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Neotype designation and redescription of Tropidophorus guangxiensis Wen, 1992 (Squamata: Sauria: Scincidae), with description of a new subspecies from central South China

The genus Tropidophorus consists of small semi-aquatic lizards that dwell in lowland forest steams (Barbour, 1921; Bauer & Jackman, 2008). Here, we designate the neotype and re-describe T. guangxiensis Wen, 1992 based on newly collected topotypic specimens. We also describe a new subspecies from Xuefeng Mountain, Hongjiang County, Hunan Province, central South China. Based on two mitochondrial genes (12S rRNA and 16S rRNA), the phylogenetic position of T. guangxiensis is allocated for the first time. Additionally, our data strongly support that the new subspecies is phylogenetically closely related to T. g. guangxiensis. We also present a morphological identification key for known species and subspecies of Tropidophorus in China.

The ML and BI phylogenies were congruent, with relatively high nodal support for most terminal nodes ( Figure 1B). The genus Tropidophorus was divided into two monophyletic groups (BPP/BSP=1.00/100). The four Chinese species (T. berdmorei, T. guangxiensis, T. hainanus, and T. sinicus) were assigned to the same clade, with T. guangxiensis most closely related to T. sinicus. The specimens from Hongjiang County formed a sister lineage to T. guangxiensis (BPP/BSP= 1.00/100). The interspecific genetic distances (based on 16S rRNA) for Tropidophorus ranged from 0.3% to 10.7%. The genetic distance between T. guangxiensis and the putative new subspecies T. guangxiensis was 2.7%, equivalent to that between T. latiscutatus and T. matsuii (2.1%) and between T. thai and T. robinsoni (2.4%).
The newly collected specimens of T. guangxiensis matched the diagnosis of the original description. In addition, based on our data, the Hongjiang population of Tropidophorus was most similar to T. guangxiensis, but showed a certain level of genetic and morphological differentiation from the topotypic population of T. guangxiensis (see below). Due to the limited comparative materials of true T. guangxiensis, we tentatively consider the Hongjiang population as a new subspecies of T. guangxiensis. Wen, 1992 (Supplementary Figures S1-S3; Supplementary Tables S3-S6) Chresonymy: Tropidophorus guangxiensis: Wen YT, 1992, Asiatic Herpetological Research, Berkeley, 4: 18-22. Type locality: Damingshan, Wuming Xian (county), Guangxi Zhuang Autonomous Region, China, 1 240 m a.s.l. Justification of neotype designation: Wen (1992) described T. guangxiensis based on three specimens (one juvenile and two adult males), which were deposited at the Department of Biology, Guangxi Medical College (GMC). According to information provided by Mr. Qi-Ping Hu (Director of the Department of Cell Biology and Genetics, former Department of Biology, Guangxi Medical University, Personal Communication, 2021), all three type specimens are presumed lost. Furthermore, as our new data suggest there may be additional cryptic diversity within T. guangxiensis, designating a neotype and re-describing the species definition have become essential. The neotype and paraneotype were from the same locality as the original type series, and they match the diagnosis of the species based on the type series by Wen (1992), including GMC 85-029, GMC 85-030, and GMC 85-032. Based on available morphological data, we believe the neotype and paraneotype represent the same taxa as the original type series, i.e., T. guangxiensis. Herein, we redescribe the species T. g. guangxiensis based on fresh specimens from the type locality and designate a neotype for this species. Diagnosis was updated based on the fresh specimens from the type locality and the original description. Neotype: HNU GKJ-2019007 (adult female), collected on 21 August 2019 by , Wuming County, Guangxi Zhuang Autonomous Region, China, at an altitude of 1 244 m a.s.l. Paraneotype: HNU GKJ-2019009 (sub-adult male), collected on 22 August 2019 by Ke-Ji Guo, Qi-Lin Pan, and Jian-Chun Li in Daming Mountain National Nature Reserve (N23°48'3'' and E108°45'32''), Wuming County, Guangxi Zhuang Autonomous Region, China, at an altitude of 1 280 m a.s.l. Diagnosis: Upper head scales strongly striated; supranasal absent; frontonasals 2, joined, longer than wide; prefrontals 2, joined or separated by small scale; interparietal single and small, without small transparent spot; parietals separated by interparietal, posterolateral border surrounded by 5-6 scales on each side; nuchal scales absent; supraciliaries 8, supraciliary row complete along length of lateral edge of supraoculars; loreals 2; presuboculars 1, upper anterior and lower posterior margin slightly convex, and terminal pointed; supralabials 8; infralabials 6-7; shallow groove on loreal-labial border, from posterior corner of nasal across subocular obliquely downward to end of sixth supralabial; midbody scales in 28-29 rows; paravertebral scales 45-50, not widened; ventral scales 50-53; midbody ventral scales 27-29; ventral scales of neck keeled; scale rows at tenth subcaudal 11-13; lamellae under fourth toe 17-18; scales of limbs keeled above and below; supralabials and infralabials black, each scale with white spot center; chin and throat grayish white with black marble; ventral of neck gray, each scale white in middle forming longitudinal white stripes; venter yellowish white; underside of tail white, subcaudals darkened on both sides, forming longitudinal white stripes. Description of neotype (detailed morphometric measurements in Supplementary Tables S3, S4): Body size relatively small (SVL of 62.5 mm; TaL of 68.8 mm).

Tropidophorus guangxiensis guangxiensis
Snout acute, rounded anteriorly; projecting beyond lower jaws; nostril laterally oriented, oval, closer to snout-tip than to orbit; head distinct from neck and body, longer than wide; head shape slightly flattened; upper head scales strongly striated; rostral wider than high, visible from above; supranasal absent; frontonasals 2, joined, longer than wide; prefrontals 2, separated by small scale; frontal narrowing posteriorly, in contact with frontonasal, prefrontals, first and second supraoculars, and frontoparietals; frontoparietals joined, bordered by frontal, second, third, and fourth supraoculars, parietals, and interparietal; interparietal single, without small transparent spot; parietals separated by interparietal, posterolateral border surrounded by five scales on each side; nuchal scales absent; nasal single, nostrils in posterior center, located closer to anterior loreal; loreals 2, weakly straited; posterior loreal higher and broader than anterior loreal; anterior loreal undivided, posterior loreal in contact with anterior loreal, prefrontal, first supraciliary, preocular, upper presubocular, second and third supralabial; preoculars 1; presuboculars 1, upper anterior and lower posterior margin slightly convex, and terminal pointed, in contact with third and fourth supralabials; supraciliaries 8, first two obviously larger, supraciliary row complete along length of lateral edge of supraoculars; supraoculars 4, second widest; postocular single; temporals strongly keeled; primary temporals 3; secondary temporals 4; eyes relatively small; pupil circle, discernable in preserved specimen; upper palpebrals 15; lower palpebrals 15-16; lower eyelid moveable, with six enlarged opaque scales, separated from supralabials by two rows of small scales; supralabials 8, fifth largest and sixth highest; upper parts slightly straited and lower parts smooth, except for first smooth overall; infralabials 7/6, first longest; shallow groove on loreal-labial border, from posterior corner of nasal across subocular obliquely downward to end of sixth supralabial; external ear opening ovoid, without lobules; tympanum superficial, tympanum diameter much smaller than eye length; mental wider than long, rounded anteriorly, in contact with first infralabial on each side and postmental; postmental undivided, in contact with mental, first infralabial on both sides and anterior pair of chinshields; chinshields in three pairs, first pair in contact anteriorly, second and third pairs separated by gular scale; first and second pairs of chinshields in contact with infralabials, third pair in contact anteriorly with infralabials and separated posteriorly from infralabials by small scales; tongue short; undivided anteriorly, tip obtuse, not pointed; teeth relatively small and somewhat pointed.
Body slender, midbody scales in 29 rows; dorsal scales in eight rows across back, slightly larger than lateral scales, imbricated; sharply keeled with acute-to-normal points, except several rows following interparietal smooth or keeled with at least two lines: paravertebral scales 50, not widened; lateral scales slightly smaller than dorsal and ventral scales, keeled with single line, obliquely upward or near horizontal; ventral scales smooth, except for ventral scales of neck keeled; ventral scales slightly larger than dorsal and lateral scales, in 50 transversal rows; midbody ventral scales in 29 transversal rows, counted from posterior margin of fore limb to last scale before precloacals; precloacals 4, inner precloacals overlapping outer ones, central two enlarged.
Limbs slender and short. Forelimbs shorter than hindlimbs; fingers 5, fourth finger includes claw beyond seventh supralabial and wrist reaches posterior margin of tympanum when adpressed forelimbs are carried forward; relative length of fingers I<V<II<III<IV, third and fourth fingers almost equal; each sharp, curved finger claw wrapped by two scales; subdigits smooth, 11 on fourth finger; all scales keeled; scales on dorsal surface of basal digit IV in two rows and terminal four scales in single row. Hindlimbs shorter than body length; toes 5, with sharp, curved claws enwrapped by two scales; fingers touching toes when limbs oppositely adpressed; fourth toe includes claw reaching wrist of forelimbs when limbs oppositely adpressed; relative length of toes I<II<III<V<IV; subdigits smooth, 17 on fourth toe; scales keeled above, smooth on ventral front.
Tail laterally compressed, relatively long, longer than SVL; tail tip acute; tail base wider than rest of tail; tail gradually tapering to point; dorsal scales of tail keeled, forming continuous ridge, scale rows 13, at tenth subcaudal; subcaudals 59; medial subcaudals divided from first to fifth, remaining ones approximately 1.5 times wider than neighboring scales; visceral fat bodies absent in abdomen. Figures S1-S3): Pupil black, iris brownish red. Head rusty brown dorsally and laterally, with yellowish, blackish cloudy spots; dorsum brown with irregular brownish red transverse bands and spots from neck to middle of body, body sides dark gray with irregular light brownish yellow dots from behind tympanum to groin; dorsally dark gray with brownish red dots; supralabials and infralabials black, each scale with white center spot; chin and throat grayish white with black marble; ventral neck gray, each scale white in middle, forming longitudinal white stripes; ventral body orange; ventral tail white, subcaudals darkened on both sides, forming longitudinal white stripes; limbs orange ventrally.  Figure S4). These skinks are known to be active in late August, but their diet and reproductive biology remain unknown. This subspecies is sympatric with Gonyosoma frenatum (Gray, 1853), Pareas boulengeri (Angel, 1920), and Takydromus sp. Comparisons: Based on the designated neotype and paraneotype, we compared Tropidophorus guangxiensis guangxiensis with congeners from China (morphological data of congeners were taken from literature: Fei et al., 2010;Guo et al., 2010;Rao et al., 2011;Wen, 1992;Yang & Inger, 1986;Yang & Rao, 2008;Zhang et al., 2012;Zhao & Adler, 1993;Zhao et al., 1999)  Snout acute (IN:IO ratio 0.38), rounded anteriorly; projecting beyond lower jaws; nostril laterally oriented; oval, situated closer to snout-tip than to orbit; nostril-snout distance 1.2 mm, eye-nostril distance 2.4 mm, eye-snout distance 3.8 mm (N-S:E-S ratio, 0.32; E-N:E-S ratio, 0.64); head distinct from neck and body, longer than wide; HL 9.8 mm, HW 7.8 mm (HL:HW ratio 1.25); head shape slightly flattened, HD 5.8 mm (HL:HD ratio 1.68), HNL 20.3. Upper head scales strongly striated; rostral wider than high, visible from above; supranasal absent; frontonasals 2, joined (suture length 1.2 mm), longer than wide, in contact with rostral, nasal, anterior loreal, and prefrontal on each side; prefrontals 2, separated by single small scale, in contact with frontonasal, anterior and posterior loreal, first supraciliary, first supraocular and frontal; frontal narrowing posteriorly, 1.51 times longer than distance to snout, and 1.61 times longer than interparietal length (2.0 mm), in contact with frontonasal, prefrontals, first and second supraoculars, and frontoparietals; frontoparietals joined (suture length 0.95 mm), bordered by frontal, third and fourth supraoculars, parietals and interparietal; interparietal single, small, without small transparent spot; parietals separated by interparietal and two small scales, posterolateral border surrounded by six scales on each side; without nuchal scales; nasal single, nostrils in posterior center, located closer to anterior loreal; loreals 2, straited; posterior loreal higher and broader than anterior one; anterior loreal undivided, posterior loreal in contact with anterior loreal, prefrontal, first supraciliary, preocular, upper presubocular, second and third supralabials; preocular 1; presubocular 1, upper anterior and lower posterior margin slightly concave, terminal blunt and rounded, in contact with third and fourth supralabials; supraciliaries 7, first two obviously larger, supraciliary row complete along length of lateral edge of supraoculars; supraoculars 4, second widest, followed by two small postsupraoculars; postocular single; pretemporals 2; postsuboculars 2, lower one in contact with sixth and seventh supralabials; temporals strongly keeled; primary temporals 3, lower one in contact with seventh supralabial; secondary temporals 5, upper one very large, in contact with parietal; eyes relatively small; pupil circle, discernable in preserved specimen; upper palpebrals 14; lower palpebrals 15; lower eyelid moveable, with six enlarged opaque scales, separated from supralabials by two rows of small scales; supralabials 8, fifth largest and sixth highest, upper part of supralabials slightly straited and lower part smooth from second to eighth supralabial; infralabials 7, first longest; shallow groove on loreal-labial border, from posterior corner of nasal across subocular obliquely downward to end of sixth supralabial; external ear opening ovoid, without lobules; tympanum superficial, tympanum diameter much smaller than eye length; mental wider than long, rounded anteriorly, in contact with first infralabial on each side and postmental; postmental undivided, in contact with mental, first infralabial on both sides, and anterior pair of chinshields; chinshields in three pairs, first pair in contact anteriorly, second pair separated by gular scale, third pair separated by three scales; first and second pairs of chinshields in contact with infralabials, third pair in contact with infralabials anteriorly and separated from infralabials by small scales posteriorly; tongue short; undivided anteriorly, tip obtuse, not pointed; teeth relatively small and somewhat pointed.

Coloration in life (Supplementary
Body slender, depressed, BW 12.5 mm (BW:SVL ratio 0.19); midbody scales in 33 rows; dorsal scales in eight rows across back, slightly larger than lateral scales, imbricated; scales of first four rows following interparietal striated, sharply keeled with acute to normal points posteriorly by fifth row; paravertebral scales 47, not widened; lateral scales slightly smaller than dorsal and ventral scales, keeled with single line, obliquely upward except for lower two rows near horizontal; ventral scales smooth, except for ventral scales of neck keeled; ventral scales slightly larger than dorsal and lateral scales, in 50 transversal rows, midbody ventral scales 31 transversal rows, counted from posterior margin of fore limb to last scale before precloacals; precloacals 4, inner precloacals overlapping outer ones, central two enlarged, left one overlapped by right one.
Limbs slender, short. Forelimbs 24.55% of SVL, shorter than hindlimbs (FLL 67.12% of HLL); with five fingers, fourth finger includes claw beyond sixth supralabial and wrist reaching middle of tympanum when adpressed forelimbs are carried forward; relative length of fingers I<V<II<III<IV, third and fourth fingers almost equal; each sharp, curved finger claw wrapped by two scales; subdigits smooth, counting as 4/5 on first finger, 9/8 on second finger, 12/11 on third finger, 12/12 on fourth finger, 7/7 on fifth finger; all scales keeled; scales on dorsal surface of basal digit IV in two rows and terminal four scales in single row. Hindlimbs shorter than body length (HLL 41.55% of SVL); toes five, with sharp, curved claws enwrapped by two scales; fourth toe includes claw reaching base of fourth finger when limbs are oppositely adpressed; relative length of toes I<II<III<V< IV; subdigits smooth, counting as 5/5 on first toe, 10/10 on second toe, 12/13 on third toe, 19/18 on fourth toe, and 11/10 on fifth toe; scales keeled above and smooth on ventral front.
Tail laterally compressed; base enlarged, gradually narrowing to acute point from end to tip; longer than tip of snout to vent length, latter almost 1.18 (SVL 84.65% of TAL); subcaudals enlarged, smooth, larger than dorsal scales, latter strongly keeled, form six continuous ridges on dorsal view; subcaudals 59, 14 scale rows at tenth subcaudal; medial subcaudals divided from first to sixth, remaining ones about two times wider than neighboring scales; visceral fat bodies absent in abdomen. Coloration in life ( Figure 1D, F): Pupil black, iris brownish red. Dorsal head, back, and tail base dark brown with indistinct light brownish red transverse bands, faded from anterior to posterior: one between anterior corners of eye, two on neck, six between limb insertions, five on tail base; dorsum with two rows of brownish red dots from neck to point above vent; body sides dark gray with irregular brownish red dots from behind tympanum to groin; supralabials and infralabials black, each scale with white center spot; limbs dorsally dark gray with brownish red dots; chin and throat black with brownish red spots; ventral of neck dark brown, each scale white in middle, forming longitudinal white stripes; ventral from posterior margin of fore limb to underside of tail base orange; underside of tail tip black; color of tail underside darkened from base to tip; brownish red ventrally with indistinct irregular dark transverse stripes.  Figure 1E; Supplementary Figures S2, S3K). Comments: The previous records of T. guangxiensis Mi et al., 2012) from the Xuefeng Mountain National Forest Park in Hongjiang County, Hunan Province, i.e., type locality of Tropidophorus guangxiensis hongjiangensis spp. nov., are therefore allocated to Tropidophorus guangxiensis hongjiangensis spp. nov.
It should be noted that there is a relatively high level of genetic divergence between T. g. guangxiensis and Tropidophorus guangxiensis hongjiangensis spp. nov., which is larger than the current interspecific genetic distances among recognized congeners (Supplementary Table S2). Future studies should collect additional specimens to gain a better understanding of the morphological and genetic variations with the genus Tropidophorus.
Water skinks in the genus Tropidophorus are a group of small, secretive, and elusive forest-floor dwelling lizards, and little is known about their diversity and distribution. The discovery of the new subspecies suggests an underestimation of the diversity of this group and a wider distribution of the genus than previously thought. In the past, distribution of the genus Tropidophorus was thought to be from the southern subtropical region of China, with the northern boundary of its distribution located in the Nanling Mountains at a latitude of N24° (Zhao et al., 1999). However, our recent discoveries push this limit further north to approximately N26° in Guizhou Province (Yang & Rao, 2008;Zhang et al., 2012). Our discovery of a new subspecies further extends the northern distribution of the genus to N27° latitude.

NOMENCLATURAL ACTS REGISTRATION
The electronic version of this article in portable document format represents a published work according to the International Commission on Zoological Nomenclature (ICZN); hence, the new names contained in the electronic version are effectively published under that Code from the electronic edition alone (see Articles 8.5-8.6 of the Code). This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank Life Science Identifiers (LSIDs) can be resolved and the associated information can be viewed through any standard web browser by appending the LSID to the prefixhttp://zoobank.org/.Publication LSID: urn:lsid:zoobank.org:pub:6C1DA4C8-9002-4D2F-B638-0EC701 AF3A5A Tropidophorus guangxiensis hongjiangensis LSID: urn:lsid: zoobank.org:act:A1382C7B-749B-4E6D-9B92-1B2653 CD0A28

SCIENTIFIC FIELD SURVEY PERMISSION INFORMATION
Permission for field surveys was granted by the Administration Bureau of the Xuefeng Mountain National Forest Park and the Administration Bureau of the Daming Mountain National Nature Reserve of Guangxi.

SUPPLEMENTARY DATA
Supplementary data to this article can be found online.