Limacina helicina is a species of small swimming planktonic sea snail in the family Limacinidae, which belong to the group commonly known as sea butterflies (Thecosomata). Limacina helicina is a keystone species of mesozooplankton in Arctic pelagic ecosystems.

The zooplankter L. helicina is a pelagic thecosomatous sea snail known as the sea butterfly. Limacina helicina is ecologically important for the large biomass it maintains in polar pelagic ecosystems.

Limacina helicina is the dominant pelagic gastropod mollusc species in temperate and polar ecosystems, where it contributes significantly to food webs and vertical flux.

The shelled pteropod (sea butterfly) Limacina helicina is currently recognised as a species complex comprising two sub-species and at least five ‘‘forma’’. However, at the species level it is considered to be bipolar, occurring in both the Arctic and Antarctic oceans.