Maritime ecosystems in Vietnam such as mangroves and mud flats are characterized by high biodiversity. However, elements of its biodiversity remain unclear and highly threatened. In this context, the assessment of rare species is a starting point to develop effective strategies for the conservation of entire ecosystems. In this paper, we report upon cryptic amphibolid gastropods in Vietnamese mangrove forests from the Mekong Delta. The snail fauna in the mangrove forests was previously known from published literature and three museum specimens as three amphibolid species, 'Amphibola' burmana, A. quadrasi, Salinator fragilis and 'S.' quadrasi. We investigated the identities of such snails using molecular and morphological methods. The amphibolids found in this survey were identified to belong to the genus Naranjia, new for Vietnam fauna. In addition, our phylogenetic analyses suggested that the Vietnamese amphibolids were the same species as Naranjia sp. reported from Thailand, and the amphibolids have both genetic and morphological polymorphisms within the population. These findings add to the great biodiversity of Vietnamese mangrove forests and mudflats.