Reassessment and systematic position of the sinistral snails of genus Hemiplecta from Thailand (Eupulmonata: Ariophantidae), with description of two new species

Abstract

Indochina land snails of the family Ariophantidae are in need of thorough systematic revision. Here we comprehensively revise the systematics of the large-shelled, sinistral (counterclockwise) coiling snails from Thailand and Peninsular Malaysia. Molecular phylogeny based on mitochondrial (coi and 16S) and nuclear (28S) gene sequences demonstrates that these sinistral snails are not members of Dyakiidae as previously thought, but instead are more closely related to the genus Hemiplecta in the family Ariophantidae. Comparative morphology also reveals similarity of reproductive organ features (globular gametolytic organ, well-developed dart apparatus, and lack of amatorial organ complex). Based on this evidence, we propose to transfer these sinistral snails to the genus Hemiplecta. Molecular phylogenetic analyses further strongly support the monophyly of this sinistral lineage with respect to other members of Hemiplecta. This monophyletic clade consists of five members including three species that were previously classified as “Dyakia”, H. lahatensis, H. retrorsa and H. salangana, and two new species described herein, H. ligorica n. sp. and H. thailandica n. sp. This study also suggests that the anatomy of the gametolytic organ in the genus Hemiplecta corresponds well with the phylogenetic relationships and appears to be a taxonomically informative character, while the penial verge has little utility for generic recognition.

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

“…Ho 1995. Thiele (1931), Zilch (1959, 2 = Blanford and Godwin-Austen (1908), 3 = Wiegmann (1898), Sarasin and Sarasin (1899), 4 = Godwin-Austen (1899), and 5 = Sutcharit et al (2021), present study. Shell.…”

“…These characters were accepted as being more reliable than the shell morphology, and were followed until recently (Blanford and Godwin-Austen 1908;Thiele 1931;Zilch 1959;Schileyko 2002). The recent phylogeny of some Indochinese Hemiplecta (including the type species) confirm that they are monophyletic and are comprised not only of dextral species but also several sinistral species that were previously included in the Dyakia Godwin-Austen, 1891 (see Sutcharit et al 2021). In addition, the modern systematic revision of various helicarionoid groups has illustrated the taxonomic importance of reproductive characters for distinguishing taxa at both the generic and specific levels (i.e.…”

“…Descriptive terms are oriented with reference to the genital orifice. Abbreviations follow Godwin-Austen (1900, 1919, Schileyko (2002), Pholyotha et al (2020) and Sutcharit et al (2021): ag, albumin gland; aldl, anterior left dorsal lobe; an, anus; at, atrium; da, dart apparatus; dp, dart papilla; e, epiphallus; ec, epiphallic caecum; fl, flagellum; fo, free oviduct; gs, gametolytic sac; h; heart; hd, hermaphroditic duct; hg, hermaphroditic gland; k, kidney; lsl, left shell lobe; ov, oviduct; p, penis; pg, prostate gland; pldl; posterior left dorsal lobe; pr, penial retractor muscle; ps, penial sculpture; psh, penial sheath; puv, pulmonary vein; pv, penial verge; r, rectum; rdl, right dorsal lobe; rsl, right shell lobe; ur, ureter; v, vagina; vd, vas deferens.…”

“…As currently understood, the diverse ariophantid snail genus Hemiplecta Albers, 1850 consists of around 50 dextral species as well as five sinistral species (MolluscaBase 2020; Sutcharit et al 2021). They are distributed from Indochina through the Sunda Islands to New Guinea (Zilch 1959;Schileyko 2002), with vague records from the Maldives and Kerala, India (Schileyko 2002;Ramakrishna et al 2010).…”

“…In Thailand, thirteen nominal (dextral and sinistral) species have previously been attributed to Hemiplecta, many of which were uncritically listed in compilations derived from earlier literature (see Panha 1996;Hemmen and Hemmen 2001) and all are based only on shell morphology. Among these, four sinistral species previously attributed to Dyakia have been revised and transferred to Hemiplecta (see Sutcharit et al 2021). The other nine dextral species have been re-classified based on analyses of molecular phylogeny and genitalia morphology.…”