Description

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.