Description

DESCRIPTION: (A description of species morphology as if you had the amphibian in your hand, typically starting with the snout-vent length, then focusing from the head to the body and extremities)

Hynobius bakan is a medium-sized lentic salamander with a male snout-vent length of 44.0 - 56.5 mm and a female snout-vent length of 50.2 - 56.9 mm, based on 14 males and 5 females. The head is ovular and it is longer than it is wide. The snout appears rounded, somewhat protruding beyond the lower jaw. The nostrils are close to the snout tip. There is no labial fold. In dorsal view, the eye is somewhat inset. The upper eyelid is well-developed. The gular fold is present and the parotid gland is evident, running from the jaw angle to the gular fold. Postorbital grooves are present, extending from the jaw angle, with one running to the lower jaw and the other to the posterior of the parotid gland. The fore- and hind limbs are thick, with forelimb length being shorter than the hind limb length. There are 13 costal grooves with about -1.0 to 1.5 grooves between adpressed limbs. The relative finger length formula is I < IV < II < III and the relative toe lengths are I < V < II < III < IV. The tail is 55.8% - 76.6% of the snout-vent length in males and 63.9% - 80.8% of the snout-vent length in females. It is cylindrical at the base, gradually compressing toward the posterior. A weak dorsal fin is present near the tail tip (Matsui et al. 2019, Sugawara et al. 2022).

DIAGNOSIS: (How this species is differentiated from similar species)

Compared to H. nebulosus, which H. bakan was described from, H. bakan has a shorter average snout-vent length (51.7 mm in H. bakan compared to 59.3 in H. nebulosus) (Matsui et al. 2019). Hynobius nihoensis and H. nagatoensis are both described from populations previously thought to be of H. bakan (see Comments). Hynobius bakan, H. nihoensis, and H. nagatoensis can most easily be distinguished by the number of costal grooves between adpressed limbs. The number of costal grooves between limbs for H. bakan is -1.0 to 1.5 in males and -2.0 to 0.0 in females; in H. nihoensis this is -4.5 to -1.5 for males and 4.5 to -2.5 for females; and -1.0 to 1.5 in H. nagatoensis males and -2.0 to 0.0 in H. nagatoensis females. Hynobius bakan has a larger head width to snout-vent length ratio in both males and females compared to H. nihoensis. For H. bakan, this ratio is generally 17% or higher in males and 16.5% or higher in females. Hynobius nihoensis males usually have a head to snout-vent length ratio below 17% and below 16.5% for females (Sugawara et al. 2022).

COLORATION: (In life and/or in preservative)

In life, the dorsum is dark brown with black markings scattered throughout, while the venter is lighter than the dorsum and has silvery dots (Matsui et al. 2019). Dorsal coloration can range from yellowish- to blackish-brown. The venter can be bluish-white, reddish-white, or whitish-indigo. The iris ranges from dark to light brown. Yellow stripes on the tail range from clearly to weakly visible. In preservative, the dorsum fades to dark gray (Sugawara et al. 2022).

VARIATION: (if known)

Many males have white nuptial coloring. The fifth toe is almost always present, with some individuals only having a rudimentary one (Matsui et al. 2019). Males generally have a longer head length, head width, tail length, forelimb length, and hind limb length than females. Females rarely have black spots on the dorsum. Males usually lack white spots on the venter. Males often lack bright yellow lines on the dorsum while most females have them. Males often have bright yellow lines on the venter and often lack distinct gular mottling (Sugawara et al. 2022)

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

View distribution map in BerkeleyMapper.

The species ranges from southwest Yamaguchi Prefecture in the Chugoku region of Honshu, Japan, to Oita Prefecture in northeastern Kyushu, Japan. The species occupies elevations between 15 and 280 m (IUCN 2021).

Life History, Abundance, Activity, and Special Behaviors
Breeding occurs between January and early April, with egg sacs being deposited in marshes, ditches, pools, abandoned rice paddies, ponds, and slowly-flowing streams. The egg sac coils and has a string-like shape. The envelope is thin and wrinkled, lacking striations or a whiptail structure. Egg sac lengths range from 106 - 194 mm (averaging 145.9 ± 31.0 mm), and their widths range from 14.7 - 17.8 mm (averaging 16.2 ± 1.1 mm). Clutch size ranges from 56 – 333 (averaging 116.5 ± 58.2). The animal pole is dark brown and the vegetal pole is lighter brown (Matsui et al. 2019).

Trends and Threats
The abandonment and desiccation of rice paddies threatens H. bakan populations. Deforestation and urbanization also threaten H. bakan in addition to overcollection. Due to habitat fragmentation and small population sizes, H. bakan populations are unsustainable and decreasing (IUCN 2021, Matsui et al. 2022).

Relation to Humans
Hynobius bakan are collected as pets nationwide. All H. bakan pets are captured from the wild (IUCN 2021).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Urbanization

Comments

Hynobius nebulosus was previously thought to be one widespread species across western Japan. Maximum Likelihood analysis and Bayesian inference of cytochrome b mtDNA revealed that it actually consisted of nine species, two of which include H. nebulosus and H. vandenburghi, while the other seven were described as new species, including H. bakan (Matsui et al 2019).

Since its description, H. bakan has been further divided into three groups using Maximum Likelihood analysis and Bayesian inference of cytochrome b mtDNA, alongside morphological analysis: the Yamaguchi group, the Usa-Bungotakada population of the Oita group, and the Ube population of the Oita group (the Oita group includes three genetic clades: the Ube, Onoda, and Usa-Bungotakada populations.) The Usa-Bungotakada population of the Oita group was described as H. nagatoensis and the Yamaguchi group was described as H. nihoensis. Based on this study, H. bakan forms a monophyletic group with H. nihoensis. The next most closely related clade is H. nagatoensis, and the clade formed by these three species is sister to H. dunni (Sugawara et al. 2022).

ETYMOLOGY (Origin or explanation of scientific name):

The species epithet “bakan” comes from the old name of Shimonseki in Yamaguchi Prefecture, which is where the species occurs (Matsui et al. 2019).

References
IUCN SSC Amphibian Specialist Group. (2021). Hynobius bakan. The IUCN Red List of Threatened Species 2021: e.T149661429A175920827. https://dx.doi.org/10.2305/IUCN.UK.2021-1.RLTS.T149661429A175920827.en. Accessed on 05 September 2023.

Matsui, M., Okawa, H., Aoki, G., Eto, K., Yoshikawa, N., Tanabe, S., Misawa, Y., and Tominaga, A. (2019). Systematics of the widely distributed clouded salamander, Hynobius nebulosus (Amhibia: Caudata: Hynobiidae) and its closest relatives. Current Herpetology 38(1), 32-90. [link]

Sugawara, H., Tahara, Y., Nakazono, S., Matsukoji, T. and Nagano, M. (2022). Taxonomic revision of the Yamaguchi Salamander Hynobius bakan: Description of two new species from Chugoku and Kyushu, Japan. Science Report of the Yokosuka City Museum 69, 1–17. [link]

Species Account Citation: AmphibiaWeb 2023 Hynobius bakan: Yamaguchi salamander <https://amphibiaweb.org/species/8977> University of California, Berkeley, CA, USA. Accessed Apr 29, 2025.

Citation: AmphibiaWeb. 2025. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 29 Apr 2025.

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