Description
Adults are 48-87 mm snout-vent length and 88-155 mm total length. The trunk is long and robust, the tail thick and often vertically compressed. There are 13, occasionally 14, costal grooves. The limbs are thick-set and very short. There is a space of 1.5-4.5 costal groves between the fore and hind toes when the limbs are adpressed to the flank. The hind feet have 5 toes. The ground color is blackish brown, possibly with a purplish tinge. The dorsal and lateral surfaces are blotched silvery or whitish. The size of the blotches is irregular, though small on the head and back and much larger on the flanks and tail. The ventral surface is lighter. Because this species is widely distributed there is considerable color variation. The blotches in some populations may be yellowish and almost completely absent in others (Goris 2004).

This species occurs in sympatry with Hynobius kimurae in Honshu and with H. stejnegeri in Kyushu.

H. kimurae can usually be distinguished by the yellowish or golden color and uniform size of its blotches and H. stejnegeri by its larger size and generally large amber-colored blotches on both flanks and back (Goris 2004).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (2 records).

This species inhabits mountainous regions throughout Kyushu and Shikoku, and from central to western Honshu. This species also frequents deciduous, coniferous, and mixed forests on mountain slopes, hiding under logs and rocks or forest litter, and foraging at night and on rainy days. It presumably eats the same prey items as H. kimurae, but neither species seems to displace the other. There is no hint of what ecological mechanism renders this possible (Goris 2004).

Life History, Abundance, Activity, and Special Behaviors
This species breeds in mountain brooks. Like H. kimurae, it lays its egg sacs under rocks in the headwaters or side rivulets of mountain brooks, usually in eddies where the current is not too strong. Unlike H. kimurae, it does not migrate to the breeding sites until the spring thaw, so that breeding occurs from the end of March to the end of May. Therefore, where both species breed in the same brook, H. naevius larvae may be preyed upon by the larger, older H. kimurae larvae (Goris 2004).

A pair of elongate and spiral egg sacs, each containing a total of 17-36 eggs, is laid at a time. The gelatinous envelope of the sacs is transparent and tough but less so than that of H. kimurae egg sacs (Goris 2004).

The egg is white in color, with much yolk, and has a diameter of about 5 mm (Junji Oyama 1929).
Gastrulation is completed a week after spawning. Soon after this, neural folds are formed. About ten days are required for the completion of the neural grove. After two weeks the fusion of the neural folds takes place and the head part is distinguishable. The head becomes more well-defined two or three days after this. The rudiments of the external gills arise behind the eyeballs and the tail appears on the hinder part of the body. At this time the embryo is 8 mm in length, a little bent, and holds a round yolk mass on the ventral region. Three weeks after spawning, the embryo becomes straight and 15 mm in total length, the head being about 2 mm, the tail about 5 mm. The external gills consist of three pairs of rods and are 1 mm in length. The fore-limbs now project and the nostrils appear. Black pigment appears in the eyes. The fin arises on the tail. The yolk mass becomes elongated, lying along the body. Two or three days later the external gills increase in length and little branches spring up from them. The rudiments of the hind-limbs become visible. Pigment gradually appears over the surface of the body. By the end of the fourth week the total length reaches 19 mm, external gills measure 5 mm, and two or three toes appear on the fore-limbs. The embryo hatches out in the fifth week. At this time the total length is 21-22 mm, the fore-limbs measure 2 mm, and the hind-limbs 1 mm. A good quantity of yolk remains in the abdomen. Newly hatched larvae have no balancers and generally lie on their side on the bottom of the water, remaining in this position until the fore-limbs are strong enough to perform their function (Junji Oyama 1929).

The larvae live along the edges of the stream where the current is weak and feed on aquatic insects and other prey like H. kimurae. The larvae of some populations have claws, which disappear at metamorphosis. Some larvae metamorphose and leave the water from the middle of August to the end of September, while others remain in the water until the following spring or summer (Goris 2004).

Comments
The name "spotted salamander" has also been used (Goris 2004).

References

Goris, R.C. and Maeda, N. (2004). Guide to the Amphibians and Reptiles of Japan. Krieger Publishing Company, Malabar, Florida.

Oyama, J. (1929). ''Some embryological notes of Hynobius naevius.'' Copeia, 1929, 92-94.

Species Account Citation: AmphibiaWeb 2008 Hynobius naevius: Blotched Salamander <https://amphibiaweb.org/species/3889> University of California, Berkeley, CA, USA. Accessed Nov 12, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 12 Nov 2024.

AmphibiaWeb's policy on data use.