Limacina

Limacina is a genus of small pelagic sea snails, commonly called sea butterflies, in the family Limacinidae. Members are holoplanktonic gastropods whose entire life cycle occurs in the open ocean. They possess a transparent, coiled shell made of aragonite and a body with wing-like parapodia used for swimming.

They are distributed in cold, temperate, and polar seas worldwide, with several species typical of Arctic and subarctic waters and others in the Southern Ocean and North Atlantic. They inhabit the upper water column, typically from the surface to a few hundred meters, and may participate in vertical migrations.

They feed on microalgae and phytoplankton, capturing particles with mucus nets and/or ciliary action. Reproduction is sexual, with adults producing free-swimming veliger larvae that develop into juvenile snails.

As a prominent component of pelagic zooplankton, they are prey for fishes, seabirds, and marine mammals. Their aragonite shells contribute to carbon cycling when they sink to the seabed. They are widely used as indicators of ocean health and are considered particularly vulnerable to ocean acidification, which can reduce calcification and affect distribution and survival.

The genus comprises multiple species, including Limacina helicina, commonly called the Arctic sea butterfly, and Limacina retroversa in the North Atlantic, among others.