Choerophryne koeypad, Hoskin, 2025

Choerophryne koeypad sp. nov.

Koeypad Frog

( Figures 7–9 View FIGURE 7 View FIGURE 8 View FIGURE 9 )

Material examined. Holotype ( Fig. 7 View FIGURE 7 ). QM J98929 View Materials , field number conx5944, male, calling when captured, Dauan Island ( 9.4227° S, 142.5301° E), 13 January 2021, C. J. Hoskin, K. Aland, A. Davies, A. Zwar GoogleMaps . Paratypes. QM J98930 View Materials , QM J98931 View Materials , QM J98932 View Materials (field numbers conx5945, conx5946, conx5947, respectively) , all calling males. Collection details as for holotype.

Diagnosis. A relatively large (males 20.0– 21.2 mm), short–snouted (SN/ SVL 0.13–0.14) Choerophryne species, with a hidden tympanum in males, relatively short hindlimbs (TL–knee/ SVL 0.39–0.42), relatively short hands (HandL/ SVL 0.22–0.25) and feet (FootL/ SVL 00.31–0.33), relatively smooth dorsal skin, and call a regularly repeated (call interval 1.0– 2.5 s) burst of ‘tinks’ of relatively short call duration (0.78– 3.17 s), moderate note rate (6.13–6.94 notes/s) and relatively low frequency (dominant frequency 2885–3092 Hz) .

Description of type series. Measurements and proportions of the type series are presented in Table 1. A moderately large Choerophryne (male SVL mean 20.8 mm, range 20.0– 21.2 mm). Head relatively wide (HW/SVL 0.34–0.38); broadly triangular in dorsal view, with a relatively short snout (SN/SVL 0.13–0.14); canthus rostralis rounded; loreal region steeply oblique, almost vertical, slightly concave posterior to naris; nostrils round, directed laterally, much closer to tip of snout than to eyes; tip of snout broad (IN/SVL 0.064 –0.072); internarial distance less than distance from naris to eye (EN/IN 1.33–1.46); snout generally slightly projecting (overhung) in lateral view (but no projection in QM J98929 View Materials ), truncate in dorsal view; eyes moderately large (EYE/SVL 0.10–0.12; EYE/SN 0.71–0.85); tympanum completely hidden by skin; no supratympanic fold. Moderately long forearm, hand and 3 rd finger (ArmL/SVL 0.45–0.50; FA/SVL 0.23–0.25; HandL/SVL 0.22–0.25; F3L/SVL 0.14–0.15). Relative length of fingers 3>4>2>1; fingers unwebbed, but thickened skin gives the appearance of basal ‘webbing’ between fingers 2–3 and 3–4; large discs present on all fingers, about three times the width of penultimate phalanges (except the disc on finger 1, which is about two times wider); disc largest on 3 rd finger (3FD/SVL 0.049 –0.070), smallest on 1 st finger (1FD/SVL 0.028 –0.039); discs on all fingers truncate, especially on fingers 2, 3 and 4, where the discs are ‘T-shaped’ with a slight indentation at the midpoint of the distalmost edge; circum-marginal grooves present on all finger discs but generally hard to discern (perhaps an artefact of preservation), and particularly indistinct on finger 4; subarticular tubercles present, obvious near base of fingers 1 and 2 and about halfway along fingers 3 and 4, and second, smaller, tubercle usually present near distal end of each finger; metacarpal tubercles absent, but thickened, unpigmented skin present along base of palm. Hindlimb, foot and 4 th toe relatively long (TL–knee/SVL 0.39–0.42; FootL/SVL 0.31–0.33; T4L/SVL 0.16–0.19). Relative length of toes 4>5≥3>2>1; toes unwebbed (but QM J98932 View Materials has thickened skin between base of toes 3–4 and 4–5); discs present on all toes, about twice width of penultimate phalanges (except disc on toe 1, which is about 1.5 times); disc widest on toe 4 (4TD/SVL 0.034 –0.058), narrowest on toe 1 (1TD/SVL 0.033 –0.047); toe discs smaller than those of fingers (3FD/4TD 1.08–1.52); rounded to moderately truncate, especially on toes 2, 3, 4 and 5; all discs with well–developed circum-marginal grooves; one subarticular tubercle on each toe, about halfway along, but some indication of a second tubercle on toe 4; a small, low, elongate, inner metatarsal tubercle; outer metatarsal tubercle absent. Skin texture in preservative. Dorsal texture smooth or very finely granular or dimpled ( Fig. 7 View FIGURE 7 ). Lateral surfaces smooth. Ventral surfaces smooth but with very fine granular texture on vocal sac (e.g., Fig. 8F View FIGURE 8 ). Colouration in preservative (e.g., Figs 7 View FIGURE 7 , 8F View FIGURE 8 ). Dorsal body and head pale beige ground colour with irregular, dark brown blotches; on closer inspection (under magnification) dorsal surface light brown (QM J98929 View Materials and QM J98930 View Materials ) or light grey (QM J98931 View Materials , QM J98932 View Materials ), heavily patterned with dark brown blotching due to areas of dense stippling (remaining surfaces lightly stippled). Dorsal surfaces of all limbs (including hands and feet) as for head and back but paler. Dark grey along upper loreal area, between naris and eye; some indication of a thin, pale beige midline streak along top of snout and head (continuing as a vertebral line down the back), and pale beige interorbital bar (pale markings on head more conspicuous on two paler frogs: QM J98931 View Materials and QM J98932 View Materials ). Lateral surfaces cream or white, heavily stippled with brown or black. Ventral surfaces ( Fig. 8F View FIGURE 8 ) cream or white, with very fine brown or black stippling on all surfaces, most prominent on throat and chest and under forearms; palmar and plantar surfaces pale grey with scattered fine black stippling, white subarticular tubercles and areas of thickened white skin at base of palm and heel. Pupil horizontal (but usually dilated).

Colour pattern and skin texture in life. Adult males (e.g., Fig. 8A–E View FIGURE 8 ). Dorsal ground colour light brown/ straw, with dark brown mottling or blotching. In some individuals blotching on back, shoulders and head connected to form extensive, irregular dark area down back, from between eyes to lumbar region. Most individuals with indication of pale beige interorbital bar and a thin, pale beige vertebral line extending from snout down length of back to urostyle, but these pale beige markings interrupted by darker markings. Dark brown band along upper canthal area, from naris to eye, continuing behind eye as an irregular band of irregular dark lateral markings above forelimb to groin. Dorsal colour and pattern of limbs, feet, hands and digits, as for head and back but typically paler (e.g., Fig. 8B, 8E View FIGURE 8 ). Posterior thigh light grey, extending as light grey blotches onto top of thigh, with some straw-coloured markings ( Fig. 8B View FIGURE 8 ). Ventral surfaces pale pinkish grey, with small white spots and blotches on chest and throat. Underside of limbs, feet, hands and digits also pale pinkish grey, with small white spots on trailing edge of underside of thighs, and subarticular tubercles and discs white. Dorsal skin texture finely granular, with all dorsal surfaces evenly covered in small, rounded pustules and fine pitting. Ventral surfaces smooth. Females and subadults. Unknown.

Call. Each call is a short series of high-pitched notes: “tink, tink, tink, tink, …” ( Fig. 9 View FIGURE 9 ). Males call incessantly, with calls uttered in quick succession (interval between calls is about the same as call duration). Call measures are presented in Table 2, and have the following average values (with range in parentheses): call duration 1.65 s (0.78–3.17); number of notes 10.0 (5–19), note rate 6.38 notes/s (6.13–6.94); dominant frequency, one clear peak in energy, 2997 Hz (2885–3092); note length 0.0504 s ( 0.045 –0.059); note interval 0.134 s ( 0.110 –0.155); call repetition rate 1.65 s (1.00–2.49).

Comparisons. The combination of short snout (i.e., not obviously elongated), hidden or inconspicuous tympanum, and call that is a burst of ‘tinks’ distinguishes C. koeypad sp. nov. from all congeners except C. exclamitans and C. crucifer Günther & Richards, 2017 .

Choerophryne koeypad sp. nov. is most similar to C. exclamitans View in CoL , with which is shares a hidden tympanum in males and a metallic, tinking call. Choerophryne koeypad sp. nov. differs from C. exclamitans View in CoL in the following morphological traits: larger size (adult male SVL mean 20.8 mm, range 20.0–21.2 vs mean 17.1 mm, 15.3–20.6); shorter hand (HandL/SVL mean 0.24, 0.22–0.25 vs 0.26, 0.25–0.29); shorter foot (FootL/SVL mean 0.32, 0.31–0.33 vs 0.35, 0.33–0.38); dorsal surfaces smooth to finely granular ( vs more rugose, with scattered larger tubercles); ventral colour in preservative pale cream (e.g., Fig. 8F View FIGURE 8 ) ( vs “overall uniformly dark gray” Kraus & Allison 2005a), and ventral colour in life pale pinkish grey with scattered small white spots ( vs “peppered light gray on a dark gray background” Kraus & Allison 2005a). The call of C. koeypad sp. nov. differs from that of C. exclamitans View in CoL in being shorter (mean 1.65 s, 0.78–3.17 vs 4.7 s, 0.32–6.75); having fewer notes (mean 10, 5–19 vs 35, 3–48), slower note rate (mean 6.15 notes/s, 5.81–6.41 vs 7.6 notes/s, 6.5–9.4; calculated here as number of notes divided by entire call duration, to match Kraus & Allison (2005a)); lower dominant frequency (mean 2997 Hz, 2885–3092 vs 3400 Hz, 3256–3480); longer note length (mean 50 ms vs 20 ms); and much faster call rate (average interval between calls 1.7 s vs 18 s).

Choerophryne koeypad sp. nov. differs from C. crucifer View in CoL (which also has a short snout, an inconspicuous tympanum, and a tinking call) in being substantially larger (adult male SVL 20.0– 21.2 mm vs 13.4–17.3 mm); having the tympanum completely hidden ( vs small, about one-third of eye diameter); and in having a call of higher note rate (6.13–6.94 notes/s vs 4.39–5.18 notes/s) and much lower dominant frequency (mean 2997 Hz vs 5500 Hz). Data for C. crucifer View in CoL comes from Günther & Richards (2017).

Etymology. The species name koeypad is derived from the local language (Kalaw Kawaw Ya) words “koey pad”, meaning rocky mountain, and refers to the species being restricted to boulder habitat on Simakal Pad (Mt Cornwallis). Local language was provided by Laurie Elisala, Torenzo Elisala, Abi Mooka, Tenny Elisala, and Thomas Mooka.

Distribution. Only known from Dauan Island ( Fig. 10 View FIGURE 10 ). Likely to be endemic to the island, based on the lack of piled boulder habitat on nearby islands or the adjacent New Guinean mainland. All records come from the lower to mid slopes of Mt Cornwallis (Simakal Pad), from about 40–150 m a.s.l., but no surveys were conducted above this elevation.

Natural history. Restricted to areas of deeply piled granite boulders with associated rainforest vegetation ( Fig. 6 View FIGURE 6 ). Males were most commonly found calling from the upper surface of green leaves of vines and other vegetation growing amongst the boulders, in the range of 50 cm to 2.5 m above the surface rocks. Several males were calling from the vertical faces of large surface boulders, and one male was calling from below surface level in piled boulders. Females and subadults were not found. Choerophryne koeypad sp. nov. was only found in direct association with piled boulders, and surveys away from piled rock did not find the species. Our survey, on the western side of Mt Cornwallis (Simakal Pad), found lower density and more patchy occurrence of males at lower elevations and more uniform occurrence and higher density towards mid elevation on the mountain. No surveys were conducted at higher elevations (i.e.,> 150 m a.s.l. to the summit at 290 m a.s.l.). Surveys were conducted during wet weather, and it is assumed this species retreats among boulders during dry periods. There is no information on breeding biology but C. koeypad sp. nov. is assumed to be a terrestrial breeder with direct development, as for other asterophryines (e.g., Hoskin 2004; Anstis et al. 2011).

Conservation. Assuming C. koeypad sp. nov. is restricted to Dauan Island, it has a very small distribution. The area of potentially suitable boulder-field habitat is estimated as 1 km 2 (or 1.05 km 2 measured as a minimum convex polygon), but patchy occurrence in the survey to date suggests the species is unlikely to occur in all of that area. Choerophryne koeypad sp. nov. fits an IUCN listing of Vulnerable (Criterion D2) based on the following. It has an area of occupancy well below the threshold of 20 km 2 and occurs at a single location (as defined by ‘a single threatening event could rapidly affect all individuals’; IUCN 2024), with a plausible future threat (Yellow Crazy Ants) that could rapidly drive the species to Critically Endangered or Extinct (as covered above for C. gobakula sp. nov.). More detailed surveys are required to estimate fine-scale distribution on Dauan Island, and to assess other potential threats.