Revisiting Bacan Island in the footsteps of Alfred Russel Wallace: unveiling the diversity of land snails (Mollusca, Gastropoda)

There are a total of 47 species from ten families of Gastropoda recorded on Bacan Island from 1861 to 1963 by 15 studies. In 2022, the island was revisited to investigate its current land snail diversity. Our survey yielded 555 individuals, which were identified and classified into 27 species from eleven families.

Among these, nine species were newly recorded on Bacan Island, bringing the total number of known land snail species to 56. These new records include a new species, Diancta batubacan Nurinsiyah, Prasetia, Mujiono & Heryanto, sp. nov. The most abundant species collected was Trochomorpha ternatana (family Trochomorphidae).

Differences in sampling locations and the extent of forest habitats in the surveyed areas may account for the different number of recorded species from previous and recent studies. Comprehensive systematic and standardised surveys are crucial for ensuring sampling completeness to further assess species endemism and biogeographic patterns. Furthermore, cataloguing all known species and resolving land snail’s systematics with integrative approach are important to understand the true diversity of land snail in this region.