Hynobius akiensis Matsui, Okawa et Nishikawa, 2019

Tomimori, Yusuke, Matsui, Masafumi, Okawa, Hiroshi, Nishikawa, Kanto, Tanabe, Shingo & Kamasaka, Ryo, 2023, Reassessment of species delimitation using nuclear markers in three lentic-breeding salamanders from the Chugoku District of Japan (Amphibia: Caudata: Hynobiidae), Zootaxa 5293 (1), pp. 145-160 : 156-157

Hynobius akiensis Matsui, Okawa et Nishikawa, 2019

Hynobius abei (part) Sato, 1943, 163.

Hynobius nebulosus (part, as Transitional morphotype) Okawa and Utsunomiya, 1992, 12. Hynobius nebulosus (part, as Miyoshi morphotype) Okawa and Utsunomiya, 1992, 12.

Hynobius nebulosus (part, as Aki morphotype) Okawa et al., 2005, 11

Holotype KUHE 35925 , from Haizuka, Mirasaka-cho, Miyoshi-shi , Hiroshima Prefecture.

Paratype KUHE 35924 , one male, data same as the holotype. ( KUHE 8682–8687 from Kurose-cho, Higashihiroshima-shi, in the original description ( Matsui et al. 2019 removed.)

Specimens referred in the present paper. Hiroshima Prefecture: Akitakata-shi , KUHE OU 0313 , 0314 , from the former Mukaihara-cho , collected by H. Okawa on 15 April 2007 . KUHE OU 0368 , 0369 , from Takamiya-cho , collected by H. Okawa on 26 April 2009 . KUHE OU 0510 , from Takamiya-cho , collected by H. Okawa on 2 May 2010 . KUHE 58834 , from the former Koda-cho , collected by Y. Misawa on 1 March 2017 . Higashihiroshima-shi , KUHE OU 0309–0312 from the former Toyosaka-cho , collected by H. Okawa on 5 April 2007 . KUHE OU 0905 , 0907 , from the former Fukutomi-cho , collecter by H. Okawa on 4April 2017 . Miyoshi-shi , KUHE OU 0301–0303 , from the former Miwa-cho , collected by H. Okawa on 28 March 2007 . KUHE OU 0387–0389 , from Miwaka-cho , collected by H. Okawa on 3 March 2010 . KUHE OU 0390 , from Shimoshiwachi-cho , collected by H. Okawa on 3 March 2010 . KUHE 58887 , 58888 , from Mirasaka-cho , collected by Y. Misawa on 7 March 2018 . KUHE OU 0970–0972 , from Miwaka-cho , collected by H. Okawa on 8 April 2019 . KUHE 61385 , 61385 _1, 61385_2, from Miwaka-cho , collected by H. Okawa on 5 Jury 2019 . KUHE 62661–62664 , from Megurikami-cho , collected by Y. Tomimori on 16 February 2021 . Kitahiroshima-cho , Yamagata-gun , KUHE 61220 , 61220 _1, 61220_2, collected by Y. Tomimori on 19 Jury 2019. Sera-cho, Sera-gun , KUHE OU 0472 , from Sera-cho , collected by H. Okawa on 13 March 2010 . KUHE OU 0474 , from Sera-cho , collected by H. Okawa on 19 March 2010 . KUHE OU 0479 , from the former Seranishi-cho , collected by H. Okawa on 19 March 2010 .

Diagnosis. A small species of the genus Hynobius that breeds in wetlands in hilly to mountainous areas about 1000 m. altitude (adult male SVL 40.8–57.5 mm). Phylogenetically, H. akiensis forms a clade with H. geiyoensis and H. sumidai in nuclear DNA, which relationships not supported by mtDNA. Dorsum dark brown, some almost dark blue. Yellow stripes on upper and lower edges of tail indistinct. Limbs and tail short, forelimb and hindlimb tips barely meeting (overlap of -2 to 0.5 costal folds in males). Fifth toe least developed in H. akiensis sensu lato (R5TL: H. akiensis 1.8%, H. sumidai 2.0%, and H. geiyoensis 2.7%). Egg sac short, loosely coiled into a string, with smaller clutch size than in other lentic breeding species of the genus. Most similar to H. sumidai but with wider internarial (RIND 6.3% vs. 5.7%), interorbital (RIOD 6.4% vs. 6.0%), and longer forelimbs (RFLL 25.3% vs. 23.6%) and hindlimb (RHLL 30.8% vs. 29.5%).

Color. In life, dorsum yellowish brown with minute black spots. Dark blue or dark brown individuals without black spots also present. Small white spots on ventral side, and often indistinct yellowish-brown stripe on dorsal edge of tail, less distinct on ventral side. In preservative, ventral color tends to be faded to grayish brown and white nuptial color on throat not clear.

Variation. Morphological measurement data for males are summarized in Table 2 . In 27 males examined, SVL 48.8 ± 4.4 (40.8–57.5) mm, adpressed limbs always separated, fifth toe generally weakly developed, some individuals with only four toes (about 15% of the specimens examined). Body color light brown with black spots, some individuals with silvery white spots on dark brown and dark blue background.

Range. Hiroshima Prefecture: Akitakata-shi (including the former Yoshida-cho, Mukaihara-cho, Koda-cho, Takamiya-cho, Yachiyo-cho and the former Midori-cho [Sugahara et al. 2022]); Higashihiroshima-shi (including the former Fukutomi-cho, Toyosaka-cho); Mihara-shi (including the former Daiwa-cho, and the former Kui-cho [Sugahara et al. 2022]); Onomichi-shi (including the former Mitsugi-cho); Miyoshi-shi (including the former Kisacho, Mirasaka-cho, Miwa-cho); Kitahiroshima-cho, Yamagata-gun (including the former Chiyoda-cho, Oasa-cho, and the former Toyohira-cho, and Geihoku-cho [Sugahara et al. 2022]); Sera- cho, Sera-gun (including the former Seranishi-cho); Hiroshima-shi (only former Asakita-ku [Sugahara et al. 2022]); Akiota-cho (only former Togochicho [Sugahara et al. 2022]). Shimane Prefecture: Onan-cho (only former Mizuho-cho and Hasumi- mura [Sugahara et al. 2022]). Altitude of the localities extends from 260.0– 930.0 m with the mean±SD of 447.9± 145.4 m (n=23).

Natural history. Breeding usually occurs in hilly streams, wetlands, and paddy ditches from March to April. Egg sacs are string-like in shape and coiling. number of eggs is 24.5 ± 8.6 (2–58) ( Okawa et al. 2019). The minimum and maximum water temperatures at the time of breeding were 2.5–5.0°C and 8.1–11.1°C, respectively in Haizukadam, Mirasaka-cho, Miyoshi-shi, Hiroshima Prefecture. ( Utsunomiya et al. 1996).

Morphological Comparisons. Hynobius akiensis has a dark brown body color with small black dots on dorsal side and small white spots on ventral side, a body color pattern that is often seen in lentic Hynobius (e.g., H. sumidai , H. akiensis , H. setouchi , H. utsunomiyaorum , H. abuensis , H. iwami , H. bakan , H. setoi , and H. kunibiki ). However, H. iwami , H. bakan , H. setoi , and H. kunibiki can be distinguished from H. akiensis because they have a distinct yellow stripe on dorsal and ventral sides of tail, while H. akiensis has an indistinct yellow stripe on dorsal side if present. Hynobius akiensis and H. iwami may be confused because of their close distribution and tendency of lacking the fifth toe.

Hynobius akiensis (mean male SVL 48.8 mm) H. abuensis (57.3 mm). Hynobius akiensis significantly differs from H. setouchi in the following ratio values: shorter maximum head width, tail length, medial tail height, third toe and fifth toe, and smaller vomerine teeth series. Hynobius akiensis is distinguishable from H. utsunomiyaorum by its significantly smaller SVL and following ratio values: larger head, longer lower jaw, larger eyes, shorter axilla-groin distance and medial tail width, higher basal tail, longer hindlimb, third finger and fifth toe, and larger vomerine teeth series. Hynobius akiensis significantly differs from H. iwami in the following ratio values: shorter upper eyelid length, higher basal tail, and longer fifth toe. Morphological differences from allied species H. sumidai and H. geiyoensis are noted above for each species.

Protection. H.akiensis is in the Japanese Red List as Endangered ( EN) (Ministry of the Environment Government of Japan 2020). This species is on the list of Hiroshima Prefecture as

Vulnerable (VU) by the Red Data List Hiroshima ( Okawa 2021), and on the list of Shimane Prefecture as Near Threatened (NT) by the Revised Shimane Red Data Book 2014 Animals ( Akiyoshi and Matsuno 2014).