D. João de Castro Bank (DJC) is a shallow seamount with hydrothermal activity located between the islands of Terceira and São Miguel, Azores (Portugal). A survey of the molluscan fauna was conducted in this peculiar habitat. We found a smaller number of molluscan taxa and a different community structure compared to shore environments on the Azores. This coincides with impoverished environmental settings at this location. Possible reasons such as the degree of isolation (inshore vs. offshore locations), geological age, and special ecological conditions related to seamounts and hydrothermal vents are discussed.