Occidozyga obscura (Gray, 1831) Lyu & Wang & Zeng & Luo & Zhang & Guo & Ren & Qi & Mo & Wang, 2022

Lyu, Zhi-Tong, Wang, Jian, Zeng, Zhao-Chi, Luo, Lin, Zhang, Yan-Wu, Guo, Chun-Peng, Ren, Jin-Long, Qi, Shuo, Mo, Yun-Ming & Wang, Ying-Yong, 2022, Taxonomic clarifications on the floating frogs (Anura: Dicroglossidae: Occidozyga sensu lato) in southeastern China, Vertebrate Zoology 72, pp. 495-512 : 495

Occidozyga obscura (Gray, 1831) comb. nov.

Houlema obscura Gray 1831

Oxyglossa lima var. chinens Müller 1878

Oxydozyga lima - Stejneger 1925

Osteosternum amoyense Wu 1929

Ooeidozyga lima - Pope 1931; Smith 1931; Liu & Hu 1961

Occidozyga lima - Dubois 1981; Fei et al. 1990, 2009, 2010, 2012; Zhao & Adler 1993; Li et al. 2011; Mo et al. 2014.

Type materials.

Holotype. BMNH 1932.5.1.2, adult female, collected from China (discussion for the exact locality see Remarks below).

Specimens examined.

Seven adult males and three adult females. Males CIB 44475 -44476, from Guangzhou , Guangdong Province, China ; male SYS a000534, from Mt Danxia (25.0347 N, 113.7407 E), Renhua County, Guangdong; males SYS a008120-8121, 8123, 8125, and females SYS a008122, 8124, from Shimentai Nature Reserve (24.3818 N, 113.3927 E), Yingde City , Guangdong; female SYS a000488, from Mt Luoyang , Lingshan County , Guangxi Zhuang Autonomous Region, China .

Etymology.

The specific name obscura means ‘obscure’ in Latin.

Common name.

"Chinese floating frog" in English / "中国浮蛙 (zhōng guó fú wā)” in Chinese.

Diagnosis.

(1) Body stocky, size small, SVL 24.2-27.5 mm in adult males (n=7) and 31.5-32.2 mm in adult females (n=3); (2) snout short triangular shaped; (3) nostrils located dorsally; (4) eye orientation vertically; (5) loreal region oblique, not concave or convex; (6) interorbital space narrower than internarial distance; (7) tongue narrow and slender, unnotched, pointed distally, lingual papilla absent; (8) vomerine ridge and vomerine teeth absent; (9) supratympanic fold distinct, raised, and granulated, curved on the temporal region; (10) tympanum hidden, edge invisible; (11) fingers with rudimentary webs, toes with full webs; (12) heels not meeting, tibio-tarsal articulation reaching between the posterior and anterior of the eye.

Comparisons.

Occidozyga obscura comb. nov. was previously synonymized with O. lima . These two species are most similar to each other. However, Occidozyga obscura comb. nov. can be distinguished by the combination of the following characteristics: loreal region oblique, not concave or convex (vs. slightly concave in O. lima ), interorbital space narrower than internarial distance (vs. subequal), supratympanic fold distinct, raised, and granulated (vs. indistinct), inner metatarsal tubercle large and raised (vs. weakly projecting), and tibio-tarsal articulation reaching between the posterior and anterior of the eye (vs. reaching tip of nostril).

Occidozyga obscura comb. nov. furthers differs from O. berbeza by the supratympanic fold curved on the temporal region (vs. straight), fingers with rudimentary webs (vs. unwebbed), and outer metatarsal tubercle present (vs. absent). O. obscura comb. nov. distinctly differs from O. rhacoda by the dorsolateral fold absent (vs. present), and fingers with rudimentary webs (vs. unwebbed).

Occidozyga obscura comb. nov. can be easily distinguished from the remaining 13 congeners O. baluensis , O. celebensis , O. diminutiva , O. floresiana , O. laevis , O. magnapustulosa , O. martensii , O. myanhessei comb. nov., O. semipalmata , O. sumatrana , O. shiwandashanensis , O. swanbornorum comb. nov., and O. tompotika , by the tongue narrow and slender (vs. wide and swollen in all of these 13 species).

Re-description.

Based on the examined specimens (n=10). All specimens were similar in morphology. The measurements are given in Table 3 .

Body stocky, small-sized, SVL 24.2-27.5 mm (n=7) in males and 31.5-32.2 mm (n=3) in females. Head flat above, almost as wide as long (HDW/HDL 0.97-1.09, n=10); pineal ocellus absent; snout short triangular shaped, distinctly protruding beyond lower jaw, tip of snout rounded in dorsal view and profile; canthus rostralis absent, loreal region oblique, not concave or convex; nostril rounded, located dorsally, distinctly raised, closer to the tip of snout than to the eye; eye orientation vertically, pupil diamond shaped; interorbital space narrower than internarial distance; tympanum hidden, edge invisible; vomerine ridge and teeth absent; tongue narrow and slender, unnotched, pointed distally, lingual papilla absent.

Forelimbs short, lower arm 13-18% (n=10) of SVL and hand 26-32% (n=10) of SVL; fingers distinctly thin and long, relative finger lengths I<II<IV<III; tips of fingers pointed, not dilated, and without disks; distinct lateral fringes on inner and outer sides of each finger, fingers with rudimentary webs, more distinct between fingers I and II; subarticular tubercles present at the bases of each finger, prominent and rounded; supernumerary tubercles absent; inner and outer palmar tubercles prominent and rounded.

Hind limbs robust, tibia 41-47% (n=8) of SVL and foot 66-80% (n=8) of SVL; heels not meeting when hind limbs flexed at right angles to the axis of the body; tibio-tarsal articulation reaching between the posterior and anterior of the eye when hind limb is stretched along the side of the body; toes distinctly long and thin, relative lengths I<II<III<V<IV; tips of toes pointed, dilated into pear-shaped disks; toes with full webs, metatarsal web present, distinct lateral fringes on lateral edges of toes I and V; subarticular tubercles rounded, prominent; inner metatarsal tubercle large and long-elliptic, slightly raised, length twice the width; outer metatarsal tubercle relatively smaller than the inner metatarsal tubercle, distinctly raised and pointed, length slightly larger than width; inner tarsal fold relatively flat, in contact with the inner metatarsal tubercle; tarsal tubercle large and distinctly raised, close to the tibio-tarsal articulation.

Dorsal surface relatively rough, transverse wrinkles and dense tubercles on the dorsum, head, flanks, and limbs; small granules on the dorsal rears of hands and tarsi; not bearing spinules on the dorsal skin; supratympanic fold distinct, raised and granulated, extending from the posterior corner of the eye, curved on the temporal region, to the previous shoulder; dorsolateral fold absent. Ventral surface with large flattened tubercles, denser on the throat and thighs; dense granules on the ventral feet and tarsi.

Coloration.

In life (Fig. 3 ), dorsal surfaces vary from olive brown to dark brown; dorsum and flanks interspersed with irregular black speckles; mid-dorsal stripe grass-green with distinct border; lateral line system grayish brown to yellowish brown. Pupil bordered with yellow, iris beige to brown. Supratympanic fold olive-brown to dark brown. Skin of throat, chest, and belly uniform creamy white; gular with a pair of distinct or indistinct longitudinal dark stripes; skin of limbs dark gray, tubercles on ventral thighs and tibias creamy white.

In preservative (Fig. 4A, B ), dorsum light gray; black speckles on dorsal surface light brown; mid-dorsal stripe fainted and the border indistinct; ventral skin grayish white; tubercles on ventral surface more distinct.

Male secondary sexual characteristics.

Male with a single subgular vocal sac; in breeding season, a single, light grey nuptial pad on the dorsal surface of finger I, nuptial spinules invisible. Males (SVL 24.2-27.5 mm) distinctly smaller than females (SVL 31.5-32.2 mm) (Fig. 4A, B ).

Ecology.

This frog inhabits natural or artificial ponds and paddy fields in plain areas. They quickly dive underwater after being disturbed during the daytime, while become relatively insensitive at night. Males call in the water surface or waterside grass from dusk to dawn, more active during the rain. The breeding season is from April to August (this study; Fei et al. 2009).

Distribution.

Occidozyga obscura comb. nov. can be recognized from several localities of Guangdong and Guangxi, southeastern China (Figs 1 , 2 ), based on the analyzed vouchers in this work. The previous records of O. lima from Guangdong, Guangxi, Hong Kong, Macao, and Fujian, southeastern China are reassigned to O. obscura currently (see Remarks below). The records of O. lima from Yunnan require further clarifications with molecular and morphological vouchers (which might be close to the lineage of O. cf. lima based on the biogeographical similarity).

Conservation status.

This species was previously reported as common and widespread species in southeastern China under the nomen O. lima , but its population quantity is found rapidly declining due to the influence of human activities such as pesticide abuse and urban construction. The populations in Hong Kong, Macao, Shenzhen, Guangzhou, and Xiamen might disappear, as no more reports and vouchers in nearly 20 years (this study; Chan 2013). We recommend Occidozyga obscura comb. nov. to be listed as Endangered (EN) [IUCN Red List criteria A2cd].

Remarks.

The type specimen of Occidozyga obscura comb. nov. was collected by John Reeves (1774-1856) but the exact type locality was not given in the original description ( Gray 1831). Zhao & Adler (1993) speculated that the type specimens may be from somewhere in southeastern China, especially Macao or Canton (= Guangzhou) in Pearl River Delta, where John Reeves lived and worked in.

Moreover, there were two historic species currently regarded as synonymies of O. lima , namely Oxyglossa lima var. chinens and Osteosternum amoyense ( Stejneger 1925; Smith 1931; Pope 1931). The type locality for Oxyglossa lima var. chinens is Lilong, Canton (= Lilang, Shenzhen, Guangdong), and for Osteosternum amoyense is Amoy (= Xiamen, Fujian). During our field surveys, we are unable to observe any frogs that resembled these two historic species from Shenzhen or Xiamen, possibly due to the dramatic urbanization of these two cities. Nevertheless, according to their original descriptions and distributions, we propose to transfer these two taxa to be the synonymy of Occidozyga obscura comb. nov.

Figures

Figure 1. Phylogenetic trees of the genus Occidozyga sensu lato based on mitochondrial genes 16 S and CO 1. Bayesian posterior probabilities (BPP) and bootstrap supports (BS) are labeled above and below the nodes respectively. Numbers at the terminal of the lineages correspond to the IDs in Table 1.

Figure 2. Map showing the floating frogs Occidozyga obscura comb. nov., Occidozyga lingnanica sp. nov., and their closest congeners. Numbers correspond to the IDs in Table 1.

Figure 3. Morphological features of Occidozyga obscura comb. nov. in life. A - D dorsolateral view, ventral view, left hand, and right foot of SYS a 008122 E dorsolateral view of SYS a 008123 F dorsolateral view of an uncaptured individual in situ from Shimentai Nature Reserve.

Figure 4. Morphological features of Occidozyga obscura comb. nov. and Occidozyga lingnanica sp. nov. in preservative. Occidozyga obscura comb. nov.: A adult male SYS a 008121 B adult female SYS a 008122; Occidozyga lingnanica sp. nov.: C adult male paratype SYS a 007373 D adult female paratype SYS a 007375. 1 dorsal view 2 ventral view.