Hidden tribe: A new species of Stream Toad of the genus Ansonia Stoliczka, 1870 (Anura: Bufonidae) from the poorly explored mountainous borderlands of western Thailand Author Suwannapoom, Chatmongkon School of Agriculture and Natural Resources, University of Phayao, Phayao 56000, Thailand Author Grismer, L. Lee Herpetology Laboratory, Department of Biology, La Sierra University, 4500 Riverwalk Parkway, Riverside, California 92505, USA & Department of Herpetology, San Diego Natural History Museum, PO Box 121390, San Diego, California, 92112, USA lgrismer@lasierra.edu Author Pawangkhanant, Parinya School of Agriculture and Natural Resources, University of Phayao, Phayao 56000, Thailand Author Naiduangchan, Mali Rabbit in the Moon Foundation, Suan Phueng, Ratchaburi, Thailand Author Yushchenko, Platon V. Department of Vertebrate Zoology, Biological Faculty, M. V. Lomonosov Moscow State University, Moscow 119234, Russia & Joint Russian-Vietnamese Tropical Research and Technological Center, Nghia Do, Cau Giay, Hanoi, Vietnam Author Arkhipov, Dmitriy V. Department of Vertebrate Zoology, Biological Faculty, M. V. Lomonosov Moscow State University, Moscow 119234, Russia Author Wilkinson, Jeffery A. Department of Herpetology, California Academy of Sciences, 55 Concourse Drive, Golden Gate Park, San Francisco, California 94118, USA & H. T. Harvey & Associates, 938 University Avenue, Bldg. D, Los Gatos, California 95032 Author Poyarkov, Nikolay A. https://orcid.org/0000-0002-7576-2283 Department of Vertebrate Zoology, Biological Faculty, M. V. Lomonosov Moscow State University, Moscow 119234, Russia & Joint Russian-Vietnamese Tropical Research and Technological Center, Nghia Do, Cau Giay, Hanoi, Vietnam n.poyarkov@gmail.com text Vertebrate Zoology 2021 2021-12-03 71 763 779 http://dx.doi.org/10.3897/vz.71.e73529 journal article http://dx.doi.org/10.3897/vz.71.e73529 2625-8498-71-763 82F0310B38FF417BA2B68D8F67AD069D B9707890390A570B80EE5E1EF2ADCF1B Ansonia karen sp. nov. Suggested Common Name: Karen Stream Toad Figures 3 , 4 , 5 , 6 , 7 Holotype. ZMMU A-7605 (field number NAP-06631), an adult male collected on 8 November 2016 at a forest stream within the montane evergreen forest of Khao Laem Mt., Suan Phueng District, Ratchaburi Province, Thailand ( 13.54732N , 099.20394E ; 715 m a.s.l. in elevation), by P. Pawangkhanant, C. Suwannapoom and N. A. Poyarkov. Paratypes (n=15). ZMMU A-7606 (field number NAP-06630), an adult male with same collection information as holotype; ZMMU A-7607 (no field number) and ZMMU A-7608 (field number AUP-00349), two adult males collected on 15 June 2018 at same locality as holotype by P. Pawangkhanant, C. Suwannapoom and M. Naiduangchan; ZMMU A-7609-A-7614 (field numbers NAP-10193-NAP-10198), five adult males and an adult female collected on 18 June 2019 at a forest stream within the montane evergreen forest on the northern slope of Khao Laem Mt., Suan Phueng District, Ratchaburi Province, Thailand (N 13.54581, E 099.20368; 758 m a.s.l. in elevation), by P. Yushchenko and M. Naiduangchan; AUP-00661-00665, two adult males and three adult females collected on 15 June 2019 at same locality as holotype by P. Pawangkhanant and M. Naiduangchan; and ZMMU A-7615 (field number NAP-09901), an adult female collected on 4 October 2019 at same locality as holotype by P. Pawangkhanant. Diagnosis. Ansonia karen sp. nov. is recognized as a member of the genus Ansonia based on the results of the molecular phylogenetic analyses that recover it as the sister species of A. thinthinae (Fig. 2 ) as well as by a combination of the following morphological characters: small body size (maximum SVL 25.6 mm in males and 29.2 mm in females); long slender limbs bearing long slender digits with bulbous tips; absence of parotoid glands; weak subarticular tubercles; and membranous foot webbing ( Inger 1960 , 1966 , 1992 ; Wilkinson et al. 2012 ; Chan et al. 2014 ; Grismer et al. 2016; Quah et al. 2019 ). It can be differentiated from all congeners by the following combination of characters: maximum SVL in males 25.4 mm and females 29.2 mm; snout projecting beyond lower jaw; tympanum visible; no interorbital or tarsal ridges; first finger shorter than second; finger tips bulbous, toe tips slightly dilated forming weak discs; approximately 2.5 phalanges free of web on fourth toe and 0.5 phalanges free of web on fifth toe; yellow rictal tubercles at angle of jaw; distinct, red-tipped, spiny tubercles on dorsum and flanks; abdomen coarsely granular; no oblique flaps of skin bordering vent; wide, light-colored patch below eye; light-colored, generally diamond-shaped interscapular spot; large, discrete, yellow, submandibular spots; no light-colored streaks on canthus rostralis; dorsum black, lacking an X-shaped marking surrounding interscapular spot; no dark-colored markings on rump; no dark dorsolateral stripe; iris yellow-gold; fore- and hind limbs bearing irregularly shaped, light-colored crossbars; venter and undersides of limbs dull-yellow bearing thick, grey-brown reticulations; palmar surfaces of hands and thenar surfaces of feet reddish-orange in life. Description of holotype. Adult male, SVL 24.9 mm (Figs 3 , 4 ); head longer than wide (HL/HW=1.10); snout shorter than wide (SL/SW=0.76), projecting beyond lower jaw, strongly tuberculate, truncate in dorsal view (Fig. 3D ), truncate and sloping in lateral view (Fig. 3C ); canthus rostralis distinct, lores vertical, flat; nares open laterally just below canthus, located much closer to end of snout than to eye (Fig. 3C ); distance between nares smaller than snout length (IND/SL=0.62) and snout width (IND/SW=0.47); eyes large, slightly protruding beyond upper jaws in dorsal view (Fig. 3D ), diameter nearly same as snout length (ED/SL=0.94) and interorbital distance (ED/IOD=1.07); pupils horizontal; interorbital region flat, strongly tuberculate, distance smaller than snout width (IOD/SW=0.67) and snout length (IOD/SL=0.88); tympanum distinct, suboval, taller than wide (Fig. 3C ), horizontal axis less than eye diameter (HTD/ED=0.53); choanae subcircular, separated by a distance larger than their diameter; vomerine ridge and teeth absent; tongue narrow, ending in median point, posterior one-half free. Figure 3. Holotype of Ansonia karen sp. nov. (ZMMU A-7605) from Suan Phueng District, Ratchaburi Province, western Thailand. Photo by N. A. Poyarkov. Forelimbs and fingers long and slender (HAL/SVL=0.30; FLL/SVL=0.69); finger length from shortest to longest: I<II<IV<III; basal webbing not extending beyond proximal subarticular tubercle (Fig. 3E ); fingertips bulbous, slightly dilated but not forming discs; subarticular tubercles indistinct; inner and outer metacarpal tubercles distinct, oval, slightly raised, inner smaller than outer; supernumerary tubercles absent (Fig. 3E ). Hind limbs and toes long and slender (FL/SVL=0.40; HLL/SVL 1.43), toe length from shortest to longest: I<II<V<III<IV; webbing formula: I 0.5-0.5 II 0.5-1 III 0.5-3 IV 2.5-0.5 V; toe tips bulbous, slightly dilated forming weak discs (Fig. 3F ); subarticular tubercles indistinct; inner metatarsal tubercle small, oval, slightly raised; outer metatarsal tubercle raised, rounded, somewhat smaller than inner (OMTL/IMTL=0.72). Upper eyelid, interorbital region, dorsal part of snout and canthus covered with numerous small and larger tubercles; no interorbital ridges; small, randomly arranged tubercles on lores; single row of small spinules on upper lip and outer margin of upper eyelid (Fig. 3C ); four rictal tubercles; no supratympanic folds or parotoid glands; dorsum, flanks, and dorsal surfaces of limbs bearing irregularly spaced, large and small tubercles most of which have brown keratinized spinules, some larger tubercles have more than one spinule; concentration of larger tubercles above tympanum and in scapular region forming an indistinct dorsolateral row extending to insertion of hind limbs; series of brown conical, keratinized tubercles along edges of underside of mandible, absent in gular region (Fig. 3B ); abdomen coarsely granular; all ventral surfaces except for manus and pes covered with coarse, evenly spaced, rounded glandular tubercles. Coloration in life (Figs 3 , 4 ). Top of head black (Fig. 3D ); dorsum and flanks black, punctuated with widely spaced, red-tipped tubercles (Fig. 4 ); dull-yellow, elongate, diamond-shaped insterscapular spot (Fig. 3A ); large, yellowish suborbital patch and rictal tubercles (Figs 3C , 4 ); forelimbs bearing irregularly shaped, light-colored beige-grey bands, most prominent on brachia and extending anteriorly onto shoulder; dorsomedial surfaces of shoulder and digits I and II orangish; gray, irregularly shaped bands on hind limbs; yellow patch on ankles; large, yellow, widely spaced, submandibular blotches confluent with blotch on lower sections of upper lip (Fig. 3B ); gular region light greyish-brown, unicolor; wide, dark-brown, paired, longitudinally oriented pectoral markings grading posteriorly into a wide, black, abdominal reticulum confluent with dark reticulum on ventral surfaces of hind limbs (Fig. 3B ); wide yellow patch surrounding vent extending onto ventral surface of thighs (Fig. 3A ); and bottoms of hands and feet reddish-orange (Fig. 3E-F ). Figure 4. Holotype of Ansonia karen sp. nov. (ZMMU A-7605) in life from Suan Phueng District, Ratchaburi Province, western Thailand. A. Dorsal view. B. Ventral view. C. Right lateral view of head. D. Dorsal view of head. E. Ventral view of left hand. F. Ventral view of left foot. Photos by N. A. Poyarkov. Coloration in preservative. After five years of storage in ethanol, the warm reddish, yellowish and orange tints have significantly faded, the specimen looks dark greyish-brown; however all Xenophrys major features of coloration pattern are still well-discernable. Variation. Raw and adjusted mensural data of the type series are presented in Tables 1 and 1s , respectively. Males have smaller body sizes than females, and their SVL values do not overlap (male SVL = 23.2-25.6 mm, average 24.4 +/- 0.8 mm; vs. female SVL = 26.2-29.2 mm, average 28.2 +/- 1.2 mm). The members of the type series generally agree in coloration with that of the holotype (see Fig. 5 ). Males ZMMU A-7607 (Fig. 5A ) and ZMMU A-7608 (Fig. 5C ) have generally lighter pinkish-grey coloration of ventral surfaces. The shape of ventral reticulum varies from having dense small yellowish and blackish spots (as in male AUP-00662, Fig. 5E ) to larger intermittent longitudinal black blotches with yellowish veins between them (as in males ZMMU A-7607 and ZMMU A-7608, Fig. 5A, C ). Males AUP-00661 and AUP-00662 originally had damaged and partially regenerated left hind limbs (Fig. 5D-E ). Other morphological features showed no significant variation among the type series. Figure 5. Male paratypes of Ansonia karen sp. nov. in dorsal (upper row) and ventral (lower row) views from Suan Phueng District, Ratchaburi Province, western Thailand. A. ZMMU A-7607. B. ZMMU A-7606. C. ZMMU A-7608. D. AUP-00661. E. AUP-00662. Photos by N. A. Poyarkov. Larval morphology. Description based on AUP-02091 at Gosner (1960) stage 38. Total length 16.9 mm, head-body length 6.2 mm, head-body depth 2.4 mm, maximum head-body width 3.3 mm, diameter of eyeball 0.9 mm, interorbital distance 1.4 mm, eye to tip of snout 1.7 mm, internarial distance 1.1 mm, width of oral disc 3.0 mm, tail length 10.8 mm, maximum tail depth 2.4 mm, tail muscular depth 1.7 mm, thigh length 1.0 mm, tibia length 1.2 mm, foot length 1.7 mm. Body distinctly flattened dorsoventrally (Fig. 6A ), broadly oval-shaped in dorsal and ventral views with maximum width posterior to eyes (Fig. 6B ); snout broadly rounded in dorsal view (Fig. 6B ); eyes with dorsolateral orientation; nostrils located closer to eyes than to tip of snout, with anterolateral orientation. Oral disc ventral, forming a sucker, comprising ca. 93% of head-body width, not emarginate, both oral labia expanded (Fig. 6D ); anterior labium slightly smaller than posterior labium, separated from tip of snout by deep groove; marginal papillae in single row across posterior labium and not discernable on anterior labium, submarginal papillae in two rows on posterior labium; black, serrated jaw sheaths, upper divided with gap of ca. same length as single sheath, lower continuous; labial tooth (keratodont) row formula 2/3, all rows continued, well separated from jaw sheaths, anterior rows medially curved, slightly longer than posterior rows (Fig. 6D ); tail musculature well-developed, tapering posteriorly to pointed tail tip; tail deepest in anterior one third of length; dorsal and ventral fins approximately equal in depth. Figure 6. The tadpole of Ansonia karen sp. nov. (AUP-02091) from Suan Phueng District, Ratchaburi Province, western Thailand in life. A. Lateral view. B. Dorsal view. C. Ventral view. D. Close-up of the oral disc. Photos by M. Naiduangchan. Tadpole coloration. In life (Fig. 6 ) dorsal surfaces of body and tail dark violet-brown with numerous, golden and bronze-colored specks scattered along tail, getting denser on body anteriorly and laterally and around eyes (Fig. 6B ). Laterally dark violet-gray with bright golden or metal specks on tail and body flanks; limbs dorsally with bronze specks and transverse dark bands (Fig. 6B ). Ventrally semi-translucent lavender-gray lacking golden specks (Fig. 6C ). After three years in preservative, dorsal surfaces of body turned grayish-brown, with densely well-discernable scattered brown chromatophores; ventral surfaces with very few chromatophores medially getting denser laterally; dorsal and ventral tail fins transparent with few chromotaphores. Distribution. Ansonia karen sp. nov. is currently known only from the type locality and nearby locality in same forest stream in the environs of Khao Laem Mountain, in Suan Phueng District of Ratchaburi Province in western Thailand, less than 2.0 km from the international Thai-Myanmar border (Fig. 1 ). The new species likely inhabits the middle portion of the Northern Tenasserim Mountain range (between the Kanchanaburi and Prachuap Khiri Khan provinces), and is expected to occur in adjacent montane areas in the western part of Phetchaburi Province of Thailand and Thanintharyi Division of Myanmar. Natural history. The new species inhabits a polydominant montane tropical evergreen forest on Khao Laem Mountain at elevations from ca. 700 to 750 m a.s.l., where the adult specimens were observed at night perched on leaves or stones (Fig. 7B-C ) along an approximately 1-3 m wide, slow-flowing mountain stream (Fig. 7A ), or beneath stones along the stream's edge. The multi-species polydominant tropical forest at the type locality has dense vegetation with tangles of giant bamboo Dendrocalamus asper (Schult.) Backer. Males were calling during our field observations from June to November throughout 2017-2019. The tadpoles of the new species were recorded in the same stream and were usually concentrated in pools under small waterfalls, hiding under gravel on the stream bottom, or sitting on the vertical surfaces of large submerged boulders to which they were attached by their oral discs (Fig. 7D ). Figure 7. Natural history of Ansonia karen sp. nov. A. Breeding habitat of the new species Ansonia karen sp. nov. in Suan Phueng District, Ratchaburi Province, western Thailand. B. Female of the new species in situ (not collected). C. Male of the new species in situ (not collected). D. Tadpole at Gosner (1960) stage 38 (AUP-02091, left), and a metamorph at Gosner (1960) stage 44 (AUP-02092, right) in situ . Photos by M. Naiduangchan. The species of amphibians and reptiles recorded in sympatry with the new species at the type locality include: Leptobrachium tenasserimense Pawangkhanant, Poyarkov, Duong, Naiduangchan & Suwannapoom, L. smithi Matsui, Xenophrys cf. major (Boulenger), Leptobrachella melanoleuca (Matsui), L. fuliginosa (Matsui), Amolops panhai Matsui & Nabhitabhata, Alcalus tasanae (Smith), Limnonectes jarujini Matsui, Panha, Khonsue & Kuraishi, L. doriae (Boulenger), L. macrognathus (Boulenger), M. berdmorei (Blyth), Acanthosaura crucigera Boulenger, Pseudoxenodon macrops (Blyth), Trimeresurus popeiorum Smith, and Rhabdophis chrysargos (Schlegel). Etymology. The specific name " Ansonia karen " is given as a noun in apposition and refers to the name of the Karen people. Originally inhabiting wide areas in southern and southeastern Myanmar, many Karen have migrated to Thailand, having settled mostly on the Thailand-Myanmar border, including the Suan Phueng District, the type locality of the new species, due to the political turmoil during the end of XX - beginning of XXI centuries. We received significant help and assistance from the local Karen community in Suan Phueng during our field surveys and want to thank them for their permanent support. NAP also thanks Karen Sarkisian for his support and encouragement. Comparisons. Ansonia karen sp. nov. is most closely related to A. thinthinae but differs from it by being smaller, more squat and having statistically significant differences in head and limb proportions (see above and Table 2 ). It differs in coloration and pattern from A. thinthinae in having (as opposed to lacking) red-tipped tubercles on the dorsum and flanks; lacking, as opposed to having, gular spotting; having irregularly shaped gray crossbars on the hind limbs as opposed to having regularly shaped, thin, yellowish crossbars; and the bottoms of the hands and feet being reddish-orange as opposed to black. Differences between, and among, other species in the Thai-Burmese clade are summarized in Table 5 . Table 5. Morphological and color pattern characters of the species of the Thai-Burmese clade of Ansonia . Bold character states are those that discretely separate A. karen sp. nov . from some or all the other species of the clade.

Species	Ansonia karen sp. nov	Ansonia inthanon	Ansonia khaochangensis	Ansonia kraensis	Ansonia kyaiktiyoensis	Ansonia pilokensis	phukentensis	Ansonia siamensis	Ansonia thinthinae
SVL (Female)	26.2-29.2	23.3-25.2	34-35.3	24.0-27.9	24	24.7-25.4	28.1-30.5	32.2-34.6	31.8
Maximum SVL (Male)	23.2-25.4	22.9-23.3	31.9-32	19.9-22.3	24	19.9-23.9	23.1-25.4	25.5-27.9	22.1-28.1
Snout projecting beyond lower jaw (1) or not (0)	1	1	1	1	1	1	1	1	1
Tympanum visible (1) or not (0)	1	1	1	1	1	1	1	0 or 1	1
Light coloured rictal tubercle(s) at the corner of the jaw present (1) or not (0)	1	1	1	1	1	1	1	1	1
Interorbital tubercle ridges present (1) or not (0)	0	0	0	0	0	0	0	0	0
Opening of vocal sac on right (1) or left (0)	1	1	1	0	/	0	1	0 or 1	0 or 1
Finger tips rounded or forming small discs (1) or expanded and spatulate (0)	1	1	1	1	1	1	1	1	1
Toe tips rounded or forming small discs (1) or expanded and spatulate (0)	1	1	1	1	1	1	1	1	1
1st finger reaching the disc of the 2nd (1) or not (0)	0	0	0	0	0	0	0	0	0
No. of fingers with nuptial pads	1	1	0	1	0	2	2	1	1 + 2
No. of free phalanges of V toe	0.5	0.5-1	2	0.5	1.5	0.5	0.5	1	0.5
No. of free phalanges of IV toe	2.5	2.75	3-3.5	0.5-2.0	3	2.75-3	3	2	2.75-3
No. of free phalanges of III toe	0.5	0.5-2.66	2	0.5-2.33	1.5-3	0.5-2	1	1	0.5-2
No. of free phalanges of II toe	0.5	0.5-2	1-1.5	0.5-2.0	0.5-1.5	0.5-1	0.5	1	0.5-1
No. of free phalanges of I toe	0.5	0.5-1	0.5	0.5-1.0	0.5	0.5	0.5	1	0.5
Tarsal ridge present (1) or not (0)	0	0	1	0	0	0	0	0	0
Inner metatarsal tubercle present (1) or not (0)	1	1	1	1	1	1	1	1	1
Outer metatarsal tubercle present (1) or not (0)	1	1	1	1	1	1	1	1	1
Submandibular tubercles in males present (1) or not (0)	1	1	0	1	1	1	1	0	1
Dorsal tubercles present (1) or not (0)	1	1	1	1	1	1	1	0	1
Dorsolateral row of enlarged tubercles present (1) or not (0)	1	0	0	0	0	1	0	0	1
Rows of tubercles on back (1) or not (0)	0	0	0	0	0	0	0	0	0
Oblique flap of skin on each side of vent (1) or not (0)	0	0	0	0	0	0	0	0	/
Abdomen coarsely granular (1), finely granular (2), or tuberculate (0)	1	1	1	1	1	1	2	2	1
Color or iris	Yellowish-gold	gold	black	Gold	Yellowish-gold	Gold	Gold	/	Yellow
Gular spotting present (1) or not (0)	0	1	0	0	0	1	0	1	1
Wide, light patch below eye (1) or not (0)	1	0	0	0-1	0	1	1	0	1
White postorbital patch present (1) or not (0)	0	0	0	0	0	0	0	0	0
Light spot between the scapulae present (1) or not (0)	1	1	0	1	1	1	1	0	1
Light crossbar on hind limbs present (1) or not (0)	1, irregular in shape	1	0	1	1	1 (faint)	1	1	1
Vertebral stripe present (1) or not (0)	0	0	0	0	0	1	0-1	0	0
Discrete white or bright yellow spots along the underside of lower jaw large (2), small (1) or absent (0)	2	2	0	1	2	2	2	2	2