Janbinmorpha Pholyotha & Sutcharit & Panha & Tongkerd 2024, gen. nov.

Janbinmorpha Pholyotha & Panha gen. nov. Type species. Trochomorpha sculpticarina Martens, 1883; here designated. Etymology. The name combines “ Janbin ” in reference to the shape of an unidentified flying object (UFO) in the Thai language, and similar to the shell shape of this new genus, and “ morpha ” in reference to the similarity of shell morphology between this new genus and the genus Trochomorpha. Diagnosis. Shell dextral, umbilicated, depressed, lenticular, ribbed, with keeled last whorl. Animal with three dorsal lobes; foot tripartite; caudal foss present; caudal horn very reduced. Genitalia having epiphallic caecum, flagellum and dart apparatus; proximal epiphallus encircled with thickened muscular epiphallic sheath; gametolytic organ without duct and gametolytic sac consisting of two bulbs. Radula with tricuspid central tooth; unicuspid or bicuspid lateral teeth; unicuspid marginal teeth. Description. See below under the type species. Constituent species. This new genus contains only the type species, J. sculpticarina comb. nov. Distribution. Currently known only from the Malay Peninsula. Remarks. Janbinmorpha gen. nov. is clearly discriminated from all other Southeast Asian limacoid genera (e. g., Hemiplecta, Holkeion Godwin-Austen, 1908, Siamoconus Pholyotha in Pholyotha et al. 2023 a, Videna and Trochomorpha) by the shape of the gametolytic sac and by the attachment of the penial retractor muscle. This new genus has no gametolytic duct and the gametolytic sac is divided into two lobes, while the gametolytic sac of all other limacoid genera is not divided into two lobes and most of them have a gametolytic duct. The penial retractor muscle of this new genus is attached to two regions (epiphallic caecum and epiphallic sheath), while all other limacoid genera have the retractor muscle attached to either the epiphallic caecum or epiphallus (Blanford and Godwin-Austen 1908; Solem 1966; Schileyko 2002 a, b, 2003; Sutcharit et al. 2020 a, 2021; Sutcharit and Panha 2021; Pholyotha et al. 2021 b, c, 2022 a, b, 2023 b, c). Janbinmorpha gen. nov. also differs from Videna in having a long dart apparatus and the position of gametolytic organ on female side, while the latter genus has no dart apparatus and gametolytic duct opening into the base of the penis (Schileyko 2002 a). Janbinmorpha gen. nov. is conchologically very similar to the Indian helicarionoidean genus Sivella Blanford, 1863. However, this new genus differs by having a long dart apparatus, a straight epiphallic caecum, and no gametolytic duct. In comparison, Sivella has a relatively short gametolytic duct and a subglobular gametolytic sac, and does not have a dart apparatus or epiphallic caecum (Godwin-Austen 1918; Schileyko 2003). In addition, the molecular phylogeny (Fig. 1) supports a distinct lineage of the monotypic Janbinmorpha gen. nov. from genera Hemiplecta, Siamoconus, Videna and Trochomorpha. Currently, genetic sequences of Holkeion and Sivella are not available in the online GenBank sequence database for phylogenetic analysis.