Xenorhina perexigua, Günther & Richards, 2021

Guenther, Rainer & Richards, Stephen, 2021, Description of six new species of Xenorhina Peters, 1863 from southern Papua New Guinea (Amphibia, Anura, Microhylidae), Zoosystematics and Evolution 97 (2), pp. 355-382 : 355

Xenorhina perexigua sp. nov.

Holotype.

SAMA R71645 (SJR 10418), adult male, from Camp 2, upper Strickland River basin, Western Province, Papua New Guinea (5.9018°S, 142.4360°E; 950 m a.s.l.), collected by S.J. Richards on 20-02-2008

Diagnosis.

This species of Xenorhina is characterised by the unique combination of: very small body size (SUL of the only adult male 16.7 mm); vomeropalatines each with a single triangular spike; legs moderately long (TL/SUL 0.46); all fingers and first toe without and toes 2-5 with expanded discs; eye-naris distance greater than internarial distance (END/IND 1.27); tympanum smaller than eye (TyD/ED 0.77); dorsal surfaces in life beige brown (RAL 8024) with darker areas on upper flanks, in middle of back and on neck; lower flanks with whitish spots and reticulations and some irregular dark brown flecks; supratympanic area with dark brown fleck; ventral surfaces off-white with extensive blackish-brown reticulation. Advertisement calls in series containing about 30 soft “popping” calls of 30-40 ms duration, produced at a rate of 6.8-6.9 calls/s.

Description of the holotype.

Measurements and ratios are presented in Table 2 . Body squat (Fig. 4a and b ), head broader than long (HL/HW 0.84); snout strongly acuminate from above and below and protruding in profile; tongue broad, only its lateral and posterior edges free; prepharyngeal ridge without denticles; a single triangular spike of moderate size on each vomeropalatine; loreal region oblique, no canthus rostralis; nostrils near tip of snout, directed dorsolaterally, visible from above, but not from below; eye-naris distance greater than internarial distance (END/IND 1.27); greater part of tympanum visible in life and preservative, its diameter smaller than that of eye (TyD/ED 0.77); supratympanic fold short, not contacting posterior edge of eye and not reaching insertion of fore leg; shank of moderate length (TL/SUL 0.46); fingers moderately short, not webbed; tips of fingers not wider than penultimate phalanges, all with circum-marginal grooves that extend along entire length of digits, relative lengths of fingers 3 > 4 > 2 = 1 (Fig. 4c ); all toe tips with circum-marginal grooves, all tips, except that of toe 1 wider than penultimate phalanges; toes not webbed, relative lengths 4 > 3 > 5 > 2 > 1 (Fig. 4d ); plantar and palmar tubercles (with exception of small, but prominent inner metatarsal tubercle), as well as subarticular tubercles scarcely visible. Dorsal surfaces with only a few tubercles and a raised mid-dorsal ridge, ventral surfaces smooth (Fig. 4b ).

In life, dorsal surfaces beige brown with darker areas on upper flanks, in middle of back and in scapular region (Fig. 4a ); lower flanks with whitish spots and whitish reticulations and three (left side of body) or four (right side of body) irregular dark brown flecks which merge with dark brown reticulum of abdomen; supratympanic area with conspicuous dark brown fleck; all ventral surfaces light grey with dense dark brown reticulations (Fig. 4b ); lumbar spot absent; vent and adjacent areas of thighs enclosed in large, triangular dark brown patch, borders of which disintegrate ventrally; outer margin of iris blackish, inner margin golden.

In preservative, dorsal surfaces reddish-brown, flanks with dark irregular spots and supratympanic region with large, dark brown fleck; ventral surfaces ivory-white with brown beige (RAL 1011) reticulum; large ivory-white area between eye and insertion of fore-leg present (not evident in life).

Distribution and ecological notes.

Xenorhina perexigua sp. nov. is known only from one locality, in hill forest at an altitude of 950 m a.s.l. in the upper Strickland River basin of south-western Papua New Guinea (Fig. 8 ). The holotype was calling from within leaf litter on the forest floor at night during rain.

Vocalisation.

Two call series, produced by the holotype ( SAMA R71645) at an air temperature of 21.2 °C, were analysed. Each call is a single soft, unpulsed “pop” note uttered in rapid succession (Fig. 5a ). The two series lasted 4.1 s and 4.5 s and contained 28 and 31 calls produced at a rate of 6.8 and 6.9 calls/s. Call length 29-42 ms (mean 34.6 ± 3.6 ms, n = 59) and inter-call interval 101-195 ms (mean 115.0 ± 17.1 ms, n = 57). While calls are of approximately equal length throughout each series, inter-call intervals are slightly longer at the end of call series than at the beginning. Volume of calls increases during course of series, as is typical for many Xenorhina species. Calls start abruptly at high amplitude, which then decreases at an irregular rate until the end of each call (Fig. 5a ). The start of each call also has a broad frequency range that drops rapidly to a more narrowly defined, frequency-modulated band (Fig. 5b ). Fundamental and dominant frequency peak at 1.4 kHz (Fig. 5c ).

Etymology.

The specific epithet Xenorhina perexigua is a Latin adjective of feminine gender, meaning very small (translation of perexiguus, -a, -um in the Dictionarium latino-germanicum means "sehr klein") and refers to the diminutive size of the new species.

Comparisons with other species.

Although this species is represented by only a single specimen, it is an adult male of very small size (16.7 SUL mm) and, given knowledge about the size ranges of congeners, its SUL is unlikely to exceed 25 mm. We, therefore, compare Xenorhina perexigua sp. nov. with all congeners of a similar size (SUL 15-25 mm) that have a single spike on each vomeropalatine.

Xenorhina anorbis (Blum & Menzies, 1989) is larger (holotype is an adult male with SVL of 21.3 mm [range of type series 21.3-23.4 mm but sex of other specimens not specified] vs. SUL 16.7 mm in one male), has hind legs shorter (TL/SVL < 0.38 vs. > 0.38) and discs of fingers and toes not wider than penultimate phalanges (vs. discs on toes 2-5 clearly wider than penultimate phalanges in Xenorhina perexigua sp. nov.).

Xenorhina brachyrhyncha Kraus, 2011 appears to be larger (two adult females with SVL 21.2 and 22.8 mm vs. SUL 16.7 mm in one male), with snout blunt in dorsal and ventral view (vs. strongly acuminate), head wider and longer (HW/SVL 0.35-0.38 vs. 0.32 and HL/SVL 0.30-0.32 vs. 0.28) with much lower ratio of eye-naris distance to internarial distance (END/IND 1.06-1.13 in X. brachyrhyncha vs. 1.27 in Xenorhina perexigua sp. nov.); differences in colour include lack of a dark supratympanic spot in X. brachyrhyncha (vs. present in Xenorhina perexigua sp. nov.) and less pronounced dark reticulation on all ventral surfaces.

Xenorhina lanthanites is larger SUL 21.3-22.4 mm vs. SUL 16.7 mm), with tips of toes wider than penultimate phalanges only on 4th toe (vs. toes 2-5 with expanded terminal discs); ratio of END/IND lower (0.94-1.20 vs. 1.27); and advertisement call series much longer, lasting up to more than one minute (vs. < 5 s) with average call length of 121 ms (vs. 35 ms in Xenorhina perexigua sp. nov.), dominant frequency of about 1.0 kHz (vs. 1.4 kHz) and call repetition rate of 1-2 calls/s (vs. 6.8-6.9 calls/s).

Although it is known from just one specimen, it is an adult male suggesting that Xenorhina perexigua sp. nov. is amongst the smallest known members of the genus. Only one other species, X. bouwensi , may be smaller than Xenorhina perexigua sp. nov., but it can be immediately distinguished from the new species by its lacking odontoid spikes on the vomeropalatines.

Figures

Figure 4. Holotype (SAMA R 71645) of Xenorhina perexigua sp. nov. in life: (a) Dorsolateral view; (b) Ventral view; (c) Volar view of right hand; (d) Thenar view of right foot.

Figure 5. (a) Oscillogram and (b) Spectrogram of the last six calls of a call series containing 31 calls from the holotype of Xenorhina perexigua sp. nov.; (c) Amplitude spectrum of an advertisement call from the holotype of X. perexigua sp. nov.

Figure 8. Map of Papua New Guinea showing the known distributions of X. lacrimosa sp. nov. (blue circles), X. perexigua sp. nov. (yellow triangle) and X. pohleorum sp. nov. (red squares). Arrows indicate the type localities.