Bashimyzon, Gong & Zhang, 2024

Gong, Xiong & Zhang, E, 2024, Bashimyzon cheni, a new genus and species of sucker loach (Teleostei, Gastromyzontidae) from South China, Zoosystematics and Evolution 100 (1), pp. 309-324 : 309

Bashimyzon gen. nov.

Figs 3D , 5 , 6 , 7

Type species.

Erromyzon damingshanensis Xiu & Yang, 2017: 893 (type locality: Qingshui-He, tributary to Hongshui-He of Zhu-Jiang basin, in Shanglin County, Guangxi Province)

Diagnosis.

Bashimyzon is distinct from all currently identified gastromyzontid genera except Erromyzon and Protomyzon in the presence of a gill opening restricted above pectoral-fin base (vs. gill opening elongate, extending downwards to or beyond the pectoral-fin insertion to the ventral surface of head), and pectoral fins backwards extending away from (vs. close to or beyond) pelvic-fin insertions. This new genus is separated from the two genera in having a larger (vs. small) gap between the posterior edge of eye and the vertical through the pectoral-fin insertion, with the gap length being nearly equal to (vs. less than) eye diameter (Fig. 3 ; Table 2 ) and a very small fleshy lobe (vs. a relatively large fleshy lobe or enlarged papillae; see Kottelat 2004: Page 306, figs 4-6, and Yang et al. 2012: Page 176, fig. 3; Table 2 ) posterior to the maxillary-barbel base.

Other characters useful for distinguishing Bashimyzon and Protomyzon include: upper and lower lips continuous around the corners of mouth (vs. discontinuous or interrupted by an arched blade-like structure; see Kottelat 2004: Page 306, figs 4-6), lower lip smooth (vs. papillated), and no externally distinct opercle (vs. present) (Table 2 ).

Bashimyzon is morphologically most similar to Erromyzon , but further differs from it in having a relatively larger (vs. smaller) gill opening (length 46.5-60.7% of HD vs. 25.8-44.9, and the distance from its lower extremity to the pectoral-fin insertion 3.6-16.1% of HD vs. 27.2-43.5; see Figs 3 , 4A, B ); fewer last branched pectoral-fin rays folded against the flank (3-4 vs. 7-8); and more posteriorly located pectoral fins (pre-pectoral length 17.0-22.3% of SL vs. 12.5-15.8; see Fig. 4C ), with a shorter (vs. longer) base (length 8.8-10.8% of SL vs. 13.9-17.4; see Fig. 4D ).

Etymology.

The generic name is derived from Bashi (岜是), the local name of the Damingshan Mountain in Zhuang nationality language, and myzon, a common suffix used in the Balitoridae . Gender masculine. The Chinese common generic name is here suggested as “岜是鳅属”.

Figures

Figure 3. Lateral views of heads for: Protomyzon aphelocheilus (A), Protomyzon borneensis (B), Erromyzon sinensis (C), and Bashimyzon damingshanensis (D). Arrows indicate extremities of gill openings, and blue dotted lines pass vertically through the pectoral-fin insertion and the posterior margin of eye, respectively.

Figure 4. Comparisons (linear regression) of some morphometric measurements between sampled species of Erromyzon [E. sinensis (blue dot), E. compactus (green diamond), E. yangi (grey star), and E. kalotaenia (yellow triangle)] and Bashimyzon [B. damingshanensis (ponk dot) and B. cheni (red square)]. A. Between GL % of HD and HD; B. Between G-P % of HD and HD; C. Between PPL % of SL and SL; and D. Between PBL % of SL and SL. GL - gill opening length; G-P - distance from the lowest extremity of gill opening to the pectoral-fin insertion; HD - head depth; PPL - pre-pectoral length; PBL - pectoral-fin base length; SL - standard length.

Figure 5. Dorsal (top), lateral (middle) and ventral (bottom) views of body in B. cheni, IHB 202109064273, holotype, 28.3 mm SL; China: Guangxi Province: Nanning City: Mashan County: Wuming-He, a stream tributary to You-Jiang of Zhu-Jiang basin, at Xinyang Village of Gulin Town.

Figure 6. Lateral view of freshly captured individual of A. B. damingshanensis, IHB 202109064259, topotype, 30.8 mm SL; China: Guangxi Province: Shanglin County: Qingshui-He at Naxue Village of Dafeng Town; and B. B. cheni, IHB 202109064273, holotype, 28.3 mm SL; China: Guangxi Province: Mashan County: Wuming-He at Xinyang Village of Gulin Town.

Figure 7. Ventral view of mouth in A. B. damingshanensis, IHB 202109064259, topotype, 30.8 mm SL; B. B. cheni, IHB 202109064273, holotype, 28.3 mm SL. fl - flesh lobe; lj - lower jaw; ll - lower lip; mb - maxillary barbel; rg - rostral groove; rf - rostral fold; rb - rostral barbels; sp - small papilla; uj - upper jaw; ul - upper lip.