AmphibiaWeb - Hynobius ikioi


(Translations may not be accurate.)

Hynobius ikioi Matsui, Nishikawa & Tominaga, 2017
Amber-colored salamander; Bekko-sansyou-uwo
Subgenus: Hynobius
family: Hynobiidae
subfamily: Hynobiinae
genus: Hynobius
Species Description: Matsui M, Nishikawa K, Tominaga A 2017 Taxonomic relationships of Hynobius stejnegeri and H. yatsui, with description of the amber-colored salamander from Kyushu, Japan (Amphibia: Caudata). Zoological Science 34:538-545.
Conservation Status (definitions)
IUCN Red List Status Account Vulnerable (VU)
National Status Vulnerable
Regional Status Vulnerable



View distribution map in BerkeleyMapper.

The head and body of Hynobius ikioi are large and slender. The snout-vent length ranged from 69.0 - 93.2 mm in males, averaging 81.0 mm, and 79.9 - 93.0 mm in females, averaging 86.5 mm. The head is oval-shaped and moderately depressed. The head is distinctly longer than it is wide, and the snout is rounded, projecting slightly beyond the lower jaw. The nostrils of H. ikioi are close to the snout tip, and the labial fold is absent. The eye is large and prominently protruded, and is slightly inset from the edge of the head in the dorsal view. The upper eyelid is well developed, and shorter than the snout. The postorbital grooves are distinct, and branch posterior to the angle of the jaw; one is short and runs down to the lower jaw, and the other is long and located posterior to the parotid gland. The parotid gland is evident, and extends from the angle of the jaw to the gular fold. The gular fold is distinct, curving slightly anteriorly (Matsui et al. 2017)

The forelimbs are long and thin, and the relative finger lengths are I < IV < II < III. The forelimbs and hind limbs are separated by one costal fold, of which there are 13 - 14 costal grooves. The hind limbs are also long and thin, and the relative toe lengths are I < V < II < IV < III. The fifth toe is well developed, and is relatively long for the genus (Matsui et al. 2017).

The cloaca has a longitudinal slit, and there is a genital tubercle present on the anterior cloaca. The tail is long, and cylindrical at its base, but is slightly compressed posteriorly. A dorsal fin is evident on the posterior portion of the tail, and the tip of the tail is rounded in the lateral view (Matsui et al. 2017).

In late stage larvae, in early July of their first year, the snout-vent length averaged 20.5 mm. Two larvae in mid-September had snout vent lengths of 25.0 and 26.6 mm. Overwintered larvae in early May of the second year had an average snout-vent length of 26.3 mm. The snout-vent length of metamorphosing larvae in early May of the second year was on average 29.9 mm, and for two metamorphosing individuals in mid September, the snout-vent lengths were 33.3 and 35.0 mm. The head of larval Hynobius ikioi in the dorsal view is trapezoidal, and greatly depressed and sloping in profile. The snout of larval H. ikioi is long and slightly truncated. The eyes are slightly protruded and inset from the edge of the head in dorsal view. Its labial fold is distinct at the posterior two-thirds of the upper jaw. The external gills are well developed. The limbs of larval H. ikioi are robust, and there are claws present on all fingers and toes. The dorsal caudal fin is slightly higher than the head and deeper than the ventral fin. The origin of the dorsal fin is at the middle to posterior one-third of the trunk. The ventral fin originates from the vent. The tip of the tail is moderately pointed (Matsui et al. 2017).

Adult H. ikioi have a decidedly larger body than H. stejnegeri. In males, H. ikioi has a much larger snout-vent length than H. amakusaensis, H. osumiensis, H. stejnegeri, and H. naevius, and shorter forelimbs than H. shinichisatoi. Hynobius ikioi also has longer fingers and toes than H. boulengeri. Hynobius ikioi has a better-developed fifth toe, compared to the much smaller fifth toe length of H. stejnegeri. The tail of H. ikioi is longer than its congeners, and although the medial tail width and height does not differ much from H. stejnegeri, the tail is compressed posteriorly, unlike in H. stejnegeri. Hynobius ikioi has deeper vomerine tooth series than H. hirosei. Male H. ikioi also have a narrower vomerine tooth series than H. shinichisatoi. The ground color of H. ikioi is blackish brown, which is very different than the light reddish-purple body color of H. stejnegeri, slate-colored or purplish brown H. shinichisatoi and H. osumiensis, and the bluish or reddish-purple ground color of H. naevius. The markings of H. ikioi are amber colored on its dorsal side, as opposed to H. amakusaensis, which has white markings, H. stejnegeri, which has small pale-white markings, H. naevius, which have white lateral markings, and H. shinichisatoi and H. osumiensis, which have no markings at all (Matsui et al. 2017).

In life, the dorsum of adults is jet-black and scattered with orange-yellow blotches. The underside of H. ikioi is lighter than the dorsum, and is sparsely marked with light blotches. The iris of H. ikioi is dark brown, and has no markings. In preservative, the light blotches on the underside of H. ikioi tend to fade and become whitish. Otherwise, there was no obvious change from color in life (Matsui et al. 2017).

For the larval form of H. ikioi, in life, the dorsum is dark brown and usually has a beige stripe. The venter is whitish and transparent. There are large black spots all over from head to tail with the exception of the ventral side. There are golden dots scattered on the tail fin. The claws are all black. In preservative, the dorsal coloration tends to fade, becoming light brown. The golden dots also fade to white (Matsui et al. 2017).

There appears to be some sexual dimorphism in H. ikioi. Males had an overall smaller snout-vent length than females, and also tended to have fewer costal grooves than females with males tending to have 13 and females tending to have 14. Development of the tail fin was only found in breeding males. In life coloration varies individually, from completely jet-black with no markings, to densely mottled with orange-yellow markings on the dorsum. Juveniles have their dorsum scattered with silver dots (Matsui et al. 2017).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan


View distribution map in BerkeleyMapper.
At the time of description, Hynobius ikioi was only known from Kumamoto, Miyazaki, and the northern part of Kagoshima prefectures, Japan. Hynobius ikioi is found in narrow ranges of broad-leaf deciduous or mixed forests along the Kyushu mountain ridge south of the Median Tectonic Line, and south of the Aso mountain, but north of the Kirishima mountains. Hynobius ikioi is found in ranges from 250 to 1500 m in altitude (Matsui et al. 2017).

Life History, Abundance, Activity, and Special Behaviors
Hynobius ikioi inhabits headwaters of small streams, about 0.5 - 2.0 m in width, in deeply covered forests of broad-leaf deciduous trees or mixed forests, but it does inhabit evergreen broad-leaf forests at the southern limit of its distribution (Matsui et al. 2017).

The breeding season of H. ikioi is from early April to early May, with the peak in late April. Breeding occurs in shadowy waters downstream of headwaters, that are covered by rotten woods or rocks, where the bottom consists of sand and small rocks (Matsui et al. 2017).

Egg sacs are laid under stones in the water. The egg sacs are string-like in shape. They coil two and a half times with a thin envelope lacking notable striations and any distinct whiptail structure. The length of the egg sac ranges from 100 - 300 mm and the width ranges from 9 - 20 mm. The clutch size ranged from 21 - 57 eggs, averaging 36. From two female individuals, the diameters of the ova were 4.2 and 5.2 mm. Both the animal and the vegetal poles are cream-colored (Matsui et al. 2017).

Hatched larvae appear in May, and metamorphose from July to September. However, some larvae will overwinter in the water and metamorphose in April of the next year (Matsui et al. 2017).

In captivity, females sexually mature 4 years after metamorphosis (Matsui et al. 2017).

Larvae feed on amphipods, larval caddisflies, mayflies, and each other. Metamorphosed individuals feed on spiders, insects, earthworms, and other small invertebrates (Matsui et al. 2017).

Hynobius ikioi and H. stejnegeri sometimes occur syntopically, but they have completely separate breeding sites and larval habitats (Matsui et al. 2017).

Trends and Threats
In 2000, when Hynobius ikioi was still under the name of Hynobius stejnegeri, it was listed as “Vulnerable" on the IUCN Red List (Matsui et al. 2017). As of 2004, this listing is still “Vulnerable.” Hynobius ikioi is threatened by hunting, trapping, logging, and wood harvesting. Major threats also include road construction, deforestation, erosion, and pollution. There is movement to raise awareness about the decline and extent of their habitats in Japan (Kaneko and Matsui 2004).

Relation to Humans
Hynobius ikioi is often hunted for food and medicine, especially in the medicinal field of comparative hepatology. In its native Kumamoto prefecture, H. ikioi is a designated natural monument, indicating its importance to the prefecture (Matsui et al. 2017).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intentional mortality (over-harvesting, pet trade or collecting)

The species authority is: Matsui, M., Nishikawa, K.,Tominaga, A. (2017). “Taxonomic relationships of Hynobius stejnegeri and H. yatsui with description of the amber-colored salamander from Kyushu, Japan (Amphibia: Caudata).” Zoological Science 34(6):538-545

Genetic analysis was done on the cyt b mitochondrial gene using Bayesian Inference (Nishikawa and Matsui 2014). The genetic analysis revealed a clade consisting of H. ikioi, H. amakusaensis, and H. osumiensis, with H. shinichisatoi as the sister species. The divergence at the cyt b gene of H. ikioi to H. amakusaensis was extremely small (2.9%), but the recognition of their different species relationship should be maintained, since they are completely isolated by the Ariake Sea as well as clear morphological evidence. Analysis of the LDH-B and sAAT-A allozymes further supported the separate-species classification (Matsui et al. 2017).

The name “ikioi” is dedicated to the late Professor Ikio Sato of Hiroshima Bunrika University (now Hiroshima University), who made great contributions to the study of Japanese tailed amphibians, but who unfortunately died in the atomic bomb attack on Hiroshima (Matsui et al. 2017).

Prior to its description, the amber-colored salamander was commonly and incorrectly referred to as H. stejnegeri, a small species of the H. naevius complex. The taxonomy is further complicated as another small species, called H. yatsui, was revealed to be a junior synonym to H. stejnegeri and has now been relegated to the former. After reexamination of H. stejnegeri and H. yatsui, it was found that they could not be differentiated morphologically, strongly suggesting their conspecificity. However, the amber-colored salamander that is the topic of this account, H. ikioi, differs greatly from the true H. stejnegeri (including H. yatsui). The name H. stejnegeri now applies to the species was previously named H. yatsui, while H. ikioi refers to the populations formerly known as H. stejnergeri from northern Kagoshima prefectures (Matsui et al. 2017).


Kaneko, Y., Matsui, M. (2004). Hynobius boulengeri. The IUCN Red List of Threatened Species 2004: e.T59091A11869929. Downloaded on 22 February 2017.

Matsui, M., Nishikawa, K., Tominaga, A. (2017). ''Taxonomic relationships of Hynobius stejnegeri and H. yatsui, with description of the amber-colored salamander from Kyushu, Japan (amphibia: caudata).'' Zoological Science, 34(6)(538-545), 8. [link]

Nishikawa, K., Matsui, M. (2014). ''Three new species of the salamander genus Hynobius (Amphibia, Urodela, Hynobiidae) from Kyushu, Japan.'' Zootaxa, 3852(2), 203-226.

Originally submitted by: Alice Drozd (first posted 2020-10-14)
Edited by: Ann T. Chang (2020-10-14)

Species Account Citation: AmphibiaWeb 2020 Hynobius ikioi: Amber-colored salamander; Bekko-sansyou-uwo <> University of California, Berkeley, CA, USA. Accessed Dec 11, 2023.

Feedback or comments about this page.


Citation: AmphibiaWeb. 2023. <> University of California, Berkeley, CA, USA. Accessed 11 Dec 2023.

AmphibiaWeb's policy on data use.