 7 km southeast of Dokfuma at an altitude of 2,400 m a.s.l. (Richards 2015), nor during a short (two day) survey of a small stream near the summit of Mt Binnie (5.2001°S, 141.1255°E), 20 km south of Dokfuma at 2,200 m a.s.l. where only L. modica was encountered (Richards & Johnston, unpublished data). It was also not encountered in forest on Mt Akrik (5.1597°S, 141.1665°E) 16 km southeast of Dokfuma at the lower elevation of 1,600 m a.s.l, where the following torrent-dwelling pelodrydadid species were encountered: Litoria angiana , L. micromembrana , L. modica and Nyctimystes oktediensis Richards and Johnston 1993 .

IUCN Red List status. Litoria stellarum sp. nov. is known from high elevations on Papua New Guinea’s Central Cordillera in an area where direct human impact is low ( Hope 2014). Assuming it is largely restricted to elevations above 3,000 m a.s.l. (as appears to be the case for the potentially related species L. becki ) the estimated area of continuous suitable habitat around the type locality is around 100 km 2. As a high elevation species with a potentially restricted range the impacts of anthropogenic climate warming are of concern. However, this species’ ecology and distribution are largely unknown. Although we accept that this species may in future require an IUCN Red List status of Vulnerable, we suggest that it be listed as Data Deficient because, although a threat is plausible, it is not confirmed and a fuller understanding of this species’ ecology, elevational range and potential threats is needed to estimate its conservation status with greater confidence.

Etymology. stellarum is a Latin genitive plural of Stella (star), meaning of the stars, referring to this species’ only known locality high in Papua New Guinea’s Star Mountains.

Figures

FIGURE 1. Images of Litoria stellarum sp. nov. in life: A) SAMA R71763 (holotype); B) SAMA R71762 (paratype); C) PNGNM (USNM [SJR]209376) (paratype). All photographs by S. Richards.

FIGURE 2. Details of preserved holotype (SAMA R71763) of Litoria stellarum sp. nov.: A) dorsal view of head; B) lateral view of head; C) ventral view of hand; D) ventral view of foot. Scale bar for images A and B = 5 mm, scale bar for C and D = 2 mm.

FIGURE 3. Preserved type series of Litoria stellarum sp. nov. in A) dorsal view and B) ventral view, from left to right SAMA R71763 (holotype), PNGNM (USNM209376; paratype) and SAMA R71762 (paratype).

FIGURE 4. Images of Litoria becki in life illustrating the extensive colour variation in that species: A) SAMA R65169, B) SAMA R65172, C) SAMA R65168, all males from Muller Range, Western Province, Papua New Guinea; and D) SAMA R71756), male from Gigira Ridge, Hela Province, Papua New Guinea. All photographs by S. Richards.

FIGURE 5. Map showing the type and only known locality for Litoria stellarum sp. nov. (yellow square) and localities for morphologically and genetically confirmed specimens of the similar L. becki (blue circles). The blue arrow indicates the type locality of L. becki. There are additional specimens referred to Litoria becki in museum collections that we have not examined, but this species has historically been confused with other torrent-breeding Litoria so we do not include these records on this map.

FIGURE 6. Comparison of snout and head shape in Litoria stellarum sp. nov. (holotype) (A) and L. becki (B) (SAMA R65167). Note the near-straight supratympanic fold of the new species (versus strongly curved in L. becki), indicated by arrows, and the more acuminate snout in the new species.

FIGURE 7. Landscape and habitat at and around the type locality of Litoria stellarum sp. nov.: A) view of rugged karst ranges in the Star Mountains from the south. Dokfuma Meadow abuts the northern (far) slope of the peak indicated by the arrow; B) alpine meadow habitat at Dokfuma Meadow with Mount Capella in the background; C) waterfall on a short reach of stream that emerges from the karst for approximately one hundred metres; the types of the new species were collected from under stones at the base of this waterfall during the day. All photographs by S. Richards.