Limacina helicina is a species of small swimming planktonic sea snail, in the family Limacinidae.

[15] However, at the species level the geographical distribution is considered to be bipolar, as it occurs in both the Arctic and Antarctic oceans.

Hunt 2010 found a 33.56% difference in cytochrome c oxidase subunit I (COI) gene sequences between the "Limacina helicina" which were collected from the Arctic and the Antarctic oceans.

[11] In this species, the color of the soft parts is dark purple or violet, with paler pellucid (translucent) parapodia.

[15] Species of the clade Thecosomata produce a fragile external calcium carbonate shell, which could serve as a ballast enabling large vertical migrations and as a protection against predators.

[10] Because of its highly soluble[11] aragonite shell and polar distribution, Limacina helicina may be one of the first organisms affected by ocean acidification, and it is therefore a key indicator species of this process.

[15] Based on laboratory experiments, they are able to precipitate calcium carbonate at low aragonite saturation state.

[11] Limacina helicina seems to be relatively more resilient to elevated concentration of carbon dioxide (CO2) than other aragonitic organisms such as corals.

[11] Laboratory experiments results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH.

[10][11][15] Researchers found 24-53% individuals of Limacina helicina with shells damaged by dissolution off the U.S. West Coast in 2011.

[28] Gilmer & Harbison (1991)[13] hypothesized that Limacina helicina are "web trappers", who are also chemically attracting their motile prey.

[13] Major parts of the food of Limacina helicina include tintinnid (Tintinnida), small crustaceans - copepods (Copepoda) and juvenile specimen of its own species (cannibalism).

[13] Danish zoologist Johan Erik Vesti Boas reported diatoms (Bacillariophyceae), dinoflagellates (Dinoflagellata) and tintinnids in the digestive system of Limacina helicina in 1888 already.

[13] All experiments performed on Limacina helicina in the laboratory were done on starved specimens, because they do not feed in unnatural conditions.

[28] Limacina helicina plays an important role in the marine food web as a major dietary component for predators such as large zooplankton, herring Clupea sp.,[22] chum salmon Oncorhynchus keta,[22] pink salmon Oncorhynchus gorbuscha,[22] rorquals,[22][27] Phoca hispida[27] and other seals[27] and birds.

[34] Limacina helicina possesses a pair of flexible, wing-like appendages called parapodia which it beats in a complex 3D stroke pattern which resembles the wing kinematics of flying insects.

The sea butterfly uses a high angle of attack of approximately 45-50 degrees to generate lift, and it beats its wings 4 to 10 times per second.

It propels itself using a version of the clap and fling mechanism described by Torkel Weis-Fogh in small insects such as thrips.

[37][38] Another aspect of locomotion by Limacina helicina is the extreme, forward-back pitching (called hyper-pitching) which it experiences during each half-stroke of its wings.