The following description is based on five tadpoles at Stages 26–27 (N = 2) and 36–37 (N = 3). Body ratio ranges represent all specimens. Raw measurements are given in Table 1.

CSUFT T10115 (Stage 37, Field voucher: MT05; GenBank accession number: ON209276), CSUFT T10117 (Stage 37; Field voucher: MT07; GenBank accession number: ON209284), and CSUFT T10119 (Stage 36; Field voucher: MT09; not sequenced), collected on 30 May 2021 from Tiantaishan (24.972277°N, 112.963394°E, ca. 1280 m a.s.l.), Mangshan, Hunan Province, China; and CSUFT T10944 (Stage 27, Field voucher: MT1104; not sequenced), and CSUFT T10945 (Stage 26; Field voucher: MT1105; not sequenced), collected on 16 November 2021 from the same site as the first specimens.

The body is oval, robust, and flattened above (BW/BL 53.3–55.7% at Stages 26–27, N = 2; and 53.6–55.2% at Stages 36–37, N = 3); the head is wider than the trunk; the eyes are located dorsolaterally, the pupils are round; the nares are oval, opening laterally, closer to the eye than to the tip of the snout (NE/SN 68.8–73.3% at Stages 26–27, N = 2; and 73.7–83.3% at Stages 36–37, N = 3); the internarial distance is smaller than the interorbital distance (IND/IOD 65.8–68.4% at Stages 26–27, N = 2; and 59.6–63.8% at Stages 36–37, N = 3); the rims of nares are raised from the body wall and directed posterolaterally; the spiracle is sinistral and low on the left flank; the spiracle tube is short, protruding posterodorsally, free from the body at the tip, and opening posterolaterally (SS/BL 55.6–62.0% at Stages 26–27, N = 2; and 57.3–58.1% at Stages 36–37, N = 3); the anal tube opens medially, unattached to the ventral fin; the dorsal fin arises behind the body-tail junction while the ventral fin is connected to the trunk; the tail muscle is massive, taller than tail fins before reaching the maximum tail height (TMH/MTH 55.6–55.8% at Stages 26–27, N = 2; and 48.4–50.8% at Stages 36–37, N = 3), and the tail tip is bluntly pointed, the tail length accounts for 71.7% (at Stages 26–27, N = 2) and 70.5–70.5% (at Stages 36–37, N = 3) of the total length; the mouth is terminal and the oral disc is funnel-like (BW/ODW 74.6–88.9% at Stages 26–27, N = 2; and 75.6–78.4% at Stages 36–37, N = 3); three and four rows of short oval submarginal papillae can be observed on the upper lip and lower lip, respectively; keratodonts are absent; the upper jaw sheath is brush-like, exhibiting a small median notch, while the lower jaw sheath is thin, sickle-shaped, weakly keratinized, and finely serrated.

In life, the background color of the head and trunk is dark brown; the dorsal pattern is pale brown interspersed with dark brown chromocytes, extending to above the horizontal level of the spiracle on the trunk from a lateral perspective; the dorsal surface of the anterior part of the tail is pale brown marbled with dark brown speckles; neuromasts are distinctly visible on the head, trunk and tail; the region between the anterior edges of the eyes and the median point of the upper lip is pigmented with a dark brown V-shaped pattern; the narial rims are pale brown; the oral disc is golden-pigmented, with a translucent edge; the submarginal papillae on lips are dark brown-pigmented. Laterally, the tail is pale brown-pigmented; dense goldish spots are located at the anterior part of the lateral surface of tail muscle, becoming smaller and at the middle, then disappearing posteriorly; three distinct dark brown stripes extended from the body-tail junction, and horizontally positioned at the anterior part of the tail; the upper and lower stripes end before reaching the maximum tail height, while the middle stripe is about half the length of the others; the upper and middle stripes are incomplete; the anterior part of the upper fin is opaque, marbled with goldish pigmentation and brown speckles; the anterior part of the ventral fin, as well as the anal tube are semi-translucent with dense large golden spots; the rest of the fins are semi-translucent, and exhibit sparse dark brown speckles interspersed with small goldish dots. The ventral surface of the body is rather dark; the belly is dark purplish covered with dense white spots; two longitudinal stripes, positioned ventrolaterally, extending from the snout to the vertical edge of the eyes posteriorly, and sometimes appear to broken; a transverse bar is positioned at the head-trunk junction of the vertical edge of the anterior spiracle and is always interrupted at the middle; the spiracle region and the corresponding region on the other side of the body, are covered with a short white stripe, that starts from the head-body connection, and terminated before reaching the region of the spiracle tube opening; regions without white pigmentation have less melanocytes; the gills and gut coils are indistinctly visible through the ventral skin. The eye sclera is silver with black dots; the iris periphery is wide and black; the iris is golden sprinkled with black dots; and the spiracle is translucent without pigmentation. In tadpoles at Stages 36–37, the hindlimbs are semi-transparent, and the outer aspect of the legs exhibits brown pigmentation interspersed with goldish chromocytes.

In preserved specimens, the tail stripes are still prominent; an incomplete V-shaped pigmentation pattern is still visible; the ventral pattern is translucent milky white; the golden pigmentation wanes on the oral disc; and the hindlimb bones are visible in ventral view in Stage 36–37 tadpoles.

Figure 1. 

Brachytarsophrys popei tadpoles in life A–C tadpole CSUFT T10117 (Stage 37) lateral view, dorsal view, and ventral view D ventral pattern of tadpole CSUFT T10119 (Stage 36) E ventral pattern of tadpole CSUFT T10945 (Stage 26); and F oral disc of tadpole CSUFT T10117 (Stage 37). D and E share the same scale bar with A–C.

Tadpoles of Br. popei differ significantly from the three syntopic Boulenophrys tadpoles described below by the unique pattern of two longitudinal white ventrolateal stripes on head, a transverse white bar on chest, and distinct large spots on belly (vs. absence of stripes and bars, and smaller spots/speckles on belly).

The differences in ventral pattern between four Brachytarsophrys tadpoles were compared by Li et al. (2020) and summarized in Table 2. The tadpole of Br. popei (Stage 29, N = 1) illustrated in their paper (also in Zhao et al. 2014, but marked as Stage 27), which was collected ~ 200 km north of Mangshan has a complete transverse white ventral bar. In contrast, our tadpoles (Stages 26–27, N = 2; and Stages 36–37, N = 3) consistently exhibit an interrupted white transverse ventral bar. This difference may be due to geographic variation or insufficient sample size. However, the presence of a transverse bar on chest could distinguish Br. popei tadpoles from Br. orientalis and Br. intermedia (vs. absent in both). In addition, the width of the transverse bar is markedly smaller than that in Br. chuannanensis (see Li et al. 2020: fig. 5E, F). Furthermore, compared with Br. intermedia, the tadpoles of Br. popei have a distinctly smaller size at Stage 36 (TTL 36.9 mm vs. 48.7 mm). Zhao et al. (2014) illustrated a metamorph of Br. feae at Stage 44 with several short stripes on belly (vs. spots or speckles in Br. popei, Br. orientalis, and Br. chuannanensis). We believe this pattern should be confirmed using more specimens at an earlier developmental stage in case this is a transitional form during metamorphosis. Further comparisons between Br. popei tadpoles and all megophryinid tadpoles that were identified using molecular data are shown in Tables 2 and 3.

All tadpoles were collected from an artificial roadside drainage ditch (Fig. 5C) at night while feeding beneath the water surface. Upstream of the ditch is a narrow, slow-moving stream with many rocks covered by moss. The ditch was rocky with a sandy substrate. The maximum depth of this ditch was ~ 0.5 m. Branches of plants from the mountain side of the road extended over this ditch, however, sunlight did reach the water surface at certain times of the day. Tadpoles were observed in a still water stretch behind big rocks, or a small dam formed by submerged leaf litter. Three tadpoles at Stages 36–37 were collected on 30 May 2021 at 22:30 h, together with tadpoles of Bo. shimentaina and Bo. nanlingensis with an ambient air temperature of ~ 20 °C. Two tadpoles at Stages 2627 were collected on 16 November 2021 at 19:30 h with an ambient temperature of ~ 13 °C. Tadpoles were considered nocturnal because we did not encounter any tadpoles during the day. Male Br. popei frogs began their calling activities under rock crevices in this ditch in late July. Zhao et al. (2014) reported that the breeding season of Br. popei is July to September, and that their tadpoles (Stages 26–29) were collected in April and December. This indicates that the development of these tadpoles may be very prolonged, and it is likely that they can over winter. Interestingly, it is unknown why no tadpoles were collected during the breeding season both in this study and in Zhao et al. (2014).

The following description is based on five tadpoles at Stages 25–28 (N = 5). Body ratio ranges represent all specimens. Raw measurements are given in Table 1.

CSUFT T10156 (Stage 25; Field voucher: MT06; GenBank accession number: ON209270) collected on 30 May 2021 from Tiantaishan (24.972277°N, 112.963394°E, ca. 1280 m a.s.l.), Mangshan, Hunan Province, China; and CSUFT T10277 (Stage 26, Field voucher: MT707; GenBank accession number ON209281), CSUFT T10279 (Stage 26; Field voucher: MT709; GenBank accession number: ON209264), CSUFT T10283 (Stage 28, Field voucher: MT713; GenBank accession number: ON209261); and CSUFT T10285 (Stage 27; Field voucher: MT715; GenBank accession number: ON209272) collected on 14 July 2021 from Xiangsikeng (24.937705°N, 112.990257°E, ca. 1530 m, a.s.l.), Mangshan, Hunan Province, China.

The body is oval and flattened above (BW/BL 51.3–55.0%, N = 5); the eyes are located dorsolaterally, and the pupils are round; the nares are oval, open laterally, closer to the eye than to the tip of the snout (NE/SN 62.5–71.4%, IND/IOD 67.6–71.9%, N = 5); the rims of nares are serrated, slightly raised from the body wall; the spiracle is sinistral, low on the left flank; the spiracle tube is short, free from the body at the tip and opens laterally (SS/BL 53.4–58.0%, N = 5); the anal tube opens medially, unattached to the ventral fin; the dorsal fin arises behind the body-tail junction while the ventral fin is connected to the trunk; the tail muscle is massive, taller than tail fins before reaching the 2/3 part of the tail length (TMH/MTH 50.0–55.6%, N = 5); the tail tip is bluntly pointed, the tail length accounts for 69.5–76.1% (N = 4) of the total length; the mouth is terminal and the oral disc is funnel-like (BW/ODW 65.2–77.2%, N = 5); four rows of oval submarginal papillae are visible on the upper lip, and five rows of oval submarginal papillae on the lower lip; keratodonts are absent; the upper jaw sheath is comb-like, exhibiting a small median notch; the lower jaw sheath is thin and sickle-shaped, weakly keratinized, and finely serrated.

The following description is based on a tadpole at Stage 27 (CSUFT T10285). In life, the background color of the body and tail is semi-transparent dark brown; the dorsum is pigmented pale brown which extends to the dorsal surface of anterior tail and gradually becomes golden; a distinct circled marking is present at the center of dorsum, forming a saddle with the background dark brownish coloration; the middle of the saddle is pigmented pale brown; and the neuromasts are distinctly visible. Laterally, the dorsal pattern extends to the region above the horizontal level of the spiracle on the trunk, and covers the whole lateral surface of head; the lateral surface of tail is pigmented brown; the tail and fins are covered with irregularly shaped pale golden spots, interspersed with dense dark brown speckles; the fins are semi-transparent; the anterior part of the dorsal fin is marbled with golden and dark brown speckles; the junction of the anterior half of the dorsal fin and the caudal muscle is pigmented dark brown, forming an incomplete line; the anterior part of the ventral fin and the anal tube exhibit minimal dark brown pigmentation; the posterior part of tail and fins are pigmented with dense dark brown markings. The ventral body is semi-translucent grey, pigmented with dark brown chromocytes, and is covered with dense small, indistinct milky-white speckles; the gills and gut coils are visible through the ventral skin; two large, milky-white spots are present on each side of the ventrolateral surface of head-body connection and are followed by a cluster of smaller spots. The oral disc is translucent milky white; the lateral and middle wings are covered with orangish pigmentation; the tips of the wings and the middle of the upper lip exhibit dark brown pigmentation; the submarginal papillae on lips are dark brown, and the narial rims are pigmented beige. The eye sclera is silver with black dots; the iris is orange sprinkled with black dots; and the spiracle is translucent without pigmentation.

Variation of coloration in life. The other four tadpole specimens match most of the descriptions above. However, the dorsum pattern of a saddle is not clearly visible in CSUFT T10156 and the dorsum is almost uniform pale brown in CSUFT T10177. The ventrolateral spots on head-body connection are very large in CSUFT T10283 (Stage 28, Fig. 2F), but smaller in CSUFT T10277 (Stage 26, Fig. 2E).

Figure 2. 

Boulenophrys shimentaina tadpoles A–C freshly dead tadpole CSUFT T10285 (Stage 27) lateral view, dorsal view, and ventral view D oral disc of tadpole CSUFT T10283 (Stage 28) in life E ventral pattern of tadpole CSUFT T10277 (Stage 26) in life; and F ventral pattern of CSUFT T10283 (Stage 28) in life. E and F share the same scale bar with A–C.

In preserved specimens, the pale brown pigmentation on the dorsal surfaces of the body and tail are still visible; the golden and orangish pigmentation fade to milky white; the white spots on each side of the ventrolateral surface of head-body connection become translucent; there is no orange pigmentation on the mouthparts, and prominent black pigmentation can be observed on the tail.

The two distinct, conspicuous ventrolateral spots on ventrolateral surface of head-body connection could distinguish the tadpoles of Bo. shimentaina from most Boulenophrys tadpoles, including Bo. fansipanensis, which have a single spot visible on each side, and Bo. rubrimera, Bo. hoanglienensis, Bo. jingdongensis, Bo. leishanensis, Bo. jiangi, and Bo. lushuiensis with no ventrolateral spots; the ventral pattern of indistinct, small speckles on belly could distinguish Bo. shimentaina tadpoles from Bo. lini, which have dense large speckles (see Wang et al. 2014: fig. 5F). Furthermore, the tadpoles of Bo. shimentaina differs from Bo. lushuiensis by having a silver sclera with black dots (vs. black with golden pigments); and from Bo. baishanzuensis by having a pale brown pattern on dorsum (vs. uniformly brownish black).

Tadpoles of Bo. shimentaina could be distinguished from the syntopic Boulenophrys tadpoles in Mangshan (see below for the descriptions) by having a dark brown background coloration of body and tail (vs. pale brown in Bo. cf. ombrophila and Bo. nanlingensis), and a tail pattern of dense dark brown markings posteriorly (vs. several large brown spots along tail muscle in Bo. cf. ombrophila; and many brown speckles in Bo. nanlingensis). Further comparisons between Bo. shimentaina tadpoles and all megophryinid tadpoles identified based on molecular data are shown in Tables 2, 3.

A single tadpole at Stage 25 was collected on 30 May 2021, together with the tadpoles of Bo. nanlingensis and Br. popei from the road ditch (Fig. 5C) that was mentioned above in the Br. popei section. Four tadpoles at Stages 25–28 were collected together with tadpoles of Bo. nanlingensis and Bo. cf. ombrophila from a rocky, slow-flowing narrow stream (Fig. 5B) on 14 July 2021 at 23:20 h while nearby adult males were calling. As this stream is located near the mountain top, it is narrow and slow. There were low trees and bamboo on both sides of the stream, and many fallen logs lay across the stream with a rocky stream bed. This site was used by many species as a breeding site including Bo. nanlingensis, Bo. shimentaina, Br. popei, Leptobrachella mangshanensis (Hou, Zhang, Hu, Li, Shi, Chen, Mo & Wang, 2018), and Quasipaa exilispinosa (Liu & Hu, 1975). The tadpoles of Bo. shimentaina found in this stream were observed at night in an area with sandy substrate near the stream bank or in still water behind a small dam formed by submerged leaf litter. Sunlight could reach the surface of these areas at certain times during the day. While feeding beneath the water surface, the tadpoles rely on submerged leaf litter or rocks (Fig. 5A). Once disturbed, they hid quickly under the submerged leaf litter and emerged from the leaf litter after several seconds. In the still water area where these tadpoles were found, we also encountered many Q. exilispinosa tadpoles on the stream substrate, and a subadult newts, Pachytriton xanthospilos Wu, Wang & Hanken, 2012, hiding under submerged leaf litter. Male Bo. shimentaina frogs were observed calling from late June to August in Mangshan, and it was suggested that the breeding season of Bo. shimentaina is from April to August in Shimentai Nature Reserve, Guangdong Province (Lyu et al. 2020). It is not clear if tadpoles complete metamorphosis within a single year, and we didn’t collect any tadpoles of more advanced developmental stages.

The following description is based on four tadpoles at Stages 25–27 (N = 3) and Stage 36 (N = 1). Body ratio ranges represent all specimens except where specified. Raw measurements are given in Table 1.

CSUFT T10992 (Stage 25; field voucher: MT02; GenBank accession number: ON209283) collected on 3 June 2021; and CSUFT T10281 (Stage 26; field voucher: MT718; GenBank accession number: ON209275), CSUFT 10270 (Stage 36, field voucher: MT710; GenBank accession number: ON209267), and CSUFT T10272 (Stage 27, field voucher: MT712; GenBank accession number: ON209269) collected on 14 July 2021. All specimens were collected from Xiangsikeng (24.937705°N, 112.990257°E, ca. 1530 m, a.s.l.), Mangshan, Hunan Province, China.

The body is flattened and oval (BW/BL 52.9–54.8% at Stages 25–27, N = 3; and 51.0% at Stage 36, N = 1); the eyes are located dorsolaterally, the pupils are round; the nares are oval, opening laterally, closer to the eye than to the tip of the snout (NE/SN 60.0–73.3% at Stages 25–27, N = 3; and 82.4% at Stage 36, N = 1); the internarial distance is smaller than interorbital distance (IND/IOD 65.8–68.2% at Stages 25–27, N = 3; and 66.7% at Stage 36, N = 1); the rims of nares are serrated, slightly raised from the body wall; the spiracle is sinistral, low on the left flank, and opens posterolaterally; the spiracle tube protrudes posteriorly, free from the body at the tip (SS/BL 54.9–59.6% at Stages 25–27, N = 3; and 56.0% at Stage 36, N = 1); the anal tube opens medially, unattached to the ventral fin; the dorsal fin arises behind the body-tail junction while the ventral fin is connected to the trunk; the tail muscle is massive, taller than tail fins until reaching 2/3 of the tail length (TMH/MTH 45.8–53.3% at Stages 25–27, N = 3; and 48.3% at Stage 36, N = 1); the tail tip is usually sharply pointed (bluntly rounded in one small-sized specimen CSUFT T10992, Stage 25, TTL 20.9 mm); the tail length accounts for 72.4–75.6% of the total length at Stages 25–27 (N = 3), and 70.3% at Stage 36 (N = 1); the mouth is terminal and the oral disc is funnel-like (BW/ODW 61.5–69.2% at Stages 25–27, N = 3; and 61.4% at Stage 36, N = 1); three and four rows of short oval submarginal papillae are present on the upper and lower lips, respectively; keratodonts are absent; the upper jaw sheath is comb-like, exhibiting a small median notch, whereas the lower jaw sheath is thin and sickle-shaped, weakly keratinized, and finely serrated.

The following description is based on a tadpole at Stage 27 (CSUFT T10272, Fig. 3A–C). In life, the background color of the body and tail is semi-transparent beige; the dorsal surface of the body is covered by a pale brown pattern that extends to the dorsal surface of the anterior part of the tail; a dark spot is present between the eyes and followed by a short beige vertical line on the anterior dorsum; the neuromasts are distinctly visible; and sparse dark brown markings alongside the vertical line and the dorsolateral neuromasts. Laterally, the dorsal pattern extends to above the horizontal level of the spiracle; three large, whitish, and golden pigmented spots are present behind the eyes on each side of the lower part of head-body connection, two of them are visible from the ventral view; the lateral surface of the tail and fins is covered by irregularly shaped pale golden spots, interspersed with whitish chromocytes which form short lines, and brown chromocytes which gather into large spots along the tail muscle at the posterior part of the tail; the fins are semi-transparent; the anterior part of the dorsal fin is marbled with golden and dark brown speckles; the anterior part of the ventral fin and the anal tube exhibit minimal brown pigmentation whereas the rest of fins that exhibits sparse dark brown speckles. The ventral body skin is translucent beige, covered by dense milky white speckles; the gills and gut coils are indistinctly visible through the ventral skin. The oral disc is translucent beige; the lateral and middle wings are covered by orange pigmentation; the submarginal papillae on lips are dark brown; the narial rims are yellow; the eye sclera is silver with black dots; the iris is bright orange sprinkled with black dots; the spiracle is translucent, with scattered golden pigmentation.

Figure 3. 

Boulenophrys cf. ombrophila tadpoles A–C tadpole CSUFT T10272 (Stage 27) lateral view, dorsal view, and ventral view in life D oral disc of tadpole CSUFT T10270 (Stage 36) in preservative E ventral pattern of tadpole CSUFT T10281 (Stage 26) in life; and F ventral pattern of tadpole CSUFT T10270 (Stage 36) in life. E and F share the same scale bar with A–C.

Variation of coloration in life. Among the remaining three specimens examined, two tadpoles at Stages 26 and 36 match most of the coloration pattern of the description for CSUFT T10272 above (see Fig. 3E, F for ventral patterns). However, the dark spot between the eyes is not present in both; the vertical line is more distinct in CSUFT T10281, which extends from the middle of the eyes to the body-tail connection; and the vertical line in CSUFT T10270 is a bit longer than CSUFT T10272, which extend to the posterior dorsum. In the Stage 36 tadpole (CSUFT T10270), the hindlimbs are semi-transparent, and the legs are covered externally by brown chromocytes. A small-sized tadpole at Stage 25 (CSUFT T10992, TTL 20.9 mm) exhibited a significantly different coloration from other three tadpoles of larger body size (Stages 26–27, and 36; TTL 30.4–33.7 mm): the dorsal pattern is pale brown, with scattered dense dark melanocytes, especially at the vertebral line region; an inconspicuous orange V-shaped pattern between the anterior edges of the eyes and the median point of the upper lip; two orangish spots at the posterior edge of the eyes; the orangish pigmentation is also diffuse on the dorsal aspect of the body and tail; the ventral skin is almost clear, translucent milky, with sparse goldish speckles on the edge of the belly; the belly is covered with dense melanocytes, however, gut coils clearly visible through these melanocytes.

In preserved specimens, a fading of the dorsal pattern is observed; the golden spots on the lateral surfaces of the tail are not visible; the large spots on the anterior corner of the spiracle and gills become translucent, and the orange pigmentation on the lips disappears.

The tadpoles of Bo. cf. ombrophila differ from the syntopic tadpoles of Bo. shimentaina by the semi-translucent beige background coloration of body and tail (vs. dark brown), a ventral pattern of dense milky white speckles on belly (vs. indistinct small speckles), and the pattern on tail of large spots along tail muscle (vs. dense markings posteriorly); from Bo. nanlingensis (see below for tadpole description) by the ventral pattern of dense whitish speckles (vs. sparse speckles), and the pattern on tail of several large spots (vs. many speckles).

Compared to other described Boulenophrys tadpoles where species identification is supported with molecular data, the tadpoles of Bo. cf. ombrophila differs by the ventral pattern of dense whitish speckles (vs. relatively sparse metallic blue speckles in Bo. fansipanensis; sparse whitish speckles in Bo. jingdongensis; sparse metallic grey blue speckles in Bo. hoanglienensis; and scattered with silver tiny patches in Bo. lushuiensis), and the tail pattern of several large spots along tail muscle (vs. few dark brown speckles in Bo. fansipanensis; absence of large spots in Bo. jingdongensis; many dark brown speckles in Bo. hoanglienensis; small black spots in Bo. baishanzuensis; few dark spots on posterior tail muscle in Bo. jiangi; small black spots on tail muscle in Bo. leishanensis; and dozens of small dark brown patches in Bo. lushuiensis). Further comparisons between Bo. cf. ombrophila tadpoles and all megophryinid tadpoles that were identified based on molecular data are shown in Tables 2, 3.

One observed breeding site of Bo. cf. ombrophila was a relatively broad wetland crossed by a small shallow creek. Several water sources from the gentle slope of the bamboo forest fed this creek and made the entire area very wet. This breeding site was muddy, covered with leaf litter and fallen logs. The creek was narrow and slow flowing with maximum depth of 0.2 m. Some fallen logs blocked the creek and created still water areas. Only male Bo. cf. ombrophila and Q. exilispinosa were observed calling in this site during our visits from May to August, and in November. The potential predator of these frogs, an aquatic snake Opisthotropis cheni Zhao, 1999 which was observed once, in July, in this creek. A single small-sized tadpole specimen (CSUFT T10992, TTL 20.9 mm) at Stage 25 was collected from this site while the male frogs were heard calling before a heavy rainstorm on 3 June 2021 at 19:30 h at dusk. Three tadpoles were collected from the rocky area (Fig. 5B, mentioned above in the Bo. shimentaina section) 20 m downstream of this creek together with tadpoles of Bo. shimentaina and Bo. nanlingensis. Interestingly, male Bo. cf. ombrophila frogs were not observed calling in the rocky area, and the other two species did not breed in this wetland. This indicates a different microhabitat preference between these congeneric species. The breeding season of Bo. cf. ombrophila ends in mid-July in Mangshan. It is not clear if tadpoles will complete metamorphosis during the year.

The following description is based on 14 tadpoles at Stages 25–29 (N = 12), and 34–35 (N = 2). Body ratio ranges represent all specimens except where specified. Raw measurements are given in Table 1.

CSUFT T10144 (Stage 25; field voucher: MT04; GenBank accession number: ON209279) collected on 30 May 2021; and CSUFT T10302 (Stage 25, field voucher: MT722; GenBank accession number: ON209280), and CSUFT T10303 (Stage 25, field voucher MT723; GenBank accession number: ON209277) collected on 19 July 2021 from Tiantaishan (24.972277°N, 112.963394°E, ca. 1280 m a.s.l.); CSUFT T10261 (Stage 25; field voucher: MT701; GenBank accession number: ON209263), CSUFT T10262 (Stage 25; field voucher: MT702; GenBank accession number: ON209268), CSUFT T10273 (Stage 28, field voucher: MT703, GenBank accession number: ON209278), CSUFT T10991 (Stage 27; field voucher: MT711; GenBank accession number: ON209265), and CSUFT T10284 (Stage 25, field voucher: MT714; GenBank accession number: ON209271) collected on 14 July 2021; and CSUFT T10986 (Stage 35, field voucher: MT1106; GenBank accession number: ON209285) and CSUFT T10969 (Stage 34, field voucher: MT1109; GenBank accession number: ON209274) collected on 19 November, 2021 from Xiangsikeng (24.937705°N, 112.990257°E, ca. 1530 m, a.s.l.); and CSUFT T10376 (Stage 27, field voucher: MT756; GenBank accession number: ON209273), CSUFT T10377 (Stage 27, field voucher: MT757; GenBank accession number: ON209262), CSUFT T10378 (Stage 28, field voucher: MT758; GenBank accession number: ON209282), and CSUFT T10379 (Stage 29, field voucher: MT769; GenBank accession number: ON209266) collected on 28 July 2021 from Guizizhai (24.952750°N, 112.960470°E, ca. 1210 m a.s.l.), Mangshan, Hunan Province, China.

The body is elongated, oval, and flattened above (BW/BL 51.2–60.4% at Stages 25–29, N = 11; and 52.8–54.5% at Stages 34–35, N = 2); the eyes are located dorsolaterally, and the pupils are round; the nares are oval, closer to the eye than to the tip of the snout (NE/SN 55.6–80.0% at Stages 25–29, N = 12; and 57.9–62.5% at Stages 34–35, N = 2); the internarial distance is smaller than interorbital distance (IND/IOD 61.5–71.0% at Stages 25–29, N = 12; and 68.1–69.2% at Stages 34–35, N = 2); the nares open laterally; the rims of nares are serrated, slightly raised from the body wall; the spiracle is sinistral, low on the left flank, and opens posteriorly; the spiracle tube is short and slightly protrudes posteriorly (SS/BL 54.8–62.7% at Stages 25–29, N = 12; and 59.3–63.6% at Stages 34–35, N = 2). The anal tube opens medially and is unattached to the ventral fin; the dorsal fin arises behind the body-tail junction, and the ventral fin is connected to the trunk. The tail muscle is massive, deeper than tail fins before reaching the maximum tail height (TMH/MTH 43.4–63.0% at Stages 25–29, N = 11; and 50.7–54.5% at Stages 34–35, N = 2); the tail tip is pointed, the tail length accounts for 69.5–76.1% (at Stages 25–29, N = 11) and 73.1–74.4% (at Stages 34–35, N = 2) of the total length; the mouth is terminal and the oral disc is funnel-like (BW/ODW 63.3–79.6% at Stages 25–29, N = 12; and 73.1–85.7% at Stages 34–35, N = 2); four and five rows of short oval submarginal papillae can be observed on the upper and lower lips, respectively; keratodonts are absent; the upper jaw sheath is comb-like, exhibiting a weak median notch; the lower jaw sheath is thin and sickle-shaped, weakly keratinized, and finely serrated.

The following description is based on a tadpole at Stage 25 (CSUFT T10303, Fig. 4A–C). In life, the background color of the body and tail are semi-transparent grey; the dorsal surface of the body is covered by a pale brown pattern that extends to the dorsal surface of the anterior part of the tail; roughly symmetrical dark brown pigmentation can be observed on the dorsal body; and the neuromasts are distinctly visible. Laterally, the dorsal pattern extends to above the horizontal level of the spiracle; the lateral surface of the tail is pigmented brown, interspersed with pale golden spots and irregular dark brown speckles; the fins are semi-transparent and scattered with pale golden spots; the anterior part of the dorsal fin is marbled with golden and dark brown speckles, with the dark brown speckles forming an incomplete line; the anterior part of the ventral fin and the anal tube, lacks brown pigmentation but with sparse golden speckles. The ventral surface of the body is semi-transparent grey; the gills appear pink through the ventral skin; two large gold-pigmented white spots are present at ventrolateral head-body connection; the gut coils are distinctly visible through the ventral skin, the belly is scattered with small whitish speckles; the oral disc is translucent beige; the lateral and middle wings are covered by orangish pigmentation; the submarginal papillae on lips are dark brown; the narial rims are beige; the eye sclera is silver with black dots; the iris is copper-colored sprinkled with black dots, comparable to the iris coloration in adults; and the spiracle is translucent.

Figure 4. 

Boulenophrys nanlingensis tadpoles in life A–C tadpole CSUFT T10303 (Stage 25) lateral view, dorsal view, and ventral view D ventral pattern of tadpole CSUFT T10262 (Stage 25) E ventral pattern of tadpole CSUFT T10273 (Stage 28); and F oral disc of tadpole CSUFT T10261 (Stage 25). D and E share the same scale bar with A–C.

Figure 5. 

Megophryinid tadpoles and their habitats in Mangshan, Hunan Province, China (A) Non-collected Bo. shimentaina tadpole (middle) feeding together with two unrecognized tadpoles in its habitat (B); and tadpole habitat (C) of a mixed-species assemblage beside a forest road, with unrecognized tadpoles feeding together (D).

Variation of coloration in life. The dorsal pattern coloration in tadpoles of Bo. nanlingensis is subject to significant variation both in same stages and between stages. At Stage 25, a small-sized tadpole (CSUFT T10144, TTL 18.7 mm) exhibits a yellowish dorsum with pale orange blotches, and dark brown pigmentation present posteriorly; another small tadpole (CSUFT T10284, TTL 18.9 mm) displays a brown dorsum with whitish patterns on the dorsolateral surfaces of the trunk and these extend to the tip of the tail. The coloration of the medium-sized tadpoles at Stage 25 (CSUFT T10261, TTL 25.1 mm; and CSUFT T10262, TTL 27.2 mm) and a broken-tailed individual at Stage 25 (CSUFT T10302) correspond to the dorsal pattern of CSUFT T10303 described above. However, the shape and coverage of dark brown markings varies between individuals. At later Stages 27–29, three medium-sized tadpoles (CSUFT 10377, Stage 27, TTL 28.1 mm; CSUFT T10376, Stage 27, TTL 24.8 mm; and CSUFT 10378, Stage 28, TTL 26.9 mm) exhibit a bi-colored dorsum, which is anteriorly pale brown and posteriorly inconspicuous dark brown. Tadpoles with relatively larger size at both early Stages 27–28 and advanced Stages 34–35 (CSUFT T10273, Stage 28, TTL 35.7 mm; CSUFT T10991, Stage 27, TTL 39.1 mm; CSUFT T10986, Stage 35, TTL 40.1 mm; and CSUFT T10969, Stage 34, TTL 34.4 mm) exhibit a uniform brownish dorsum coloration with almost invisible markings. Two tadpoles, CSUFT T10144 (Stage 25, TTL 18.7 mm) and CSUFT T10379 (Stage 29, TTL 27.8 mm) exhibit pale yellowish dorsum with orange pigmentation, which are indistinguishable from the small-sized Bo. cf. ombrophila tadpole (CSUFT T10992, TTL 20.9 mm). A tadpole at Stage 27 (CSUFT T10376, TTL 24.8 mm) with a mid-vertical line on dorsum is similar with that of larger Bo. cf. ombrophila tadpoles (Stages 26–27, and 36; TTL 30.4–33.7 mm). However, they were not collected form the same site as Bo. cf. ombrophila tadpoles. A large-sized tadpole at Stage 35 (CSUFT 10986, TTL 40.1 mm) showed a ventral pattern of large spots on belly that was different with other specimens. For tadpoles at Stages 34–35 (CSUFT T10969, and CSUFT T10986), the hindlimbs are semi-transparent, the outer aspect of the legs is pigmented yellow and interspersed with brown chromocytes on top.

In preserved specimens, a fading of the dorsal pattern is observed; the tail is translucent with sparse dark-brown pigmentation; the orange pigmentation on lips is no longer visible; the whitish speckle on the ventral surface and the nares are translucent.

The variation of dorsum pattern makes the tadpoles of Bo. nanlingensis are sometimes confused with the syntopic tadpoles of Bo. cf. ombrophila. Usually, the ventral pattern of sparse speckles (vs. dense speckles) and the tail pattern of many small speckles (vs. large spots) could distinguish them. An exception is the small-sized tadpole CSUFT 10144 (Stage 25, TTL 18.7 mm), which bears almost the same pattern as a small-sized Bo. cf. ombrophila tadpole CSUFT T10992 (Stage 25, TTL 20.9 mm). The tadpoles of Bo. nanlingensis differ from the syntopic Bo. shimentaina tadpoles by the pale brownish background coloration of the body and tail (vs. dark brown), the ventral pattern of sparse speckles (vs. dense small speckles), and the tail pattern of small dots (vs. large speckles).

Compared to other described Boulenophrys tadpoles where species identification is supported by molecular data, the tadpoles of Bo. nanlingensis differs by the presence of ventrolateral spots on each side of head-body connection (vs. absent in Bo. jingdongensis, Bo. hoanglienensis, Bo. leishanensis, and Bo. lushuiensis); the tail pattern of many brown speckles (vs. small spots on tail muscle in Bo. leishanensis; few dark spots on posterior tail muscle in Bo. jiangi; and small white and black dots in Bo. baishanzuensis). Further comparisons between Bo. nanlingensis tadpoles and all megophryinid tadpoles that were identified based on molecular data are shown in Tables 2, 3.

Tadpoles of Bo. nanlingensis were discovered in all collection sites during our field surveys in 2021, which perhaps implies that this species has larger population size, or it might exhibit less microhabitat specificity. Besides the three sites mentioned above, four Bo. nanlingensis tadpoles were collected from a relatively wide stream (3–5 m wide), with a maximum depth of 0.5 m. An adult male was observed calling under rocks near the stream bank with its feet standing in shallow water on 28 July 2021.

The male calling activities of Bo. nanlingensis, which began in late July, had increased during our visit in November in Mangshan. It seems the newborn larva would have to over-winter. Thus, we suspected the tadpoles of early Stages 25–29 collected in May and July were born in the previous year. Two tadpoles at advanced Stages 34–35 were collected on the 19^th of November. Considering tadpoles in late stages develop relatively fast (Grosjean, 2003; TQ, personal observation). It was likely these advanced tadpoles would finish metamorphosis in cold season at the beginning of the next year. However, this assumption needs further confirmation because the cold weather and scarce food in winter may not be suitable for the survival of froglets.