Bakyietaia Zhang, Yen & von Rintelen, 2025

Genus Bakyietaia Zhang, Yen & von Rintelen gen. nov.

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Type species

Vivipara polyzonata Frauenfeld, 1862 View in CoL .

Diagnosis

Adult shell mostly medium in size for the family (20~ 30 mm in height), sturdy. Each teleoconch whorl with three to five (mostly three) strong smooth keels. Umbilicus covered by crescent-shaped callus formed from columellar lip. Operculum with small nuclear region (around 1/4 to 1/5 of inner opercular region) with shiny grains or veins. Inner marginal teeth of radula nearly half of outer marginal teeth in width. Mantle margin simple and smooth.

Etymology

‘Bakyie’ is derived from ‘Bakyied’ in the Zhuang Language (百ṉ in Chinese), referring to various ethnic groups living in South China and northern Vietnam; ‘taia’ refers to its similarity to the viviparid genus Taia Annandale, 1918 . The recommended Chinese name is ṉ田ª.

Description

Shell mostly medium in size for the family (20~ 30 mm in height), thin to thick, solid, conical; apex acute, teleoconch whorls with three to four smooth primary keels, with one to two weaker smooth secondary keels located between suture and first keel, base of shell with one to six keels, keels usually darker than rest of shell surface; recurved columellar lip from different growing periods sometimes forming a crescent-shaped callus, normally covering umbilicus; operculum with smooth exterior surface and a relatively small nuclear region (around 1/4 to 1/5 of inner opercular region) with shiny grains or veins; radula with narrow inner marginal teeth (narrower than lateral teeth) and wide outer marginal teeth (almost same as lateral teeth in width), outer marginal teeth with 15 to 43 tiny cusps; mantle margin simple and smooth.

Remarks

Previously described species in this genus have hitherto mostly been assigned to the genus Angulyagra , while a few have been assigned to the genera Taia or Sinotaia . Species of Bakyietaia gen. nov. can be easily distinguished from species of Angulyagra based on their smaller, more solid and heavier shell with a crescent-shaped callus-like structure formed from the columellar lip covering the umbilicus; the characters of the operculum and the radula of Bakyietaia are obviously distinct from those of Angulyagra ; the mantle margin of species of Bakyietaia is smooth and does not bear the ‘finger-shaped processes on the margin’ of the mantle as observed in Angulyagra . Taia , Sinotaia , Anulotaia and some species of Filopaludina have a similar medium-sized and solid conical shell ( Fig. 5 View Fig ).

Bakyietaia gen. nov. can be distinguished from these genera based on the following combination of characters: teleoconch whorls with three smooth primary keels and one to two weaker secondary keels, mostly darker in colour than the other part of shell surface; recurved columellar lip from different growing periods usually completely covering umbilicus; inner marginal teeth narrow, outer marginal teeth wide and with 15 to 30 tiny cusps. The COI tree supports the notion that Bakyietaia is a lineage distinct from Taia , Sinotaia , Anulotaia , Filopaludina and Angulyagra costata .

We have checked the type specimens of Angulyagra thersites (Reeve, 1864) from Hongkong, China, and we are confident that it should be assigned to the genus Sinotaia . A future taxonomic revision of this species should be based on a systematic study of Sinotaia . In addition, Bakyietaia gen. nov. is usually dominant and the only viviparid group in its habitat. Species of Bakyietaia are found to co-occur with widely-distributed species of Sinotaia in some localities, but seldom found to co-occur with species of other genera of Viviparidae .

Habitat and distribution

Found in many kinds of lentic and lotic freshwater habitats ( Fig. 6 View Fig ). Native to southern China, northern to central Vietnam and Laos.

Identification key to species of Bakyietaia gen. nov.

1. Shell rounded, primary keels weak, height and width isometric ...................................................... 2

– Shell conical, shell height obviously larger than width .................................................................... 3

2. 29–43 cusps in outer marginal teeth .......................... B. subcostata (Gray, 1833) gen. et comb. nov.

– 14–15 cusps in outer marginal teeth .... B. chenghuang Zhang, Yen & von Rintelen gen. et sp. nov.

3. Three to five weak primary keels on body whorl, sometimes as smooth as spiral lines .................. 4

– Three to five strong primary keels on body whorl ............................................................................ 8

4. Shell height usually less than 20 mm, spiral whorls lower, shoulder angular ..................................... ..................................................................... B. luikongi Yen, Zhang & von Rintelen gen. et sp. nov.

– Shell height greater than 20 mm, spiral whorls higher, shoulder rounded ....................................... 5

5. Whorls nearly cylindrical, weak keel above suture, outer lip not angular .......................................... ..................................................................... B. naiadica Zhang, Yen & von Rintelen gen. et sp. nov.

– Whorls nearly trapezoidal, prominent keel above suture, outer lip angular ..................................... 6

6. Whorls not inflated, shoulder rounded, 26–29 cusps in outer marginal teeth ..................................... ................................................................... B. fontinalis Zhang, Yen & von Rintelen gen. et sp. nov.

– Whorls inflated, shoulder angular, 19–24 cusps in outer marginal teeth .......................................... 7

7. Prominent keel above suture, distributed in northern Hainan Island, China...................................... ....................................................................................... B. mutica (Kobelt, 1909) gen. et comb. nov.

– Moderate keel above suture, distributed in southern Hainan Island, China....................................... ............................................................... B. luuemxlong Zhang, Yen & von Rintelen gen. et sp. nov.

8. Shell height greater than 30 mm, solid and thick, whorls inflated, shoulder angular ......................... ................................................................................... B. duchieri ( Fischer, 1898) gen. et comb. nov.

– Shell height usually smaller than 30 mm.......................................................................................... 9

9. Shell height usually less than 20 mm, whorls inflated, prominent keel above suture, 28–30 cusps in outer marginal teeth ...................................... B. guangdungensis ( Kobelt, 1906) gen. et comb. nov.

– Shell height between 20 and 30 mm............................................................................................... 10

10. Shell thin, shoulder more angular, whorls inflated ..........................................................................11

– Shell thick, shoulder more rounded, whorls not inflated ................................................................ 13

11. Moderate keel above suture, outer lip more rounded, distributed in northern Vietnam and across the border in SW Guangxi, China.......................... B. polyzonata ( Frauenfeld, 1862) gen. et comb. nov.

– Prominent keel above suture, outer lip more angular ..................................................................... 12

12. More inflated whorls and more prominent keel at suture, distributed in central Vietnam.................. .................................................................. B. indrapura Zhang, Yen & von Rintelen gen. et sp. nov.

– Less inflated whorls and less prominent keel at suture, distributed in Guangdong and across the border in SE Guangxi, China.............. B. avisvenatoris Yen, Zhang & von Rintelen gen. et sp. nov.

13. Spire low, W/H 0.72~0.74 .............................................................................................................. 14

– Spire high, W/H 0.68~0.70 ............................................................................................................. 15

14. Primary keels less prominent, outer lip thin, 26–27 cusps in outer marginal teeth, distributed in nothern Guangxi, China.......................... B. liusanjieae Zhang, Yen & von Rintelen gen. et sp. nov.

– Primary keels more prominent, outer lip thick, 24–27 cusps in outer marginal teeth, distributed in eastern Guangxi and central Guangdong, China................................................................................ ........................................................... B. liangzhuorum Yen, Zhang & von Rintelen gen. et sp. nov.

15. Moderate keel above suture, 18–25 cusps in outer marginal teeth, mostly distributed in Guangdong, China............................................................................ B. wilhelmi * ( Yen, 1939) gen. et comb. nov.

– Prominent keel above suture, 23–28 cusps in outer marginal teeth, not occurring in Guangdong, China............................................................................................................................................... 16

16. 23–24 cusps in outer marginal teeth, distributed in southern Guangxi and northern Hainan Island, China................................................................. B. boettgeri (Möllendorff, 1890) gen. et comb. nov.

– 26–28 cusps in outer marginal teeth, distributed in Vietnam, across the border in western Guangxi and western Hainan Island, China............ B. jingweiae Yen, Zhang & von Rintelen gen. et sp. nov.

* In light of the high phenotypic plasticity in B. wilhelmi , incorporates only the morphological traits of the holotype. DNA barcoding may be required to confirm the species identity of other morphological variations of this species.