At high latitudes, thecosome pteropods (marine pelagic mollusks) can dominate zooplankton communities and are important food web components. Due to their calcium carbonate shell made of aragonite, they significantly contribute to ocean carbon flux and are particularly vulnerable to ocean acidification. Furthermore, aragonite undersaturation (Ωar < 1) events are projected to rapidly increase in frequency and duration in the Antarctic Weddell Sea by 2050 due to uptake of increasing amounts of anthropogenic CO2. This potentially perils thecosomes by inducing shell dissolution. The project aim was to describe the importance of thecosome pteropods in terms of their biomass contribution relative to that of other mesozooplankton groups in the Weddell Sea pelagic ecosystem and to describe the current shell dissolution state of thecosome pteropods in relation to prevailing ocean carbonate chemistry conditions as a benchmark for possible future monitoring of ongoing ocean change processes. This dataset includes size/shell mass data of individual shells of thecosome specimen of the species Limacina helicina antarctica that were usually collected from 500–0 m depth during PS111 at the eastern Weddell Sea Shelf and the Filchner-Ronne ice shelf.