Hemiplecta Albers, 1850

Sutcharit, Chirasak & Panha, Somsak, 2021, Systematic review of the dextral Hemiplecta Albers, 1850 (Eupulmonata, Ariophantidae) from Thailand with description of a new species and list of all the Indochinese species, ZooKeys 1047, pp. 101-154 : 101

Genus Hemiplecta Albers, 1850

Hemiplecta Albers, 1850: 60, 61. Albers 1860: 52, 53. Godwin-Austen 1888b: 155-157. Godwin-Austen 1898: 70, 71. Zilch 1959: 317. Schileyko 2002: 1282, 1283.

Nanina (Hemiplecta) - Adams and Adams 1858: 222. Nevill 1878: 46-48.

Koratia Godwin-Austen, 1919: 202. Type species: Helix distincta Pfeiffer, 1850, by monotypy. Schileyko 2002: 1281, 1282.

Hemiplecta (Koratia) - Zilch 1959: 317. Vaught 1989: 97.

Ariophanta (Semperia) Godwin-Austen, 1898: 82 [non Crosse 1867: 74, 75]. Type species. Helix retrorsa Gould, 1843; by original designation.

Type species.

Helix humphreysiana Lea, 1840; subsequent designation by Martens in Albers (1860).

Diagnosis.

Shell dextral or sinistral, medium to large in size (width about 25 to 75 mm) and monochrome to with stripes, or banding patterns. Apertural lip simple to slightly thickened in adult snails; umbilicus open. Genitalia include penial sheath, straight or coiled epiphallic caecum and short flagellum; penial verge may be present or absent. Dart apparatus well developed; gametolytic sac bulbous to elliptical-shaped (without distinct duct). Mantle edge well developed with or without shell lobes. Jaw smooth (without vertical ribs) and crescentic. Radula with unicuspid central teeth, and bicuspid lateral and marginal teeth.

Remarks.

Due to the high degree of similarity in shell morphology, the specific and generic classification within Ariophantidae is usually problematic. There are at least three nominal genera that are often confused, Nanina Gray, 1834, Ariophanta Des Moulins, 1829 and Cryptozona Mörch, 1872. The genitalia have proved to be the distinguishing characters for specific or generic recognition among the Ariophantidae ( Laidlaw 1932a; Solem 1966; Sutcharit and Panha 2008). However, only a few species of each genus have been anatomically examined. Based on this limited anatomical information, the unique characters taken from the type species are summarized in Table 1 . The genus Hemiplecta can be differentiated from these three genera by lacking a gametolytic duct, while the others possess a short to long gametolytic duct. Hemiplecta also differs from Ariophanta and Cryptozona by having unicuspid central teeth, very short or absent flagellum, and a mantle edge with shell lobes; while the latter two genera have tricuspid central teeth, long flagellum, and a mantle edge without shell lobes. In addition, Hemiplecta can be distinguished from Nanina by its short flagellum (Table 1 ).

Dextral species in Thailand