Hynobius oni Kanamori, Nishikawa, Matsui & Tanabe, 2022
Nanyo salamander, Japanese name: Nan-yo-sanshouo
|Species Description: Kanamori S, Nishikawa K, Matsui M, Tanabe S. 2022. A new species of lotic breeding salamander (Amphibia, Caudata, Hynobiidae) from Shikoku, Japan. PeerJ 10:e13891|
Within the Hynobius genus, H. oni resembles H. boulengeri, H. katoi, H. shinichisatoi, H. osumiensis, and H. hirosei due to the uniform dorsal color. Hynobius oni has a smaller body size than H. boulengeri (mean male snout-vent length in H. oni is 79.4 mm while H. boulengeri is 93.9 mm) and H. hirosei (85.5 mm), while it is larger than H. katoi (58.4 mm) and H. osumiensis (68.4 mm). Compared to H. shinichisatoi, H. oni has a shorter tail length (mean tail length of H. oni is 80.4% of snout-vent length while H. shinichisatoi is 90.4%) and shallower vomerine teeth (vomerine teeth width in H. oni is 1.6 mm and 1.2 mm in H. shinichisatoi). Compared to H. hirosei, in addition to a smaller body size, H. oni has a longer axilla-groin distance, shorter tail length, shorter internarial distance, longer upper eyelid length, and larger medial tail width. Based on mtDNA, H. oni is genetically closer to H. sematonotos than H. hirosei. However, H. oni does not have any large body markings and has a longer snout-vent length, while H. sematonotos has silvery spots and a shorter snout-vent length (Kanamori et al. 2022).
In life, the adult dorsum is uniformly dark reddish brown and immaculate with no markings. The ventral side is lighter than the dorsum and the underside of the tail is somewhat ochre. The iris is a solid dark brown. In preservatives, there are no obvious changes to the coloration besides the dorsal side fading and becoming gray-brown (Kanamori et al. 2022).
All specimens have generally similar body size and proportions. The dark reddish-brown adult dorsal color may be less red or darker. Young individuals have white dots scattered on the dorsum. The one female paratype, with a snout-vent length of 84.6 mm, is as large as the male holotype, with a snout-vent length of 82.7 mm. However, the female’s upper eyelid width is smaller than that of the twelve male specimens (3.1% of the snout-vent length for the female and 3.2 - 3.8% in males). The female paratype’s tail is also lower and thinner (Kanamori et al. 2022).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
The breeding season is assumed to be in late April as egg sacs have been found under rocks in streams in late April. The ova are large and pigmentless. The long, crescent-shaped egg sacs have a distinct whiptail structure on the free end. The animal and vegetal poles are both cream in color, with eggs forming either a single or double row in each sac. The envelope of the egg sac is thicker than that of other congeners, but thinner than that of H. boulengeri, and of similar thickness to H. naevius, H. oyamai, and H. sematonotos. Hynobius oni has a small clutch size with a range of 16 - 36 eggs (Kanamori et al. 2022).
The larvae are most similar to those of H. hirosei, but have a smaller body size, longer axilla-groin distance, shorter tail length, shorter internarial distance, longer upper eyelid length, and larger medial tail width (Kanamori et al. 2022).
The dorsum is light brown with small, dark-brown dots and blotches in life. The venter is whitish and transparent and golden dots are scattered on the tail fin. In preservative, the dorsal coloration usually fades to a light brown and the golden dots fade to white (Kanamori et al. 2022).
Little is known about the larval life history of H. oni, however the density of overwintered larvae was found to be lower than that of H. hirosei (0.25 per square meter for H. oni and 10 per sq m for H. hirosei). Metamorphosis occurs in late July, and H. oni larvae might have a smaller metamorphosing size than H. hirosei. Hynobius oni were not observed in sympatry with other hynobiid salamanders (Kanamori et al. 2022).
Trends and Threats
Relation to Humans
Possible reasons for amphibian decline
General habitat alteration and loss
ETYMOLOGY: (Origin or explanation of scientific name)The species epithet, "oni", comes from “oni” in Japanese, which is a demon in Japanese folklore, because the type locality is on the Oni-ga-jo Mountains, where the castle of the oni is believed to have been (Kanamori et al. 2022). The Japanese name for H. oni is Nan-yo-sanshouo (Kanamori et al. 2022).
Kanamori S, Nishikawa K, Matsui M, Tanabe S. (2022). "A new species of lotic breeding salamander (Amphibia, Caudata, Hynobiidae) from Shikoku, Japan." PeerJ, 10, e13891. [link]
Originally submitted by: Madeline Ahn (2022-09-30)
Description by: Madeline Ahn (updated 2022-09-30)
Distribution by: Madeline Ahn (updated 2022-09-30)
Life history by: Madeline Ahn (updated 2022-09-30)
Larva by: Madeline Ahn (updated 2022-09-30)
Trends and threats by: Madeline Ahn (updated 2022-09-30)
Relation to humans by: Madeline Ahn (updated 2022-09-30)
Comments by: Madeline Ahn (updated 2022-09-30)
Edited by: Ann T. Chang (2022-09-30)
Species Account Citation: AmphibiaWeb 2022 Hynobius oni: Nanyo salamander <https://amphibiaweb.org/species/9564> University of California, Berkeley, CA, USA. Accessed Oct 2, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 2 Oct 2023.
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