Platysmacheilus Lo, Yao & Chen, 1977

Sun, Zhi-Xian, Tang, Wen-Qiao & Zhao, Ya-Hui, 2025, Generic revision on the Biwia – Microphysogobio complex (Cypriniformes, Gobionidae) with descriptions of three new genera, Zoosystematics and Evolution 101 (4), pp. 2013-2037 : 2013-2037

Platysmacheilus Lo, Yao & Chen, 1977

Fig. 10

Platysmacheilus Lo, Yao & Chen, 1977: 533 . Type species: Saurogobio exiguus Lin, 1932 .

Diagnosis.

This genus can be distinguished from the other genera within the Pseudogobionini by the combination of the characters: (1) mouth horseshoe-shaped and inferior; (2) central portion of the anterior papillae small and usually equal-sized, in tight contact with each other, several rows; (3) lower lip without anterior fold; (4) lobes on lower lip formed together, with a notch anteriorly, and free posteriorly; (5) upper jaw narrow, the horny margin width less than half mouth width; (6) barbel in one pair; (7) pharyngeal teeth in one row; (8) anterior chamber of the air bladder enclosed in fibrous capsule; (9) posterior chamber relatively small, length smaller than half eye diameter, thin.

Description.

Body elongated, abdomen rounded; caudal peduncle short, compressed laterally. Mouth horseshoe-shaped and inferior; barbel one pair; lips thick, with developed papillae; central portion of the anterior papillae small and usually equal-sized, in tight contact with each other, several rows; lateral portion of anterior papillae in several rows; lower lip without anterior fold; lobes on lower lip formed together, with a notch anteriorly, and free posteriorly. Jaws with horny sheathed edge; upper jaw narrow, horny margin width less than half mouth width (Fig. 3 F ). Body covered with moderately large cycloid scales. Thoracic region scaleless, mid-ventral region covered with scales. Anus positioned in the anterior one-third of pelvic-fin insertion and anal-fin base. Lateral line complete, almost straight. Lateral-line scales usually 37–39; scales above lateral line 4.5; scales below lateral line usually 2.5; predorsal scales 8–11; circumpeduncular scales 12. Distal margin of expanded dorsal fin steep sloped, usually slightly concave, with three unbranched and seven branched rays, pectoral fin with one unbranched and 11–14 branched rays, pelvic fin usually with one unbranched and seven branched rays, anal fin with three unbranched and six branched rays; caudal fin forked, with one simple ray and nine branched rays on upper lobe and eight branched rays and one simple ray on lower lobe, lobes pointed. Pharyngeal teeth in one row. Air bladder relatively small, possessing two chambers; anterior chamber rounded, enclosed in a thick fibrous capsule; posterior chamber small, length less than half eye diameter, smaller than anterior chamber length, thin. Intestine relatively long.

Distribution.

This genus is distributed in southern China, including the middle portions of the Yangtze River Basin and northern tributaries of the Xijiang River (which belongs to the Pearl River Basin). This genus is endemic to China (Fig. 5 E ).

Etymology.

The word “ platysma- ” derived from the Greek word “ platysma ”, meaning flat object; “ - cheilus ” derived from the Greek word “ cheilos ”, meaning lip. It means having a flat lower lip. The generic name in Chinese is “ 片唇鮈 ” 属, and the Chinese Pinyin name is “ Piàn Chún Jū ” Shǔ.

Species included.

Platysmacheilus exiguus (Lin, 1932) (type species).

Platysmacheilus longibarbatus Lo, Yao & Chen, 1977 .

Remarks.

This study places two valid species in this genus, the type species Platysmacheilus exiguus and P. longibarbatus . Platysmacheilus nudiventris Lo, Yao & Chen, 1977 , P. obtusirostris (Wu & Wang, 1931) , and P. wangcangensis Chen, Yang & Guo, 2020 do not belong to this genus because they have significant morphological differences from the type species (e. g., the central portion of the anterior papillae in these three species is in one row; the lower lip is trilobed in P. nudiventris and P. obtusirostris ). This study treats P. nudiventris as a Microphysogobio species based on its wide upper jaw horny margin and small posterior chamber of the air bladder. Platysmacheilus obtusirostris and P. wangcangensis , possessing a narrow horny margin on the upper jaw, a loosely arranged central portion of the anterior papillae, and an exposed lower jaw, should be placed in Oriengobio gen. nov. Platysmacheilus zhenjiangensis Ni, Chen & Zhou, 2005 , collected from the lower Yangtze River in Zhenjiang City, Jiangsu Province, also does not belong to Platysmacheilus . It should be a junior synonym of Oriengobio microstomus (Yue, 1995) , comb. nov.

Figures

Figure 3. Lip papillae patterns of the type species of seven genera within the Biwia – Microphysogobio complex, with a diagrammatic illustration showing the structures. A. Biwia zezera, KUN-P 040282; B. Microphysogobio hsinglungshanensis, ASIZB 240788; C. Huigobio chenhsienensis, SHOU 20231209015; D. Oriengobio fukiensis, ASIZB 220659; E. Mesophysogobio kachekensis, ASIZB 69768; F. Platysmacheilus exiguus, ASIZB 220879; G. Crossocheilogobio tafangensis, ASIZB 60212; H. diagrammatic illustration based on Microphysogobio chinssuensis. CPAP = central portion of anterior papillae; LPAP = lateral portion of anterior papillae; MP = medial pad; LL = lateral lobe; BB = barbel; UJ = upper jaw; LJ = lower jaw. The photo of Biwia zezera is provided by Seigo Kawase; the other photos and illustration were made by Zhi-Xian Sun.

Figure 5. The distributions of the Biwia – Microphysogobio complex and seven genera. A. The complex; B. Biwia; C. Microphysogobio; D. Huigobio; E. Platysmacheilus; F. Crossocheilogobio gen. nov.; G. Oriengobio gen. nov.; H. Mesophysogobio gen. nov.

Figure 10. The general view of Platysmacheilus exiguus, the type species of the genus Platysmacheilus, ASIZB 220879, 77.6 mm SL, collected from the Lijiang River in the Pearl River Basin, Pingle County, Guangxi Zhuang Autonomous Region, China. A. Lateral view; B. Dorsal view; C. Ventral view. Scale bar: 10 mm. Photographed by Zhi-Xian Sun.