Description
Hynobius tosashimizuensis is a relatively large species of salamander with a mean snout-vent length range of 60.0 to 72.7 mm in males and 65.0 to 69.0 mm in females. The skin is smooth and shiny. The head is slightly longer than it is wide, and the snout is rounded. Their vomerine teeth are U-shaped and gular folds are present. There are 10 costal grooves on their cylindrical bodies. Specimens have four fingers on each of their forelimbs and five fingers on each hindlimb with no webbing of digits. When the limbs are adpressed, they overlap by two costal folds. They have a Y-shaped cloaca and a tail that is laterally compressed toward the tip (Sugawara et al. 2018).

The fingers and toes of larval H. tosashimizuensis lack claws. One pair of balancers – ectodermal projections from the head – are visible during early developmental stages (Sugawara et al. 2018).

The most significant diagnostic characteristic used to distinguish H. tosashimizuensis from H. dunni is the presence or absence of black spots on their dorsum; Hynobius dunni has these spots while H. tosashimizuensis does not. Hynobius tosashimizuensis also has a shorter mean snout-vent length. Subsequently, H. tosashimizuensis also have significantly shorter measurements than H. dunni in the following average lengths: head length, tail length, trunk length, axilla-groin distance, forelimb length, hindlimb length, median tail width, and upper eyelid length. Lastly, the egg sacs of H. tosashimizuensis are coil-shaped and the egg sacs of H. dunni are crescent-shaped (Sugawara et al. 2018).

Hynobius tosashimizuensis can be distinguished from H. nebulosus as their distributions do not overlap and H. nebulosus specimens have a bright yellow stripe on the ventral edges of their tails. Hynobius nebulosus also has V-shaped vomerine teeth, whereas H. tosashimizuensis has U-shaped vomerine teeth (Sugawara et al. 2018).

In life, H. tosashimizuensis has a uniformly dark green or dark brown dorsum with no distinct black spots. The venter is slightly lighter and covered in white spots. White spots can also be found extending from the lateral side of the head all the way to the tail. They have dark brown irises. Preserved specimens will typically turn dark gray (Sugawara et al. 2018).

Larval H. tosashimizuensis have black dots on the lateral surface of their tail (Sugawara et al. 2018).

Variation among H. tosashimizuensis specimens is minimal. While most individuals do not have black spots on their dorsum, some H. tosashimizuensis specimens have indistinct black dots on their dorsal surface. Males are generally larger than females (Sugawara et al. 2018).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

View distribution map in BerkeleyMapper.

Hynobius tosashimizuensis is endemic to the southwest region of Shikoku Island in southwest Japan. It is one of only two species of Hynobiidae found on Shikoku Island, the other species being H. nebulosus. Hynobius tosashimizuensis is only found within an extremely limited distribution area of approximately 0.35 km² located near Tosashimizu City, Kochi Prefecture, Shikoku, Japan. This locality is approximately 350 m above sea level, and the most dominant vegetation type is Japanese cedar. It’s believed that this species is unlikely to be distributed outside of this locality because the surrounding environment is unsuitable for the life and breeding of H. tosashimizuensis (Sugawara et al. 2018).

Life History, Abundance, Activity, and Special Behaviors
Hynobius tosashimizuensis appears to be a relatively standard pond breeding salamander (Sugawara et al. 2018).

Their breeding season runs from January to April. Their egg sacs are coil shaped. Hynobius tosashimizuensis attaches its egg sacs to fallen branches in still ponds found at the edge of forests (Sugawara et al. 2018).

Larvae have a pair of balancers during their early development stages that they subsequently lose (Sugawara et al. 2018).

Calls and reproductive behavior have not yet been witnessed or recorded (Sugawara et al. 2018).

Trends and Threats
While H. tosashimizuensis is not under any immediate threat due to encroaching habitat loss or other human action, its small geographical distribution makes it vulnerable to extinction. The area surrounding its habitat is inhabitable by the species; their population cannot grow beyond what their current area of distribution can support. Little is known about their historical population trends as they were not previously surveyed (Sugawara et al. 2018).

The species H. dunni and H. tosashimizuensis were both declared a Natural Monument of Tosashimizu City in April of 2017 under the assumption that they were both H. dunni. Local landowners have reportedly been protecting the species within the Tosashimizu city region for some time, despite the lack of habitat protection from any official local or national governments. Hynobius tosashimizuensis is not regularly consumed as food or collected for the pet trade. However, the ease of collecting specimens could potentially make them vulnerable in the future (Sugawara et al. 2018).

Relation to Humans
Local landowners have reportedly been protecting the species within the Tosashimizu city region for some time, despite the lack of habitat protection from any official local or national governments. Hynobius tosashimizuensis is not regularly consumed as food or collected for the pet trade (Sugawara et al. 2018).

Possible reasons for amphibian decline

General habitat alteration and loss
Subtle changes to necessary specialized habitat
Habitat fragmentation
Loss of genetic diversity from small population phenomena
Loss of distinctiveness through hybridization

Comments

It was previously thought that there were three geographically distinct populations of the same species, H. dunni, found in three different locations. These populations were given the following names based on their geographical distributions: Oita, Miyazaki, and Tosashimizu. Maximum Likelihood and Bayesian Inference methods to reconstruct the phylogenetic tree from 16S and cytochrome b genes showed that all H. dunni specimens formed a monophyletic group that was separated from all H. tosashimizuensis specimens. Furthermore, morphological analysis supported the elevation of H. tosashimizuensis as a species from H. dunni as they differ in 13 morphological characters. Hynobius tosashimizuensis also differs from the Miyazaki population in seven morphological characters. These analyses confirmed that the population found at Tosashimizu is a new species. The closest relative of H. tosashimizuensis is H. nebulosus (Sugawara et al. 2018).

The scientific name for H. tosashimizuensis is derived from the city where the species occurs: “Tosashimizu City” located within the Kochi Prefecture (Sugawara et al. 2018).

References

Sugawara, H., Watabe, T., Yoshikawa, T., Nagano, M. (2018). "Morphological and molecular analyses of Hynobius dunni reveal a new species from Shikoku, Japan." Herpetologica, 74(2), 159-168.

Species Account Citation: AmphibiaWeb 2021 Hynobius tosashimizuensis: Tosashimizu-sanshouo <https://amphibiaweb.org/species/8847> 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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