SYS a008354 (Figs 3, 4A), adult male, collected by Jian Wang, Shuo Qi, and Hong-Hui Chen on 14 June 2020 from Mt Yunkai (22°16’32.90”N, 111°11’42.87”E; ca 1500 m a.s.l.), Xinyi, Guangdong, China.

Two adult males and one adult female (Figs 4B, C, D, 5A, B). Male SYS a008353 and female SYS a008355, the same collection data as the holotype; male SYS a004679 /CIB 116083, collected by Jian Wang, Zhi-Tong Lyu, and Zhao-Chi Zeng on 16 April 2016 from the same locality as the holotype.

The specific name sini refers to the outstanding biologist Prof. Shu-Szi Sin (= Shu-Zhi Xin, 辛树帜, 1894–1977). During his position at Sun Yat-sen University (1927–1931), Prof. Shu-Szi Sin organized repeated biology surveys throughout Guangxi, Guangdong, Guizhou, Hunan, and Hainan in southern China, pochally promoting the developments of zoological and botanic studies in this region. He collected specimens of T. asperrimus for the first time, as well as other amphibians and reptiles such as Quasipaa shini (Ahl, 1930) and the famous Shinisaurus crocodilurus Ahl, 1930. His family name “Sin” was mispronounced as “Shin” by the German researchers (Beolens et al. 2011), and we decided to use the correct spelling for this new species as Tylototriton sini sp. nov. in honor of Prof. Sin and his contributions.

Sin’s Knobby Newt (in English) / xīn shì yóu yuán (辛氏疣螈 in Chinese).

(1) Dorsolateral bony ridges on head low; (2) quadrate spines absent; (3) medium body size, TOL 118.4–124.5 mm in males, 144.5 mm in a single female; (3) snout obtusely rounded in dorsal view and rounded in lateral profile; (4) head longer than wide, HW/HL ratio 0.87–0.95; (5) supratemporal bony ridges and the sagittal ridge on head distinctly visible; (6) limbs slender, tips of forelimb and hindlimb overlapping when adpressed along the body; (7) vertebral ridge distinct, relatively smooth, not segmented; (8) rib nodules 12–13, relatively small, distinctly isolated from each other; (9) ground coloration dark brown; (10) digits orange with irregular dark brown mottling; (11) in breeding season, rib nodules mottled with orange coloration, much brighter in the first two rib nodules; (12) in breeding season, lateral tail dark brown, fin with dorsal orange margin, ventral tail ridge orange.

SYS a008354 (Figs 3, 4A), adult male with a stout body, medium in size (SVL 62.0 mm, TAL 56.4 mm). Head longer than wide (HW/HL ratio 0.93); maximum head width slightly larger than the maximum trunk width; head nearly rounded hexagonal in shape in dorsal view, depressed, gently sloping in profile. Snout obtusely rounded in dorsal view, rounded in profile view, projecting beyond lower jaw. Nostril on anterior margin of snout, located notably closer to snout tip than to eye, with anterolateral orientation, not visible from dorsal view. Tongue oval, not notched distally; vomerine tooth series in an inverted ‘V’ shape, converging anteriorly but not reaching choanae. Parotoids distinct, large, crescentshaped, slightly projecting posteriorly. Dorsolateral supratemporal bony ridges on head wide, distinctly protruding, beginning at the anterior corner of orbit continuing to anterior end of parotoid, posterior ends slightly curved inside; sagittal bony ridge on head strong.

Vertebral middorsal ridge distinct, wide, not segmented, running from occiput region to sacrum and the base of tail. Rib nodules distinct, relatively small, distinctly isolated from each other but arranged in two longitudinal series on dorsolateral surfaces of dorsum from shoulder to base of tail, counting 13 nodules on each side of body.

Limbs slender, forelimb and hindlimb overlapping when adpressed towards each other along body; fingers and toes well developed, lacking webbing or fringes; relative finger lengths I < IV < III = II, relative toe lengths I = V < II < III = IV. Tail long, TAL/SVL ratio 0.91; laterally compressed along entire length, tapering posteriorly, lateral grooves on tail distinctly visible in dorsal view.

Skin of dorsum, flanks, and lateral sides of tail very rough with small granules and larger warts. Skin of head ridges and middorsal vertebral ridge relatively smooth. Skin of limbs with numerous tiny tubercles. Ventral surfaces relatively smoother, corrugated, with smaller granules arranged in transverse striations; throat with numerous tiny flat tubercles; weak gular fold present. Cloacal region slightly swollen, vent as a longitudinal slit, vent edges with numerous small transverse folds.

In life (Fig. 3), ground color of head, dorsum, lateral tail, limbs, and venter uniform dark brown. Rib nodules mottled with orange coloration, the coloration of the first two rib nodules much brighter. Dorsal skin of hands and feet excluding the digits dark brown. Digits orange, with irregular dark brown mottling. Tail fin with dorsal orange margin, ventral tail ridge orange.

In preservative (Fig. 4A), ground color of head, dorsum, tail, limbs, and venter uniform dark. Orange coloration on all rib nodules fade. Orange coloration on the digits change into light brown. Ventral tail ridge pale yellow. Vent region pale yellow.

Measurements of the type series are given in Table 2. The single female paratype SYS a008355 (Figs 4D) possesses a larger and more robust body, however, its tail is relatively shorter, TAL/SVL ratio 0.82 vs 0.87–0.91 in males. Both the male holotype SYS a008354 (Figs 3, 4A) and the male paratype SYS a004679 (Figs 4B, 5A) bear 13 rib nodules on each side of body, while only 12 rib nodules in the male paratype SYS a008353 (Figs 4C, 5B) and the female paratype SYS a008355 (Figs 4D). In life, all rib nodules mottled with orange coloration, and much brighter in the first two rib nodules in several individuals (Figs 3, 5A, 5C).

Tylototriton sini sp. nov. was recorded as T. asperrimus for a long time, but can be distinguished by the head longer than wide (vs head wider than long in T. asperrimus), the snout obtusely rounded in dorsal view (vs truncate), the distal tip of limbs greatly overlapping when the fore and hind limbs pressed along the trunk (vs slightly overlapping or just meeting), rib nodules small and distinctly isolated from each other (vs rib nodules large, knob-like, and nearly in contact with each other), rib nodules with orange coloration (vs rib nodules completely black or brown), and tail fin with dorsal orange margin (vs completely brownish black).

Tylototriton sini sp. nov. further differs from other congeners within the clade IV (Fig. 2) by the head longer than wide (vs head wider than long in T. hainanensis, T. thaiorum Poyarkov, Nguyen & Arkhipov, 2021, and T. ziegleri), snout obtusely rounded in dorsal view (vs truncate in T. pasmansi, T. sparreboomi, T. notialis Stuart, Phimmachak, Sivongxay & Robichaud, 2010, and T. ziegleri), snout rounded in profile view (vs slightly angular in T. pasmansi and T. notialis), sagittal bony ridge on head strong (vs obscure in T. hainanensis), vertebral ridge not segmented (vs segmented, forming a row of tubercles in T. ziegleri), absence of orange markings on the parotoid (vs present in T. pasmansi and T. notialis), and the presence of orange coloration on all rib nodules (vs absent in T. hainanensis, T. pasmansi, T. sparreboomi, T. thaiorum, and T. ziegleri).

For the species within clades III and IV (Fig. 2), Tylototriton sini sp. nov. can be distinguished from T. panhai Nishikawa, Khonsue, Pomchote & Matsui, 2013 by the absence of orange markings on the parotoid (vs present); from T. vietnamensis Böhme, Schöttler, Nguyen & Köhler, 2005 by the presence of gular fold (vs absent); from T. maolanensis by the smaller body size with TOL 118.4–124.5 mm in adult males (vs larger body size with TOL 151.0–172.0 mm in adult males); and from T. anhuiensis Qian, Sun, Li, Guo, Pan, Kang, Wang, Jiang, Wu & Zhang, 2017, T. broadoridgus, T. dabienicus Chen, Wang & Tao, 2010, T. liuyangensis Yang, Jiang, Shen & Fei, 2014, T. lizhengchangi Hou, Zhang, Jiang, Li & Lu, 2012, and T. wenxianensis by the rib nodules swollen and distinctly isolated from each other (vs rib nodules not separated, almost in continuous longitudinal rows).

For the remaining species within clades I and II (Fig. 2), Tylototriton sini sp. nov. can be distinguished from T. taliangensis Liu, 1950 by the absence of orange markings on the parotoid (vs present); from T. pseudoverrucosus Hou, Gu, Zhang, Zeng & Lu, 2012, T. anguliceps Le, Nguyen, Nishikawa, Nguyen, Pham, Matsui, Bernardes & Nguyen, 2015, T. himalayanus Khatiwada, Wang, Ghimire, Vasudevan, Paudel & Jiang, 2015, T. kachinorum Zaw, Lay, Pawangkhanant, Gorin & Poyarkov, 2019, T. ngarsuensis Grismer, Wood, Quah, Thura, Espinoza, Grismer, Murdoch & Lin, 2018, T. panwaensis Grismer, Wood, Quah, Thura, Espinoza & Murdoch, 2019, T. phukhaensis Pomchote, Khonsue, Thammachoti, Hernandez, Peerachidacho, Suwannapoom, Onishi & Nishikawa, 2020, T. podichthys Phimmachak, Aowphol & Stuart, 2015, T. pulcherrima Hou, Zhang, Li & Lu, 2012, T. shangjing Nussbaum, Brodie & Yang, 1995, T. shanorum Nishikawa, Matsui & Rao, 2014, T. uyenoi Nishikawa, Khonsue, Pomchote & Matsui, 2013, and T. verrucosus Anderson, 1871 by its limbs dark brown except for the orange digits, palms, and soles (vs limbs uniformly orange or light brown); and from T. kweichowensis and T. yangi Hou, Zhang, Zhou, Li & Lu, 2012 by its tail dark brown, except fin with dorsal orange margin and ventral tail ridge orange (vs tail uniformly orange).

Tylototriton sini sp. nov. is currently known only from its type locality Mt Yunkai and the neighboring Mt Ehuangzhang (this study; Hernandez 2018), both situated in the Yunkai Mountains of western Guangdong.

This newt is terrestrial and inhabits leaf litters in well-preserved montane evergreen broad-leaf forest. During its breeding season from April to July, adult individuals can be observed in small ponds with muddy bottoms, small marshes, and vernal pools. Larvae can be found from June to August. On 15 August 2017, different stages of larvae were observed in the same vernal pool near the road (ca 2 m long and ca 3 m wide of the pool with water depth ca 4 cm), without adults observed (Fig. 6).

The extent of occurrence of Tylototriton sini sp. nov. is estimated to be less than 100 km², and the area of occupancy is estimated to be less than 10 km². Habitat degradation due to tourism development and illegal capture are the major threats. We recommend Tylototriton sini sp. nov. to be listed as Critically Endangered (CR) [IUCN Red List criteria B1ab(iii)+2ab(iii)]. This species must be added in the Appendix II of CITES, as the Tylototriton spp. are collectively included (CITES 2021). National Forestry and Grassland Administration of China (2021) has declared that the species T. asperrimus (as Y. asperrimus) is one of the Class II protected species of China, which was before the description of Tylototriton sini sp. nov. in this work. Therefore, the “T. asperrimus (as Y. asperrimus)” being listed as protected species of China should include the Guangdong population (now Tylototriton sini sp. nov.). Thus, we suggest Tylototriton sini sp. nov. should be also regarded as protected species of China with at least Class II.