Molecular phylogeny of the limestone karst–associated land snail genus Siamochlamys (Eupulmonata: Helicarionidae), with descriptions of two new species from Thailand

Abstract

We present a comprehensive systematic revision of the monotypic helicarionid genus Siamochlamys, in Thailand. Based on extensive land snail collections from across Thailand, we describe two new species (S. isanensis sp. nov. and S. lannaensis sp. nov.) and reassign two previously overlooked species S. mitiuscula (Martens, 1867) comb. nov. and S. sinulabris (Martens, 1865) comb. nov. to this genus. Species boundaries were evaluated using an integrative approach that combined comparative morphology and DNA sequence data (COI, 16S rRNA, 28S rRNA). Phylogenetic analyses confirm the monophyly of the genus within the Helicarionidae, and divide it into two groups: one comprising S. mitiuscula, S. sinulabris, and S. panhai, and another containing S. isanensis sp. nov. and S. lannaensis sp. nov. Within the first group, S. mitiuscula and S. sinulabris form a strongly supported clade closely related to S. panhai, whereas the relationships within the second group remain unresolved. Morphologically, the first group differs by a unique combination of characters, including a larger shell with a wider umbilicus and reproductive traits such as the presence of a flagellum and a clearly differentiated boundary between penis and proximal epiphallus. The discovery of these land snails increases the number of Siamochlamys species known from Thailand to five, thereby enhancing our understanding of the country’s endemic malacofauna.