Amolops sengae, Sheridan & Phimmachak & Sivongxay & Stuart, 2023

Sheridan, Jennifer A., Phimmachak, Somphouthone, Sivongxay, Niane & Stuart, Bryan L., 2023, Systematics of the Lao torrent frog, Amolops cremnobatus Inger & Kottelat, 1998 (Anura: Ranidae), with descriptions of four new species, Vertebrate Zoology 73, pp. 931-956 : 931

Amolops sengae sp. nov.

Figure 10 "Clade C"

Chresonymy. Amolops cremnobatus Stuart (2005: 476, part), Stuart et al. (2010: 57), Stuart et al. (2013: 102), Wu et al. (2020: 5, part).

Holotype.

NCSM 79424 (field number BLS 15273), adult male, Laos, Xaignabouli Province, Paklay District, Pak Maat, 18.82588°N, 101.84090°E, 242 m elev., coll. 1942h on wet rock face above chute in 1-2 m wide steep rocky stream in disturbed semi-evergreen forest on 25 March 2012 by Bryan L. Stuart, Sengvilay Seateun, and Khampong Thanonkeo.

Paratypes.

Laos, Vientiane Province, Kasi District, Ban Namon: FMNH 258376-77 (two adult females), 19.07750°N, 102.14556°E, 200-300 m elev., coll. 1 September 1999 by Michael Baltzer. - Laos, Xaignabouli Province, Paklay District, Pak Maat: NCSM 79417, NCSM 79422-23, NUOL 00032 (four adult males), same data as holotype.

Referred larvae.

Laos, Vientiane Province, Feuang District, Ban Naxeng, Houay Kang Thang: NUOL 01596 (five larvae), 18.86951°N, 102.12005°E, 410 m elev., coll. 17 December 2014 by Fongfany Libounyasao.

Etymology.

The specific epithet is a matronym for Sengvilay ( “Seng”) Seateun of the National University of Laos, co-collector of much of the new material described here, major contributor to the herpetology of Laos, native of Xaignabouli Province that is home to the type locality of the new species, and cherished friend and colleague of the authors.

Suggested Common Names.

Seng’s Lao torrent frog (English), ຂຽດເກາະຜາລາວແສງ (Khiat Korpha Lao Seng; Lao).

Diagnosis.

A member of the Amolops larutensis group having the combination of 2-3 vomerine teeth, sometimes faint or absent; relative finger lengths I <IV<II <III; spinose glands above the arm absent; mean ± SE SVL of adult males 29.8 ± 1.5 mm (range 27.2-31.2 mm; n = 5) and of females 39.2-39.6 mm (n = 2); SNT 4.9 ± 0.3 mm (range 4.4-5.2 mm) in males and 5.2-5.8 mm in females; FTL 14.3 ± 0.7 mm (range 13.1-15.1 mm) in males and 18.4-19.1 mm in females; HND 8.7 ± 0.9 mm (range 7.3-9.6 mm) in males and 11.8-12.0 mm in females; and SHK 17.7 ± 0.9 mm (range 16.2-18.4 mm) in males and 24.0-24.5 mm in females.

Description of holotype.

Habitus moderately slender. Head width approximately equal to head length. Snout weakly pointed in dorsal view. Snout projecting slightly beyond lower jar in lateral view, sloping obliquely back to lip. Nostril lateral, nearer to tip of snout than to eye. Canthus rostralis distinct. Lores oblique and slightly concave. Eye diameter sub-equal to snout. Pineal body present. Tympanum distinct, round, roughly one-third eye diameter, slightly depressed relative to skin of temporal region. Rictal glands very small and round. Vomerine teeth obliquely angled, closer to each other than to choanae, and extremely small and indistinct. Tongue cordiform notched posteriorly. Vocal slit opening near corner of jaw. No gular pouch, but extra skin at corners of lower jaw.

Forelimb moderately slender. Tips of all four fingers expanded into wide discs, with circummarginal grooves. Fingers slender. Relative finger lengths I<IV<II<III. No webbing on hands. Subarticular tubercles conspicuous, surfaces rounded, formula 1, 1, 2, 2. One supernumary tubercle at base of fingers 2-4. Irregular palmar tubercle. Well-developed nuptial pad on Finger I, on dorsal surface to level of distal end of subarticular tubercle.

Hindlimbs moderately long and slender. Toes slender. Tips of toes expanded into wide discs, with circummarginal grooves. Web on all toes to base of disc. Outermost toe disc small, barely wider than finger. Widest toe disc narrower than all finger discs except for that of thumb. Subarticular tubercles conspicuous, surfaces rounded; formula 1, 1, 2, 2, 2. Inner metatarsal tubercle oval; outer metatarsal tubercle small, round.

Dorsal skin surface glandular and spinose. No supra-tympanic fold. Glandular dorsolateral fold. Flanks with spinose glands at dorsal edge, but no spinose glands above arm. Glands surrounding vent. Ventral surface slightly glandular.

Measurements of holotype (mm): SVL 30.1, HDL 10.7, HDW 10.9, SNT 4.8, EYE 4.5, IOD 3.0, IND 3.4, TMP 1.6, TEY 0.8, SHK 17.5, TGH 16.5, HND 8.7, FTL 14.4.

Coloration.

In preservative, dorsal coloration very dark brown-black with minimal beige spotting. Pale bars on dorsal surface of thighs and some pale spots on arms, but no distinct bars. Posterior surface of thighs smooth and dark with some light beige coloration. Ventral surfaces creamy beige, but with some dark veining under chin and along posterior margin of chin. Ventral surface of feet are dark brown to black, and ventral surfaces of hands are dark beige to brown.

In life, dorsal surface greenish-brown with bright green markings. Dorsal surface of legs paler in color than dorsum. Eye mottled gray on lower one-third, mottled yellowish on upper one-third, with orange on anterior and posterior portions. No ventral photos exist for this species in life, but ventral surface of recently euthanized NCSM 79417 shows chin and belly to be bright white with some dark mottling, and underside of arms and thighs to be translucent.

Larvae.

Based on a larva NUOL 01596.2 at S28. Tadpoles are assigned to this species because they were collected at the type locality and their morphology largely agrees with the tadpole description of A. cremnobatus by Inger and Kottelat (1998), including a divided upper jaw sheath and high number of labial tooth rows [9-10(5-9, 5-10)/6(1)]. Tadpoles of A. sengae sp. nov. belong to the exotrophic, lotic, gastromyzophorus larval type ( McDiarmid and Altig 1999), with large oral discs ventrally.

Head-body oval, broadly rounded, wider anteriorly than posteriorly, with weak constriction near line through nares. Body width approximately 60% of BL, widest anterior to eyes. HB flat below with large abdominal sucker. Eyes dorsolateral, pointed laterad. Nares dorsolateral, closer to eyes than tip of snout. Spiracle low on side, tube free of body wall. Tail lanceolate, margins tapering in distal third to narrowly rounded tip; muscle deeper than fins in proximal half. Dorsal fin origin behind HB, origin of ventral fin distal to origin of dorsal fin. HB without spinules. Glands postocular, no glands in fins. Oral disc nearly as wide as head-body, ventral; labial teeth 9-10(4 or 5-10)/6(1). A1 at margin of upper lip, short, approximately one-half length of A2, with very small denticles compared to other tooth rows. A2 approximately two-thirds length of A3. Papillae short, thick, in single row, absent from middle third of upper lip, but present across entire lower lip. Jaw sheaths with outer surface smooth, upper sheath divided, gap between black halves slightly greater than depth of keratinized portions; lower jaw sheath in single piece. Jaw sheaths with fine serrae.

Color in preservative of head-body brown dorsally and laterally, cream ventrally without spots. Caudal muscle brown dorsally and laterally, cream ventrally. Upper fin with melanophores throughout, and lower fin with melanophores in distal half to two-thirds.

Sexual dimorphism.

Males (n = 5) differ from females (n = 2) in being smaller (29.8 ± 1.5 mm SVL vs 39.2-39.6 mm; Table 1 ), possessing an obvious pineal body (indistinct in females), as well as having paired vocal slits and distinct nuptial pads at base of first finger. Dorsal coloration very dark in males, mostly black with very minimal beige spotting or mottling. Females dark brown with beige mottling/reticulation.

Variation.

Pineal body sometimes absent, sometimes present, and seems to be more obvious in males than in females. Rictal glands indistinct in one female (FMNH 258377). Roof of mouth of females is much rougher than that of males. Outer metatarsal tubercle nearly indistinguishable on one female (FMNH 258377). No webbing on hands, but in some males there appears to be very minimal basal webbing. Oval thenar tubercle in females. Outermost toe disc extremely small in all males (about the width of the toe itself) but slightly wider in females. Outer metatarsal tubercle much more difficult to see on FMNH 258377. Dorsal skin of two males (NCSM 79417 and 79422) as well as females glandular but not spinose. Flanks with spinose glands at dorsal edge in individuals that have spinose glands dorsally, all others have glandular skin on flanks without spines. Females dark brown with beige mottling/reticulation. Rear of thighs of females with irregular pale mottling. Females and most males have some dark mottling under chin, and most males have dark mottling on chest, but male NCSM 79422 lacks any dark spots/markings on chin, chest, or belly.

Distribution and natural history.

This species is known from clear streams with torrents from Vientiane Province, Laos westward across the Mekong River into Xaignabouli Province, Laos. A population from Nan Province, Thailand, is provisionally referred to this species.

Comparisons.

Amolops sengae sp. nov. differs from A. cremnobatus , A. tanfuilianae sp. nov., A. kottelati sp. nov., and A. attiguus sp. nov. by lacking spinose glands above the arm (usually present in A. cremnobatus , A. tanfuilianae sp. nov., A. kottelati sp. nov., and A. attiguus sp. nov.). Amolops sengae sp. nov. further differs from A. tanfuilianae sp. nov. and A. kottelati sp. nov. by having a smaller number (2-3) of vomerine teeth (3-4 in A. tanfuilianae sp. nov. and A. kottelati sp. nov.). Amolops sengae sp. nov. further differs from A. tanfuilianae sp. nov. by having males with smaller SVL of 29.8 ± 1.5 (32.2 ± 1.5 in A. tanfuilianae sp. nov.; t-stat 3.3, two-tailed p-value = 0.02). Amolops sengae sp. nov. further differs from A. cremnobatus and A. tanfuilianae sp. nov. by having relative finger lengths I<IV<II<III (I<II<IV<III in A. cremnobatus and A. tanfuilianae sp. nov.). Amolops sengae sp. nov. further differs from A. cremnobatus and A. attiguus sp. nov. by having larger SNT and smaller FTL, and from A. cremnobatus by having smaller SHK (Table 3 ; Fig. 11 ). Amolops sengae sp. nov. further differs from A. tanfuilianae sp. nov. and A. kottelati sp. nov. by having tadpoles with smaller BL. Amolops sengae sp. nov. further differs from A. cremnobatus by having tadpoles with smaller relative ODW and larger relative IP and RND (Table 2 ).

Figures

Figure 10. Amolops sengae sp. nov., NCSM 79417, in life (top row), and NCSM 79424 in preservative (bottom row).

Figure 11. Box and whisker plots of measurements (mm) of morphological features of males of Amolops cremnobatus (B; n = 12), A. sengae sp. nov. (C; n = 5), and A. attiguus sp. nov. (E; n = 5). Measurements are snout-vent length (SVL), snout length (SNT), eye diameter (EYE), tympanum-eye distance (TEY), tarsus length (SHK), and foot length (FTL). Boxes show interquartile range and median (thick black line). Whiskers represent range up to 1.5 x interquartile range (IQR); dots show range beyond 1.5 x IQR. Clusters with the same symbol (* and †) are not significantly different, as determined by paired two-tailed t-tests following ANOVA.