Spotless Stout Newt

A moderate to large newt. The morphology and size are similar to (or larger than) P. brevipes. Females from Mt. Dayao (Guangxi Province, China), the type locality, can easily attain 190 mm in total length (with a snout-vent length of about 105 mm). Males are significantly smaller and weigh less than females (Xu et al. 2002). Tail is shorter than the snout-vent length. Head is flat, and the trunk is stout and robust. Snout is very broad in some populations, so the head is almost rectangular in shape. Eyes are small and are located at or anterior to the jaw angle. Labial folds are more conspicuous on the upper jaw than the lower jaw. Two lines of vomerine teeth orient in a ¦«-shaped manner, converging anteriorly. A gular fold is present and a parotoid region is evident. There is no vertebral ridge, but a vertebral groove may be present (Fei et al. 2006). The skin is very smooth with secretion of mucus. Limbs are relatively short. Animals of 190 mm long have forelimbs of only 20 mm. When the forelimb and hindlimb are pressed towards each other against the flank, the digits never meet. Digits are short and partially webbed. The lengths of fingers are 3 > 2 > 4 > 1, and the lengths of toes are 3 > 4 > 2 > 5 > 1. The anterior part of the tail is rounded, and the posterior part is laterally compressed like a paddle (leading to one common name of Paddle Tail Newt). Sexually matured males have papillae at the cloaca.Live animals are uniformly brown to dark brown on the dorsal side, and lack the black dots that characterize P. brevipes. Some P. labiatus develop two dorsolateral lines of red flecks. Orange blotches are present on the ventral side, which are well defined in juveniles, blurred in subadults, and finally washed out in aged animals. After preservation, the orange or red coloration turns to ivory white. No pattern difference is confirmed between males and females.Larvae are gray on the back and white on the ventral side (Zhao et al. 1994). Fully metamorphosed juveniles reach about 70 to 80 mm, and are sexually mature at 125 mm (Fei et al. 2006).According to current taxonomy, Pachytriton brevipes (Sauvage 1876) and Paramesotriton labiatus (Unterstein 1930) are mainly distinguished by their coloration (Fei et al. 2006). When Unterstein (1930) published P. labiatus (originally as Molge labiatum), he made little attempt to compare this species to P. brevipes in terms of color difference. Therefore, P. labiatus was stated to have no recorded characters different from P. brevipes (Pope 1931; Chang 1936). In Pope's (1931) description of Chinese amphibians from Fujian Province, he apparently had noticed the color distinction between P. brevipes and P. labiatus, yet he believed the coloration was not adequate for justifying separate species. Chang (1936) further discussed the color pattern of specimens from Zhejiang Province, but only as variations of P. brevipes. Hu et al. (1973) collected specimens from Guizhou Province, addressed the chromatic dissimilarity with P. brevipes, and recognized P. labiatus as a subspecies of P. brevipes. Not until Zhao and Hu (1984) confirmed the stability of color pattern and claimed no intermediate form in contact zones, was P. labiatus classified as a valid species.

According to current taxonomy (Zhao and Hu 1984; Fei et al. 2006), Paramesotriton labiatus has a wider altitudinal occurrence than P. brevipes. Pachytriton brevipes can be found in streams from 50 m to 1800 m (Fei et al. 2006). Two allopatric distributions occur in Southern China. One range includes Guizhou, Hunan, Guangxi and Guangdong Provinces, and the other one includes Anhui, Zhejiang and probably Jiangxi Provinces (Fei et al. 2006).

Paramesotriton labiatus inhabits mountain streams of various altitudes. Some streams are several meters wide and about one meter deep, whereas others are mere trickles of 20 to 40 cm deep. Water can be either clear or extremely dirty (due to flooding). The species is mostly aquatic. Populations in Hunan Province hibernate from November until April in crevices or under boulders where water is present (Zhao et al. 1994). The newts hide in shelters during daytime, and are active at night. The breeding season typically begins in April and lasts to July (Fei et al. 2006), but populations in Guangdong Province (southernmost distribution) may postpone to September and October (Xu et al. 2002). Under captivity, the species exhibit certain courtship behaviors (Sparreboom and Thiesmeier 1999). When a male senses the presence of a female, he swims toward her immediately and tries to block her path. Then the male positions itself perpendicular to the female's body, slowly fanning his tail tip near her snout. The female may either swim away or stay motionless if she is interested. After several bouts of tail-fanning, she moves towards the male, who turns around and begins to retreat. The female touches the male's tail while following. Finally, the male deposits a spermatophore and the female, creeping behind, picks it up with her cloaca. Females lay around 40 single eggs at the lower surface of the rocks in the streams, and sometimes the eggs congregate to form a patch (Zhao et al. 1994). However, more than 160 eggs can be found in the ovaries of gravid females (Xu et al. 2002). The ovum is milky white and attains 3 to 4 mm in diameter (Zhao et al. 1994). There are three jelly capsules enclosing the ovum, so the egg is about 10 mm in diameter (Zhao et al. 1994). The incubation period is around 2 months at the water temperature of 13~15 degrees C, and females vigorously protect the egg clutch (Thiesmeier and Hornberg 2003). Females do not leave the nesting site during this period and may eat dead eggs (Sparreboom and Thiesmeier 1999). Paramesotriton labiatus feeds on earthworms, other aquatic arthropods and insect larvae. The author observed two animals scrambling for the same earthworm from the two ends. After their snouts met, they rolled rapidly like feeding crocodiles. When captured, the animal may emanate a strong sulfurate odor (Fei et al. 2006). It may also emit food from the stomach. Zhao et al. (1994) recorded anti-predator postures including stretching limbs, lifting the head and tail, and exposing the orange ventral blotches.

The species is abundant in its range. Zhao et al. (1994) compared the number of animals collected in 1986 and 1993, and found no sign of population decline. However, large numbers of wild-caught animals appear in the pet trade every year. Local inhabitants may sell them as juvenile giant Chinese salamander (Andrias davidianus; Xu et al. 2002). Human exploitation and habitat destruction are the two most important factors affecting P. labiatus IUCN (2006).

Paramesotriton labiatus is a species of newt in the family Salamandridae. It is endemic to Guangxi, China. In literature prior to 2011, this species may have been confused with Paramesotriton chinensis, Pachytriton granulosus, or Paramesotriton ermizhaoi (the last now in synonymy). This species has several vernacular names, including Unterstein's newt, spotless stout newt, spotless smooth warty newt, Zhao Ermi's smooth warty newt, and paddletail newt.