Hynobius sumidai, Sugawara & Naito & Iwata & Nagano, 2022

Sugawara, Hirotaka, Naito, Jun-ichi, Iwata, Takayuki & Nagano, Masahiro, 2022, Molecular Phylogenetic and Morphological Problems of the Aki Salamander Hynobius akiensis: Description of Two New Species from Chugoku, Japan, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 51, pp. 35-46 : 42-44

Hynobius sumidai sp. nov.

(New standard Japanese name: Hiroshima-sanshouo)

( Figs. 4–5)

Hynobius nebulosus : Okawa et al., 1990: 50, in part. Hynobius akiensis Matsui, Okawa and Nishikawa in

Matsui et al., 2019: 75, in part.

Etymology. The specific name “ sumidai ” is dedicated to Dr. Masayuki Sumida who was the phylogenetic taxonomist of amphibians at Hiroshima University.

Holotype. An adult male (specimen number: HMNH- AM-102) from Tamaricho , Takehara-shi, Hiroshima Prefecture, Chugoku, Japan [34° 24′ N, 132° 47′ E; elevation = 340 m above sea level (a.s.l.); in all cases, datum = WGS84], collected by Jun-ichi Naito on 23 March 2021.

Paratype. An adult female (specimen number: KPM-NFA 945 ) from the same locality of the holotype, collected by Jun-ichi Naito on 23 March 2021 .

Diagnosis. A comparatively small species (mean snout– vent length of 47.2 mm in males) within the Japanese lentic Hynobius ; SVL usually less than 50 mm; distinct brownish–yellow stripe on the dorsal edge of the tail always present; distinct brownish–yellow line on the ventral side of the tail never present; distinct gular mottling never present; yellowish–brown to blackish–brown on dorsum; the fifth toe of hindlimb always present; V-shaped vomerine teeth series; usually 12 costal grooves (rarely 13); costal folds between adpressed limbs always less than 1.0; coil-shaped egg sacs.

Description of holotype. A moderately large individual with HL larger than HW; TAL shorter than SVL; body almost cylindrical; rounded snout; gular fold present;

tail gradually compressed toward the tip; non-expanded cloaca; webbing between digits absent; four fingers on each forelimb, order of length II > III > I> IV on left and II > III > IV > I on right; five toes on each hindlimb, order of length III > IV > II > I> V on both sides; V-shaped vomerine teeth; skin smooth and shiny; DBDD absent; DWDV and DWDL absent; DTBYLD present (it became unclear after preservation); DTBYLV absent; DGM absent. The holotype had the following measurements (in mm) : SVL = 48.2, TRL = 36.6, AGD = 26.0, HL = 11.3, TAL = 34.6, MTAW = 2.4, MTAH = 4.7, BTAW = 5.4, BTAH = 4.4, VTL = 2.6, VTW = 2.5, HW = 8.0, MXHW = 8.2, LFLL = 11.8, RFLL = 11.9, LHLL = 14.1, RHLL = 14.0, L1 FL = 1.3, L2 FL = 2.1, L3 FL = 1.9, L4 FL = 0.9, R1 FL = 0.7, R2 FL = 1.6, R3 FL = 1.2, R4 FL = 0.8, L1 TL = 1.1, L2 TL = 2.0, L3 TL = 3.3, L4 TL = 2.3, L5 TL = 0.8, R1 TL = 1.3, R2 TL = 1.7, R3 TL = 2.9, R4 TL = 1.9, R5 TL = 0.7, IND = 2.3, IOD = 3.0, LUEW = 1.6, RUEW = 1.4, SL = 3.4, LUEL = 2.4, RUEL = 2.2, LJL = 6.9, and CGN = 12.

Comparisons. The new species statistically differs from H. geiyoensis sp. nov. in the following length measurements: SVL, RHL, RTAL, RFLL, R 3 FL, R 3 TL, R 5 TL, RUEW, and RUEL in males; the lengths of these measurements, except for RHL, RFLL, RUEW, and RUEL, are significantly longer in H. sumidai sp. nov. relative to the measurements in H. geiyoensis sp. nov.. The new species differs from H. geiyoensis sp. nov. by the following characters: SVL <50 mm (7/7 = 100 %) vs. SVL > 50 mm (19/19 = 100 %); R 5 TL <1.9 % (7/7 = 100 %) vs. R 5 TL > 1.8 % (18/19 = 94.7 %); RUEW > 3.1 % (7/7 = 100 %) vs. RUEW <3.2 % (18/19 = 94.7 %); RUEL > 4.3 % (7/7 = 100 %) vs. RUEL <4.3 % (18/19 = 94.7 %). The new species statistically differs from H. akiensis in the following length measurements: SVL (shorter), RVTL (longer), and R 3 FL (shorter) in males. The most distinct characteristic between the two species is the presence of DTBYLD: H. sumidai sp. nov. always has this characteristic (7/7 = 100 %), whereas H. akiensis usually lacks it (25/28 = 89.3 %).

Variation. Morphometric measurements and observations are presented in Tables 2 and 4, respectively. The dorsum is uniformly yellowish–brown or darkish– brown. The venter is lighter than the dorsum. DBDD rarely absent (2/7 = 28.6 %), DWDV and DWDL sometimes absent (3/7 = 42.9 %), sometimes it has 13 CGN (3/7 = 42.9 %), and rarely has more than 0 CFBALN (1/7 = 14.3 %). The iris is dark brown or light brown. When preserved, the dorsal coloration tends to fade to dark gray and DTBYLD becomes unclear after preservation.

Distribution. This new species is endemic to Hiroshima

Prefecture, and it is known from Higashihiroshima-shi (only former Higashihiroshima-shi and Akitsucho) and Takehara-shi. Its distribution is thought to bein the former Kurose-cho and Kure-shi areas, but no supporting evidence is available to confirm this hypothesis. Further phylogenetic studies using more samples from Higashihiroshima-shi and Kure-shi are therefore essential.

Natural History. The dominant vegetation type in the type locality is a mixed forest of evergreen oak ( Quercus spp. ) and Japanese cypress ( Chamaecyparis obtusa ). The larval and egg sac morphologies of this new species are similar to those of H. geiyoensis sp. nov. The breeding season of the new species is February to April.

Remarks. The new species forms a monophyletic group with the Highland and Aki groups ( Matsui et al., 2019). The morphology of females is unclear; hence, additional studies to clarify the morphology of females are needed.