Tylototriton zaimeng, Decemson & Lalremsanga & Elangbam & Vabeiryureilai & Shinde & Purkayastha & Arkhipov & Bragin & Poyarkov, 2023

Decemson, Ht., Lalremsanga, Hmar Tlawmte, Elangbam, Premjit Singh, Vabeiryureilai, Mathipi, Shinde, Parag, Purkayastha, Jayaditya, Arkhipov, Dmitriy V., Bragin, Andrey M. & Poyarkov, Nikolay A., 2023, A new cryptic species of Tylototriton (Amphibia, Caudata, Salamandridae) from mysterious mountain lakes in Manipur, north-eastern India, Herpetozoa 36, pp. 203-224 : 203

Tylototriton zaimeng sp. nov.

; Figs 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 Proposed English name: Zaimeng Lake Crocodile Newt

Type material.

Holotype. MZMU3041, an adult female from a swamp on forest clearing surrounded by montane evergreen tropical forest in Chingjaroi Ngachaphung, Ukhrul District, Manipur State, north-eastern India (coordinates 25.385°N, 94.458°E; elevation 1,630 m a.s.l.; datum = WGS84), collected on 20 November 2022 at 18:00 h by Ht. Decemson.

Paratypes. MZMU3035-3036, two adult males from a forest lake in Phungyar (environs of Tangkhul Hungdung), Kamjong District, Manipur State, north-eastern India (coordinates 24.811°N, 94.245°E; elevation 1,184 m a.s.l.), collected in July 2022 by Ht. Decemson and Shamungou; MZMU-2942-2947, six adult females from the Zaimeng Lake, Koubru Forest Division, environs of Chawangkining Village, Kangpokpi District, Manipur State, North-eastern India (coordinates 25.238°N, 93.944°E; elevation 2,212 m a.s.l.), collected on 18 July 2022 at 18:00 h by Ht. Decemson; MZMU-2948-2950, three adult males from the Zaimeng Lake, Koubru Forest Division, environs of Chawangkining Village, Kangpokpi District, Manipur State, north-eastern India (coordinates 25.238°N, 93.944°E; elevation 2,212 m a.s.l.; datum = WGS84), collected on 18 July 2022 at 18:00 h by Ht.Decemson.

Referred specimens.

MZMU-3037-3040, four larvae premetamorphic stage 45 ( Bernardes et al. 2017) from the same locality and with the same collection information as the holotype.

Diagnosis.

The new species is assigned to the genus Tylototriton by having the following combination of morphological attributes: (1) the presence of dorsal granules, (2) dorsolateral bony ridges on the head, (3) the presence of dorsolateral series of rib nodules (knob-like warts); and (4) the absence of a quadrate spine and molecular data (see Fig. 2 ). Tylototriton zaimeng sp. nov. is distinguished from all other congeners by a combination of the following morphological attributes: (1) medium body size, adult SVL 61.4-67.5 mm in males, 61.6-68.7 mm in females; (2) tail comparatively short, subequal or slightly longer than body in both sexes, lacking lateral grooves; (3) skin roughly granulated; (4) head massive and wide, relative maximal head width comprising 24.3-27.9% of SVL; (5) snout rounded in dorsal view; (6) supratemporal bony ridges on head very wide, protruding, with rough surface, beginning at the snout; (7) sagittal ridge on head well-distinct, very wide and protruding; (8) limbs comparatively short, tips of fore-limb and hind-limb not overlapping when adpressed along body; (9) vertebral ridge distinct, wide and not segmented; (10) rib nodules distinct, 13-14 along each side of body; (11) background colouration brown; (12) head, vertebral ridge, rib nodules, palms, soles, vent and ventral tail ridge with dull orange to yellowish-brown markings; (13) vomerine teeth organised in two distinctly curved bell-shaped widening anteriorly series, with 81-113 teeth.

Comparisons.

The new species can be easily distinguished from members of the subgenus Tylototriton Yaotriton (clades 3-5 in Fig. 2 ) by having light colour markings on head, vertebral ridge, rib nodules, palms, soles, vent and ventral tail ridge (vs. dark body colouration, except for palms and soles, vent region and ventral ridge of tail in most members of the subgenus Tylototriton Yaotriton with the exception of T. panhai ). The new species can be further distinguished from T. panhai by having light colour markings on entire limbs (vs. distinct light markings only on palms, soles and fingers in T. panhai ). Tylototriton zaimeng sp. nov. can be distinguished from T. taliangensis (member of clade 2, Fig. 2 ), by having light markings on distinct rib nodules, lips and parotoids (vs. lacking distinct rib nodules, generally dark charcoal-black body colouration with light orange to red markings only on the posterior part of parotoids, digits, palms, soles, vent and ventral tail ridge in T. taliangensis ). Tylototriton zaimeng sp. nov. can be distinguished from T. pseudoverrucosus (clade 2, Fig. 2 ) and T. kweichowensis (clade 1, Fig. 2 ) by having isolated light markings on rib nodules (vs. connected markings forming light dorsolateral lines in T. pseudoverrucosus and T. kweichowensis ).

Based the results of phylogenetic analyses (Fig. 2 ), Tylototriton zaimeng sp. nov. falls into clade 1 of the subgenus Tylototriton Tylototriton s. str. and, hence, morphological comparisons with members of the T. verrucosus species group members appear to be the most pertinent. Morphological comparisons on several diagnostic characters between Tylototriton zaimeng sp. nov. and the closely-related members of T. verrucosus species group are summarised in Table 4 . An important morphological difference which distinguishes Tylototriton zaimeng sp. nov. from all other members of T. verrucosus species group members is the shape of vomerine tooth series (VTS), which are distinctly curved and bell-shaped in the new species (Fig. 4A ): VTS are distinctly widening in the anterior one-third of their length, further gradually widening posteriorly, reaching maximal width in the posterior one third of VTS length; this shape of VTS appears to be quite stable and was observed in all examined adult specimens of the new species. In contrary, in all members of T. verrucosus species group for which the shape of VTS was reported (in T. houi , T. panwaensis , T. kachinorum , T. verrucosus , T. shanjing , T. uyenoi , T. anguliceps , T. podichthys and T. yangi ), it was described as inverted V-shape with VTS branches being comparatively straight in the anterior half of their length (see Fig. 4B ).

Tylototriton zaimeng sp. nov. can be further distinguished from T. uyenoi , T. pulcherrimus , T. shanjing , T. houi and T. yangi by having dull orange-brown to yellowish-brown light markings (vs. much brighter orange to bright-yellow light markings in T. uyenoi , T. pulcherrimus , T. shanjing and T. yangi and vs. bright orange-red markings in T. houi ). In particular, T. houi has bright orange-red markings on ventral surfaces including vent, chest, light mid-ventral line (vs. absent in the new species); T. pulcherrimus has a series of bright-orange glandular spots located ventro-laterally and on flanks (vs. flanks lacking light spots in the new species); while T. yangi has contrasting charcoal-black colouration of head and lips with only posteriormost part of parotoid colored bright orange and no light ventral markings on body and tail (vs. all head dull orange-brown, light markings present on ventral tail ridge and vent in the new species). Tylototriton zaimeng sp. nov. has relatively narrower head in both sexes (RHW 22.2 vs. 25.0 in males; 21.6 vs. 23.1-24.0 in females); shorter internarial distance (RIND 5.7 for males, 5.8 for females vs. 7.0-7.1 for both sexes); and very wide, protruding, and glandular dorsolateral and sagittal head ridges (vs. narrow steep ridges) than in T. uyenoi (see Table 4 ). Males of the new species can be further diagnosed from males of T. umphangensis by having shorter limbs which do not overlap when adpressed along the body (vs. overlap), by comparatively longer trunk (RTRL84.4 vs. 76.8), longer tail (RTAL 110.6 vs. 104.7), by having snout rounded in dorsal aspect (vs. truncate) and by having a non-segmented vertebral ridge (vs. distinctly segmented) (see Table 4 ). Males of the new species can be further diagnosed from males of T. shanjing by having comparatively shorter head (RHL 23.8 vs. 26.6), longer tail (RTAL 110.6 vs. 104.4), by shorter internarial distance (RIND 5.7 vs. 7.1) and by having a non-segmented vertebral ridge (vs. well-segmented) and brown to dark-brown background body colour (vs. blackish) (see Table 4 ). Tylototriton zaimeng sp. nov. can be distinguished from T. verrucosus by having light ventral markings on body and tail (vs. no light markings on body and tail). The new species can be further differentiated from T. verrucosus by having comparatively shorter internarial distance in both sexes (RIND 4.8-6.7 vs. 6.2-7.0) and longer tail in both sexes (RTAL 110.6 vs. 104.9 for males; 105.3 vs. 102.5 for females); the new species also has a non-segmented vertebral ridge (vs. well-segmented) and brown background colouration of body (vs. blackish) (see Table 4 ).

Tylototriton zaimeng sp. nov. can be distinguished from T. podichthys by having comparatively shorter head in both sexes (RHL 21.8-25.6 vs. 28.1-34.3), slightly longer tail in both sexes (RTAL in males 108.1-114.1 vs. 80.2-104.8; in females 96.6-112.2 vs. 79.2-81.4), in having 13-14 rib nodules (vs. 15-16 rib nodules), by comparatively shorter limbs which do not overlap when adpressed to body (vs. digit tips touching when limbs are adpressed to body) and by having duller colouration with orange to yellowish-brown light markings and brown background (vs. orange to dark-red light markings and blackish background) (see Table 4 ). The new species can be distinguished from T. phukhaensis by having very wide, protruding and glandular head ridges (vs. narrow steep head ridges), by having snout rounded in dorsal aspect (vs. truncate), by comparatively shorter limbs which do not overlap when adpressed to body (vs. digit tips touching when limbs are adpressed to body), by having comparatively wider head in both sexes (RHW 19.6-23.4 vs. 17.7-19.2), by having comparatively longer trunk in both species (RTRL 79.5-88.7 vs. 76.4-76.8) and by a having wide non-segmented vertebral ridge (vs. narrow, segmented) (see Table 4 ).

Tylototriton zaimeng sp. nov. can be distinguished from T. anguliceps by having a comparatively shorter head in males (RHL 22.5-25.6 vs. 26.2-29.5), by shorter internarial distance in both sexes (RIND 4.8-6.7 vs. 6.6-7.4), by having a wide non-segmented vertebral ridge (vs. weakly segmented), by having snout rounded in dorsal aspect (vs. truncate), by having very wide, protruding and glandular head ridges (vs. narrow steep head ridges, including narrow and long sagittal ridge), by having 13-14 rib nodules (vs. not less than 15 rib nodules), by comparatively shorter limbs which do not overlap when adpressed to body (vs. digit tips touching when limbs are adpressed to body) and by having duller colouration with orange to yellowish-brown light markings and brown background (vs. bright-orange markings and blackish background) (see Table 4 ).

The new species can be readily distinguished from T. shanorum by having smaller body size in both sexes (SVL 61.4-76.1 mm vs. 76.0-87.9 mm), by having comparatively narrower head in both sexes (RHW 19.6-23.4 vs. 24.8-26.3), by having comparatively longer trunk in both sexes (RTRL 79.5-88.7 vs. 74.3-77.6), by having snout rounded in dorsal aspect (vs. blunt to truncate), by comparatively shorter limbs which do not overlap when adpressed to body (vs. limbs overlapping when limbs are adpressed to body) and by having a wide non-segmented vertebral ridge (vs. weakly segmented) (see Table 4 ). Tylototriton zaimeng sp. nov. can be easily distinguished from T. ngarsuensis by having generally smaller body size in males (SVL 61.4-67.5 mm vs. 74.9-76.4 mm) and in females (SVL 61.6-76.1 mm vs. 102.3 mm), comparatively much narrower head in both sexes (RHW19.6-23.4 vs. 24.0-28.0), by notably more narrow internarial distance in both sexes (RIND 4.8-6.7 vs. 7.7-8.8), by having comparatively longer trunk in both sexes (RTRL 79.5-88.7 vs. 74.0-78.0), by having snout rounded in dorsal aspect (vs. truncate). The new species can be further distinguished from T. ngarsuensis by having dorsolateral head ridges starting at the snout (vs. posterior to orbit), by having a non-segmented vertebral ridge (vs. weakly segmented) and by having 13-14 rib nodules (vs. 15 rib nodules). Tylototriton zaimeng sp. nov. has much lighter and duller colouration than T. ngarsuensis : background colour brown (vs. nearly black) with light orange-brown markings on rib nodules and parotoids and limbs (vs. no light markings on rib nodules and parotoids) (see Table 4 ).

Tylototriton zaimeng sp. nov. can be easily distinguished from T. himalayanus from Nepal by the following morphological attributes: by notably narrower internarial distance in both sexes (RIND 4.8-6.7 vs. 8.2-8.4), by having generally longer trunk in both sexes (RTRL 79.5-88.7 vs. 77.1-79.9), by having longer tail in males (RTAL 108.1-114.1 vs. 98.0), by having snout rounded in dorsal aspect (vs. blunt), by comparatively shorter limbs which do not overlap when adpressed to body (vs. limbs overlapping when limbs are adpressed to body), by having 13-14 rib nodules (vs. 16 rib nodules) and by lacking lateral transverse grooves on tail (vs. clearly distinct) (see Table 4 ). The new species can be further distinguished from T. kachinorum from Kachin State of Myanmar by shorter head in both sexes (RHL 22.5-25.6 vs. 27.6 in males, 21.8-23.6 vs. 23.9-24.9 in females), by shorter tail in both males (RTAL 108.1-114.1 vs. 120.5), by notably narrower internarial distance in both sexes (RIND 4.8-6.7 vs. 7.7-8.0), by having snout rounded in dorsal aspect (vs. truncate) and by comparatively shorter limbs which do not overlap when adpressed to body (vs. limbs overlapping when limbs are adpressed to body) (see Table 4 ).

Phylogenetically and morphologically, Tylototriton zaimeng sp. nov. is most closely related to two species of Tylototriton inhabiting northern Myanmar and Yunnan Province of China - T. panwaensis and T. houi (see Fig. 2 , Table 4 ). From T. houi , the new species can be easily distinguished by its much duller colouration (see above and Table 4 ) and can be further distinguished by having snout rounded in dorsal aspect (vs. truncate), by having very wide, protruding and glandular head ridges with rough surface (vs. narrow steep head ridges with smooth surface, including short sagittal ridge) and by having 13-14 rib nodules (vs. 16 rib nodules).

From its sister species T. panwaensis , Tylototriton zaimeng sp. nov. can be distinguished by having snout rounded in dorsal aspect (vs. truncate), by having very wide, protruding and glandular head ridges including prominent sagittal ridge (vs. narrow steep head ridges with smooth surface, including very weak and low sagittal ridge), by having 13-14 rib nodules (vs. 15 rib nodules), by having a very wide non-segmented vertebral ridge (vs. narrow, weakly segmented), by lacking lateral transverse grooves on tail (vs. weak grooves present) and by comparatively shorter limbs which do not overlap when adpressed to body (vs. limbs overlapping when limbs are adpressed to body). Tylototriton zaimeng sp. nov. has generally lighter colouration than T. panwaensis : brownish-ground colour with orange-brown light markings (vs. more contrasting dark reddish-brown to black background colour with reddish-brown light markings in T. panwaensis ) (see Table 4 ). Moreover, males of the new species are different from males of T. panwaensis in a number of morphometric characters. Males of Tylototriton zaimeng sp. nov. have greater maximal head width (RMXHW 24.3-27.9 vs. 20.4-24.4), generally longer snout (RSL 9.2-11.2 vs. 8.7-9.6), wider interorbital distance (RIOD 12.3-14.3 vs. 9.9-10.7), smaller eyes (ROL 3.3-5.2 vs. 5.9-6.4) and wider tail base (RBTAW 10.4-15.2 vs. 7.9-9.5) than in T. panwaensis (see Table 3 ).

Description of holotype.

A medium-sized specimen in a good state of preservation (Figs 5 , 6 ). Head. Head slightly longer than wide (HW/HL ratio 92.8%) (Fig. 5C-E ), head slightly wider than body; pentagonal in shape in dorsal view, flattened in profile (Fig. 5E ); snout long, about three times longer than eye (UEW/SL ratio 36.6%), gently rounded in dorsal view (Fig. 5C ), rounded in lateral view (Fig. 5E ), notably projecting beyond lower jaw; nostrils on anterior margin of snout located notably closer to snout tip than to eye (NSD/ON ratio 39.9%), nostrils with antero-lateral orientation, not visible from dorsal view; eyes small, not projecting in lateral view (Fig. 5E ), slightly projecting in dorsal view (Fig. 5C ); labial folds absent; tongue oval, attached to anterior floor of mouth cavity, laterally and posteriorly free; vomerine teeth arranged in a bell-shaped distinctly curved series (Fig. 4A ), distinctly widening in the anterior one-third of vomerine tooth series length, further gradually widening posteriorly, reaching maximal width in the posterior one third of vomerine tooth series length; vomerine tooth series notably longer than wide (VTW/VTL ratio 40.4%), anteriorly reaching beyond the level of choanae, numbers of vomerine teeth 113 (62/51 in right and left branches, respectively), upper jaw teeth 72 and lower jaw teeth 90; parotoids distinct, large and protruding, bean-shaped, slightly projecting posteriorly (Fig. 5E ); dorsolateral supratemporal bony ridges on head very wide, with rough surface, notably protruding, continuing from the snout tip to the anterior end of parotoid, becoming wider towards the posterior end (Fig. 5C ); sagittal bony ridge on head very wide and protruding, becoming higher and wider posteriorly (Fig. 5C ); gular fold indistinct (Fig. 5D ). Body. Body habitus stout (Fig. 5A ); costal folds absent; vertebral mid-dorsal ridge very wide, not segmented, beginning at the occiput region and continuing to the anterior one fourth of tail length, separated from sagittal head ridge with gap subequal to eye in length (Fig. 5C ); rib nodules prominent, distinct, forming knob-like glandular warts, 14 on both sides of body, arranged in two longitudinal lines on dorsolateral surfaces of dorsum, running from area posterior to axilla to tail base (Fig. 5A ); on body, rib nodules almost of the same size, rounded, decreasing in size posteriorly on sacrum and tail basis. Limbs. Limbs comparatively short and slender (Fig. 5A ); fore-limbs slightly shorter than hind-limbs; relative length of fore-limb FLL/SVL ratio 35.1%, relative length of hind-limb ratio 37.6%; fore- and hind-limbs not overlapping when adpressed towards each other along sides of the body; fingers and toes well developed (Fig. 5F-I ), free of webbing; fingers four, comparative finger lengths: 1FL <4FL <2FL <3FL; toes five, comparative toe lengths: 1TL <2TL <5TL <4TL <3TL. Tail. Tail comparatively short and thick, slightly shorter than body length (TAL/SVL ratio 97.0%); tail laterally compressed on all of its length, gently tapering posteriorly, lateral grooves on tail absent; dorsal tail fin starting at the anterior one fourth of tail length, becoming more distinct posteriorly, with maximal tail height at posterior two thirds of tail length, dorsal and ventral tail fins smooth; tail tip pointed. Skin texture and skin glands. Skin dorsally very rough, with numerous small granules present on dorsal surfaces of head and dorsum (Fig. 5A, C ), lateral sides of body and tail; ventral surfaces more smooth with smaller granules arranged in transverse striations (Fig. 5B ); small granules regularly arranged on throat (Fig. 5D ); head ridges and parotoids with rough surface; skin on dorsal surfaces of limbs granular, on volar and plantar surfaces of hands (Fig. 5G ) and feet (Fig. 5I ) with tiny grooves forming a reticulated pattern; metacarpal or metatarsal tubercles absent. Cloacal region slightly swollen, vent as a longitudinal slit (Fig. 5J ), vent edges with small transverse folds.

Colour of holotype in life.

Ground colour of dorsal surfaces of head and trunk dark brown (Figs 5A , 6 ); dorsal surfaces of limbs and lateral surfaces of tail yellowish-brown to light orange (Fig. 5A ); iris dark-brown with copper speckles along its outer margins (Fig. 5E ); throat, belly and ventral surfaces of limbs light brown (Fig. 5B ); anterior parts of head, including snout, light orange to yellowish-brown; rib nodules and vertebral ridge light orange-brown, notably discernible from dark brown trunk colouration; upper and lower lips, head bony ridges and parotoids, palms and soles light-orange.

Colour of holotype in preservative.

After preservation in ethanol for six months, the colouration pattern of the holotype resembles that observed in life; however, yellowish and orange tints faded turning light brownish-grey.

Measurements and counts of the holotype.

Measurements of the holotype are presented in Table 3 . Additional morphometric characters (all in mm) include: ICD 9.1; CW 13.0; NSD 1.8; 1FL 3.8; 2FL 5.7; 3FL 6.7; 4FL 4.1; 1TL 3.1; 2TL 4.7; 3TL 8.6; 4TL 8.4; 5TL 4.8. Meristic characters: UJTN 72; LJTN 90; VTN 62/51 (right/left); DLWN: 14/14 (right/left). Body weight (when alive): 13.5 g.

Variation.

All individuals in the type series are generally similar in morphology and agree well with the description of holotype in body proportions and colouration; variation of morphometric characters within the type series is shown in Table 3 . Variation of the dorsal colouration in eleven paratypes in preservative is presented in Fig. 7 . The state of preservation of nine paratypes MZMU-2942-2950 is much worse than that of the holotype and the paratypes MZMU-3035-3036: they are desiccated what caused partial discolouration and skin damage (Fig. 7 ). Colouration of the paratypes MZMU-3035-3036 closely agrees with that described for the holotype. In general, males have more slender bodies than females. Males and females do not differ in body size (SVL 61.4-67.5 mm in males vs. SVL 61.6-68.7 mm in females) (Table 3 ).

Larval morphology.

Description of larval morphology is based on four premetamorphic larval specimens (MZMU-3037-3040, Bernardes et al. (2017) stage 45) (see Referred specimens for details).

Larval measurements

(n = 4; in mm). SVL 35.1 ± 2.5; HL 10.2 ± 0.7; HW 10.3 ± 0.7; OL 2.7 ± 0.2; AGD 21.1 ± 1.5; TAL 35.3 ± 2.5; FLL 11.9 ± 0.8; HLL 12.1 ± 0.8; MXTAH 5.2 ± 0.4.

Larval external morphology.

Body elongated, as high as wide (Fig. 8 ). Head large, ovoid in dorsal view, wide and slightly depressed with a short and rounded snout, gently sloping in lateral view, slightly wider than body in dorsal view. Snout rounded in dorsal view (Fig. 8B ), as well as in lateral view (Fig. 8A ). Tail equal to body length comprising 100.4% of SVL; myotomes on body and tail not discernible in lateral view. Nostrils rounded, small, orientated anterolaterally, located much closer to snout tip than to eye (Fig. 8A ). Eyes large, rounded, orientated dorsolaterally, well visible in dorsal view (Fig. 8B ). Limbs short, fore-limbs subequal to hind-limbs, FLL/HLL ratio 98.5%. Fore-limbs with four well-developed elongated fingers; relative finger lengths: 4FL <3FL <1FL <2FL. Hind-limbs with five well-developed toes; relative toe lengths: 5TL <1TL <2TL <4TL <3TL. Orbit diameter (OL) 7.7% of SVL. Vent a short longitudinal slit. Tail fins reduced; maximum height of dorsal tail fin ca. 10% of maximum tail height. Ventral tail fin almost completely reduced. Dorsal tail fin starts roughly above the cloaca, though it remains still visible as a thin mid-dorsal line starting at the level of axilla (Fig. 8B ). Tail tip pointed in lateral view (Fig. 8A ). Skin completely smooth; lateral line organs visible on dorsal surface of head; three pairs of gills partially reduced, not reaching the level of axilla.

Larval colouration in life.

In life, larval background colour ochre to light brown dorsally (Fig. 8A, B ), ventral surfaces of body off-white to pinkish, translucent, ventral surface of tail and vent bright yellow (Fig. 8C ). Dorsal surfaces of body, tail and head with indistinct dark-grey marbling. Eyes, except for pupil, fully pigmented, iris copper-coloured (Fig. 8A ).

Position in mtDNA genealogy and sequence divergence.

According to our mtDNA genealogy, Tylototriton zaimeng sp. nov. belongs to clade 1 of the subgenus Tylototriton Tylototriton s. str., corresponding to the T. verrucosus species group (see Fig. 2 ). The new species is grouped together with Tylototriton species from northern Myanmar ( T. panwaensis ), northern Indochina ( T. podichthys ) and Yunnan Province of China ( T. verrucosus , T. shanjing , T. houi and T. pulcherrimus ), forming clade with T. panwaensis and T. houi . Uncorrected genetic p -distances between Tylototriton zaimeng sp. nov. ND2 sequences and all homologous sequences of other members of T. verrucosus species group included in our analyses varied from 3.0% (with its sister species T. panwaensis ) to 8.6% (with T. uyenoi ) (see Table 2 ).

Distribution and Natural history.

To date Tylototriton zaimeng sp. nov. is known from five localities in montane areas of Manipur State, north-eastern India (see Fig. 1 : localities 2-6) on elevations from 1,180 to 2,210 m a.s.l. The actual extent of distribution of the new species remains unknown; it is likely that Tylototriton zaimeng sp. nov. occurs further northwards along the Khongtheng Mountain Range and other heavily forested highlands in the Nagaland State of India and even may penetrate to the easternmost parts of Arunachal Pradesh State of India and Sagaing Division of Myanmar. The taxonomic status of the existing record of Tylototriton sp. from Sagaing, Myanmar (Fig. 1 : locality 7), tentatively identified as T. cf. panwaensis by Grismer et al. (2019), requires further studies as it may represent a lineage closely related to Tylototriton zaimeng sp. nov.

Our knowledge on biology of Tylototriton zaimeng sp. nov. is incomplete. Adult animals were encountered both at night and during the day-time on the shallow parts of the lake (Fig. 9 ). The Zaimeng Lake, where the new species was for the first time encountered, is situated on top of Khongtheng Mountain Range at Thonglang Village (Bena Tababang); it is located on an elevation of ca. 2,212 metres above sea level and is one of the highest lakes in Manipur (Fig. 9A ). The lake total area measures about 90,580.46 m2 and is surrounded by evergreen montane forest composed of Michelia champacca , Phoebe hainensenia , Magnolia sp. and Quercus sp. with dense Arundinaria munro bamboo undergrowth ( Sebastian 2015; Singh et al. 2018). Adult male and female newts were observed slowly moving along the muddy bottom in clear water. Tylototriton zaimeng sp. nov. is locally abundant: in July, hundreds of adult newts could be seen on the bottom of Zaimeng Lake (Fig. 9B, C ). The new species is known to local Liangmei people as " Takope ", or " Tadui taku " in Liangmei dialect ( Singh et al. 2018), “Lengva” in Tangkhul and "Hangoi mamei panba" in Manipuri meaning "Tailed amphibian" ( Selim 2001). Other species of amphibians recorded syntopically with the new species at the type locality include Polypedates sp. and Zhangixalus sp.

Etymology.

The specific name " zaimeng " is given as a noun in apposition and represents a Latinised version of the Liangmei dialect word " Tylototriton zaimeng " literally meaning "Puzzle Lake" or "Mystery Lake". The name is given in reference to the Zaimeng Lake - a high-elevation mountain lake in Koubru Forest Division, the famous location where the crocodile newts were for the first time recorded in Manipur. It is believed that the name of the Lake was given by the Zeliangrong ancestors of Thonglang Village who passed by the Lake, but could not find their way to their destination as they used to return to the same spot again and again and circled the Lake over and over again ( Sebastian 2015).

Recommended vernacular names.

We recommend the following trivial name in English: Zaimeng Lake Crocodile Newt. The vernacular name in Liangmei dialect: Tadui taku ; Tangkhul: Lengva; Manipuri: Hangoi mamei panba.

Conservation status.

Tylototriton zaimeng sp. nov. is to date known from not more than five localities in montane areas of Manipur State of north-eastern India; the actual extent of range of the new species is unknown (see Fig. 1 ). The new species is anticipated to inhabit elevations above 1,000 m a.s.l. on mountains of the Khongtheng Mountain Range and could be possibly found in the adjacent parts of Nagaland and perhaps even the Sagaing Division of Myanmar. Further studies are needed to understand the current distribution range, population trends and possible threats to Tylototriton zaimeng sp. nov. The montane forests where the new species occurs are affected by growing forest destruction and anthropogenic pressure. Given this information, we tentatively suggest Tylototriton zaimeng sp. nov. to be considered as a Vulnerable (VU) species, following IUCN’s Red List categories (IUCN 2019).

Figures

Figure 1. Distribution of Tylototriton ssp. in India and adjacent areas and sampling localities examined in this study. Colours of icons correspond to species marked in Fig. 2; a dot in a centre of an icon indicates the type locality. For locality info, see Table 1. Tylototriton himalayanus: 1 - Mai Pokhari, Illam, Mechi, Nepal; T. zaimeng sp. nov.: 2 - Zaimeng Lake, Koubru Forest Division, Kangpokpi, Manipur, India; 3 - Zeliad, Manipur, India; 4 - Phungyar, Kamjong, Manipur, India; 5 - Shiroy Lily Hills, Manipur, India; 6 - Chingjaroi Ngachaphung, Ukhrul, Manipur, India; Tylototriton sp.: 7 - Lahe, Khandi, Sagaing, Myanmar; T. kachinorum: 8 - In Gyi Taung Mt., Indawgyi, Kachin, Myanmar; T. panwaensis: 9 - Sadung, Myitkyina, Kachin, Myanmar; 10 - Panwa, Myitkyina, Kachin, Myanmar; T. verrucosus: 11 - Sinlum, Momauk, Banmaw, Kachin, Myanmar; 12 - Nantin, Momien and Hotha valleys, Yunnan, China; T. houi: 13 - Yulong, Lijiang, Yunnan, China; T. ngarsuensis: 14 - Ngar Su, Taunggyi, Shan, Myanmar; T. shanorum: 15 - Pindaya, Heho and Aungpan, Kalaw, Shan, Myanmar; 16 - Taunggyi, Shan, Myanmar; 17 - Pinlaung, Shan, Myanmar.

Figure 2. Maximum Likelihood inference consensus tree of genus Tylototriton derived from analysis of 1,157 bp ND 2 and 508 bp 16 S rRNA gene fragments. For voucher specimen information, geographic localities and GenBank accession numbers, see Table 1. Distribution of the species of Tylototriton highlighted in colour is shown in Fig. 1. Numbers at tree nodes correspond to MLUFBS and BIPP support values, respectively. Photograph by Andrey M. Bragin.

Figure 3. Morphological comparison between Tylototriton zaimeng sp. nov. and T. panwaensis. A. Tylototriton panwaensis (adult male ZMMU NAP- 09477, from Sadung, Myitkyina, Kachin, Myanmar; photograph by Nikolay A. Poyarkov) and Tylototriton zaimeng sp. nov. (adult female MZMU 3041, from Chingjaroi Ngachaphung, Ukhrul, Manipur, India; photograph by Andrey M. Bragin) in life; B. PCA plots of PCA 1 versus PCA 2 for morphological parameters of the two Tylototriton species.

Figure 4. Vomerine tooth series of A. Tylototriton zaimeng sp. nov. (MZMU 3041) and B. T. panwaensis (ZMMU NAP- 09477). Drawing by Andrey M. Bragin.

Figure 5. Holotype of Tylototriton zaimeng sp. nov. (MZMU 3041, female) in life. A. Dorsal view; B. Ventral view; C. Head, dorsal view; D. Head, ventral view; E. Head, lateral view; F. Opisthenar view of right hand; G. Volar view of right hand; H. Opisthenar view of right foot; I. Plantar view of right foot; J. Ventral view of cloacal area. Photographs by Andrey M. Bragin.

Figure 6. Holotype of Tylototriton zaimeng sp. nov. (MZMU- 3041, female) in situ. Photograph by Andrey M. Bragin and Ht. Decemson.

Figure 7. Variation of dorsal colouration in paratypes of Tylototriton zaimeng sp. nov. Scale bar: 10 mm. Photographs by Andrey M. Bragin.

Figure 8. Lateral (A), dorsal (B) and ventral (C) views of larval specimen (MZMU 3037; Bernardes et al. (2017) stage 45) of Tylototriton zaimeng sp. nov. in life. Scale bar: 5 mm. Photographs by Andrey M. Bragin.

Figure 9. Natural habitat of Tylototriton zaimeng sp. nov. at Zaimeng Lake, Koubru Forest Division, Kangpokpi, Manipur, India. A. Vegetation surrounding the Zaimeng Lake; B. Males of Tylototriton zaimeng sp. nov. in situ; C. Breeding habitat of Tylototriton zaimeng sp. nov., numerous individuals can be seen on the muddy bottom of the lake. Photographs by Parag Shinde and Ht. Decemson.