The Eocene - Oligocene Transition was a period of major climatic and oceanographic change, resulting in widespread biotic overturning. However, the record of many marine organisms remains patchy. Planktic Mollusca (Pteropoda) from three cored boreholes spanning the Eocene/Oligocene boundary (EOB) in southern coastal Tanzania are represented by eight species, three of which are introduced as new: Heliconoides nikkieae sp. nov., Limacina tanzaniaensis sp. nov. and Limacina timi sp. nov. Three of the other species can only be identified in open nomenclature. The two most commonly occurring species, H. nikkieae and L. timi, straddle the EOB without noticeable loss in abundance. Two species, Limacina robusta (Eames, 1952) and L. tanzaniaensis disappear before the EOB. The species Bovicornu aff. eocenense Meyer, 1886 disappears shortly after the EOB. Two species were only found in a single sample each, in the Eocene part of the succession. Response to changing environmental conditions seems to be demonstrated by two or three of the pteropod species that become extinct before or shortly after the EOB.