Description
Onychodactylus pyrrhonotus is a slender-bodied salamander with a male snout-vent length range of 59.7 - 75.8 mm and female snout-vent length range of 58.0 - 79.4 mm. The head is generally ovular in shape, slightly depressed, andlonger than wide. The snout is short and rounded, jutting somewhat farther out than the lower jaw. The nostrils sit close to the snout. It has large eyes that protrude prominently from the head and has a gular fold posteroventral to the head. It also has a well-developed parotoid gland located at the posterior side of the head at level with the gular fold that is oval in shape and around 1.5 times longer than wide. The postorbital groove is also quite distinct. The skin is smooth and there are 12 - 18 costal grooves on the elongated and cylindrical trunk. The forelimbs are generally thin, with the lengths of the fingers measuring from I < II < IV < III. The hind limbs are generally a bit longer and more robust with toes measuring from I < V < II < III < IV. When the limbs are adpressed towards each other, the digits are separated by one coastal fold. The palms and planters have asperities and slight tubercles. The digits end in horny claws. The vent is presented as a swollen, longitudinal slit that is about 10.3% of the snout-vent length. One-third of the slit’s anterior edge forms a precloacal skin fold, which is as wide as two-fifths of its cloacal length. There are a series of black precloacal spines within the skin fold. It compresses laterally toward the tip forming a fin-like shape. The base of the cylindrical tail is also swollen. In both sexes, the tail is longer than the snout-vent length by about 130.8% (Yoshikawa and Matsui 2022).

DIAGNOSIS:

Onychodactylus pyrrhonotus is easily differentiated by its distinct and sharply defined scarlet, orange, pink, or yellow dorsal markings and purple venter with dusty white dots. More specifically, within the O. japonicus species complex, which typically have distinct dorsal markings, O. fuscum has a generally dark brown dorsum and no distinct markings and O. intermedius, O. nipponoborealis, and O. tsukabaensis have less defined dorsal markings that are often obscured, and color varies from yellow to ochre to brown to reddish-brown. Coloration among populations of O. japonicus is highly variable, but O. pyrrhonotus can still be differentiated by color: northern Kinki District and eastward populations of O. japonicus have generally obscured and only sometimes sharply defined dorsal markings that vary in color (yellow, ochre, brown, orange), and fewer white spots on the venter than O. pyrrhonotus. Chugoku mountains populations of western Honshu (allopatric with O. pyrrhonotus) have similar red to reddish brown dorsal color, but also have pair of dark markings on chest, and fewer white spots on venter. Kii Peninsula populations of southern Kink District and Mie Prefecture (sympatric with O. pyrrhonotus) are very similar in color to O. pyrrhonotus by having light-orange to pink dorsal markings on black background, but can typically be differentiated from O. pyrrhonotus by having a pair of dark markings on chest and ventral white spots are typically absent or scarce. Its sister species, O. kinneburi, has sharply defined yellow to orange dorsal markings, and no white dots or spots on venter. Lastly, O. pyrrhonotus is distinguishable from O. fischeri, O. koreanus, O. zhangyapingi, and O. zhaoermii as the three others species have indistinct markings or scattered yellow spots on dorsum (Yoshikawa and Matsui 2022).

Onychodactylus pyrrhonotus is also differentiated by morphological characters. Specifically, O. pyrrhonotus and O. kinneburi are most similar, but O. pyrrhonotus has a smaller body, fewer presacral vertebrate, and wider internarial distance relative to head width. Onychodactylus fischeri has a larger number of costal grooves and presacral vertebrae. Onychodactylus nipponoborealis generally has a larger snout-vent length and more costal grooves, and females have smaller relative (to their snout-vent length) head widths, chest width, and snout lengths while males have larger ratios of snout-vent to axilla-groin length. Onychodactylus tsukabaensis has a larger ratio of snout-vent to tail length, snout-vent to axilla-groin length, internarial distance to head width, and interorbital distance to head width, along with more costal grooves. Female O. tsukabansis have smaller head widths, chest widths, and snout lengths relative to their snout-vent length than O. pyrrhonotus, while male O. tsukabansis have a larger snout-vent to tail length ratio and a larger interorbital distant to head width ratio than O. pyrrhonotus. Lastly, O. japonicus has fewer costal grooves, and in males, a larger snout-vent to forelimb length ratio while in females the snout-vent length to chest ratio is smaller. In populations of O. japonicus that are sympatric with O. pyrrhonotus, the former has larger males (Yoshikawa and Matsui 2022).

COLORATION:

In life, the dorsum is purplish-black with a distinct scarlet, orange, pink, or rarely yellow dorsal stripe from head to tip of tail. The dorsal stripe is sharply defined and wavy. The tail section of the dorsal stripe narrows toward the tip. The dorsal surface of the limbs have sparse scarlet flecks. The sides of the body are purplish dark gray with sparse scarlet flecks and/or fine white dots that gradually fade toward the ventrum. The ventrum is purplish gray with fine white dots. The golden upper iris is slightly mottled with brown while the lower iris is dark-brown. When preserved in alcohol, color and pattern generally fade, with immediate bleaching to dorsal stripe (Yoshikawa and Matsui 2022).

VARIATION:

Onychodactylus pyrrhonotus exhibits sexual dimorphism. Females are larger than males but, relative to snout-vent length, males have significantly larger tail lengths, larger basal tail height, larger basal tail widths, larger medial tail heights, and smaller axilla-groin distances. Males also have more robust and thicker hind limbs than females. Adult specimens collected during the breeding season had swollen paratoid glands. Males also develop black tubercles and asperities on the palms and soles. Females only develop them on the soles. The breeding males also have dermal flaps around the posterior edge of the hind limb. Females have an inverse narrow U-shared precloacal skin fold while males have an inverted V-shaped skin fold. Additionally, color patterns and color vary among live individuals. The dorsal stripe can be straight, uneven, or broken into a series of blotches or spots, which can then range in color from scarlet to light orange to pink and rarely yellow. Southern populations tend to have a larger snout-vent length and a paler dorsal coloration than northern populations (Yoshikawa and Matsui 2022).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

View distribution map in BerkeleyMapper.

Onychodatctylus pyrrhonotus has a fairly limited distribution. It’s known throughout the central Honshu region of Japan and is found in the Gifu, Ishikawa, and Fukui Prefectures of the Chūbu region, and the Kyoto, Mie, Nara, and Shiga Prefectures of the Kansai region. The species probably occurs in Wakayama Prefecture in the southern Kii Peninsula as well. They live on the forest floor, near cool and humid streams in montane forests about 1,000 meters above sea level (Yoshikawa and Matsui 2022).

Life History, Abundance, Activity, and Special Behaviors
Non-breeding adult life history is not well known. However, juveniles and adults are mainly terrestrial and live in cool, humid forest floors in the mountains (Yoshikawa and Matsui 2022).

The breeding season is in the early summer (late May to early July). Breeding sites are underground in the flowing water near headstreams (Yoshikawa and Matsui 2022). The reproductive type is currently unknown for a majority of the species in the Onychodactylus genus. However, there has been one observed instance of external fertilization in O. koreanus, so it could be hypothesized that others in the genus are also external fertilizers (Poyarkov et al. 2012).

At the time of the species description, only one pair of unfertilized egg sacs were obtained. They were found strongly adhered without gelatinous stalks to stone. The egg sacs are covered by a layer of strong, but elastic translucent gelatin, which provides some extra protection for the eggs. They were long and narrow, and had very weak, longitudinal grooves on the surface. The pigmentless, yellowish-white eggs were arranged in two rows at the basal half of sac and single row at the tip of the sac, with a clutch size of 30 (15 eggs per sac) and egg diameters that ranged from 3.7 - 5.5 mm (Yoshikawa and Matsui 2022).

Larval metamorphosis season and size are unknown, but a juvenile that probably metamorphosed about 7 months before had an snout-vent length of 36.1 mm (Yoshikawa and Matsui 2022).

Juveniles are often found on the forest floor near streams (Yoshikawa and Matsui 2022).

Onychodactylus pyrrhonotus is sympatric with O. japonicus on Mt. Horai and Mt. Bunagatake in Otsu-shi, Shiga Prefecture, and breeding individuals, hatchlings, and larvae of both species have been observed co-occurring which suggests they breed in the same place in the same season, but reproductive isolation is evident (Yoshikawa and Matsui 2022).

Predation by a snake Rhabdophis tigrinus has been observed (Yoshikawa and Matsui 2022).

Larva

Larval Morphology:

Larvae of the fireback clawed salamander have a snout-vent length of 16.6 - 43.2 mm and a tail length of 13.7 - 42.6 mm. This adds up to an overall total length of 30.6 - 85.8 mm. The head of the larvae is rectangular and blunt in nature, with three pairs of short external gills. At the posterior half of the upper jaw, it has a well-developed labial fold. The caudal fin sits lower, while the dorsal fin, which originates from the level of the hind limb to the cloaca, sits relatively higher than the ventral fin. In comparison, the ventral fin grows from the posterior four-fifths to two-thirds of the tail. The tail tip is rounded, the skin folding on the posterior edge. Like the adults, its digits have small, curved, black claws but have dark asperities on both the surfaces of the palm and sole (Yoshikawa and Matsui 2022).

Larval Coloration:

Larvae are usually a uniform dark brown with light stripes or blotches or a yellowish gray with indistinct markings. Around their third year, still in their premetamorphic stage, they often have blotches or a stripe similar to what is observed in adults. This stripe is usually scarlet to light orange on a black or purplish-black background. Their claws and asperites are black (Yoshikawa and Matsui 2022).

Larvae inhabit open streams and may metamorphose after two or more years, as in similar species (Yoshikawa and Matsui 2022).

Observed diets from Horai, Otsu-shi, Shiga Prefectures were nymphs, mayfly, and other small aquatic insects or invertebrates (Yoshikawa and Matsui 2022).

Trends and Threats
This species is not abundant, and its habitat appears to be discontinuous and fragmented in its known distribution of approximately 10,000 square kilometers. Prior to its description, O. pyrrhonotus was considered part of O. japonicus, which is “Critically Endangered” on the Red List of Kyoto Prefecture, “Vulnerable” on the Red Lists of Mie and Nara Prefectures, “Near Threatened” on the Red List of Shiga Prefecture, and not listed in the Red Lists of Fukui, Gifu, and Ishikawa Prefectures. Based on the criteria used in Japanese and IUCN Red Lists, Yoshikawa and Matsui propose that this species be designated as “Vulnerable” in those red lists (Yoshikawa and Matsui 2022).

Comments

PHYLOGENETIC RELATIONSHIPS:

Maximum Likelihood analysis on cyt b found that O. pyrrhonotus, referred to as the Onychodactylus sp. Kinki group in the species description, is sister to O. kinneburi (Yoshikawa and Matsui 2022).

Onychodactylus pyrrhonotus is thought to have diverged from O. kinneburi about 2.5 million years ago, due to the formation of Kii Strait, which separated the Kii Peninsula and Shikoku. Several species of salamander in the surrounding area, such as Hynobius guttatus and H. tsurugiensis, show similar phylogenetic relationships, which may suggest that the Kii Strait plays an important role in the differentiation of the species (Yoshikawa and Matsui 2022).

ETYMOLOGY:

With its bright scarlet dorsum, the species epithet is derived from the Greek words “pyrrho-” and “-notus”, translating to “fire-colored” and “back,” respectively. The name was also inspired by the venter coloration of the Japanese fire-bellied newt, Cynops pyrrhogaster (Yoshikawa and Matsui 2022).

References
Poyarkov, N.A., Che, J., Min, M.-S., Kuro-O, M., Yan, F., Li, C., Iizuka, K., Vieites, D. R. (2012). Review of the systematics, morphology and distribution of Asian Clawed Salamanders, genus Onychodactylus (Amphibia, Caudata: Hynobiidae), with the description of four new species. Zootaxa, 3465(1), 1–106 . [link]

Yoshikawa, N., Matsui, M. (2022). A New Salamander of the Genus Onychodactylus from Central Honshu, Japan (Amphibia, Caudata, Hynobiidae). Current Herpetology, 41(1), 82–100. [link]

Species Account Citation: AmphibiaWeb 2023 Onychodactylus pyrrhonotus: Fireback clawed salamander <https://amphibiaweb.org/species/9522> University of California, Berkeley, CA, USA. Accessed Apr 27, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 27 Apr 2024.

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