Janthina janthina is a species of holoplanktonic sea snail, a marine gastropod mollusk in the family Epitoniidae. Its common names include violet sea-snail, common violet snail, large violet snail and purple storm snail.^[2]

Quick Facts Janthina janthina, Scientific classification ...

Janthina janthina
Janthina janthina
A live Janthina janthina, with bubble raft, that has been washed up in Maui, Hawaii. This is the normal view from above: the spire of the shell is held pointing down when the animal is floating on the surface of the ocean.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subclass:	Caenogastropoda
Superfamily:	Epitonioidea
Family:	Epitoniidae
Genus:	Janthina
Species:	J. janthina
Binomial name
Janthina janthina (Linnaeus, 1758)
Synonyms[1]
Helix janthina Linnaeus, 1758 Janthina affinis Reeve, 1858 Janthina africana Reeve, 1858 Janthina alba Anton, 1838 Janthina balteata Reeve, 1858 Janthina bicolor Menke, 1828 Janthina bicolor var. major Monterosato, 1878 Janthina bicolor var. minor Monterosato, 1878 Janthina britannica Forbes & Hanley, 1853 Janthina carpenteri Mørch, 1860 Janthina carpenteri var. contorta Tryon, 1887 Janthina casta Reeve, 1858 Janthina coeruleata Reeve, 1858 Janthina communis Lamarck, 1799 Janthina costae Mørch, 1860 Janthina depressa Reeve, 1858 Janthina fibula Reeve, 1858 Janthina fragilis Lamarck, 1799 (junior synonym) Janthina fragilis var. spiraelata Mørch, 1860 Janthina grandis Reeve, 1858 Janthina involuta Reeve, 1858 Janthina orbignyi Mørch, 1860 Janthina penicephela Peron, 1824 Janthina planispirata Adams & Reeve, 1848 Janthina roseala Reeve, 1858 Janthina rotundata Dillwyn, 1840 Janthina smithiae Reeve, 1858 Janthina striulata Carpenter, 1857 Janthina striulata var. contorta Carpenter, 1857 Janthina trochoidea Reeve, 1858 Janthina violacea Bolten, 1798 Janthina vulgaris Gray, 1847

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This species is found worldwide in the warm waters of tropical and temperate seas, floating at the surface.^[3] More specifically, the species is located in the tropical and subtropical Atlantic, Indian and Pacific oceans.^[4] They are often found in large groups and sometimes become stranded on beaches when they are blown ashore by strong winds.^[3] The snails are a unique part of the neuston, organisms which live on or near the surface of the water, because of their relatively large size. They have veliger, or free swimming larvae, but the adults do not swim, and cannot create their rafts, except at the surface where air bubbles are available.^[5]

These snails are pelagic, drifting on the surface of the ocean, where they feed upon pelagic hydrozoa, especially the by-the-wind sailor, Velella velella, and the Portuguese man o' war, Physalia physalis.

J. janthina is a member of the family Janthinidae, snails that trap air bubbles to maintain their positions at the surface of the ocean, where they are predators on hydrozoa.^[6] The air bubbles are stabilized by the secretion of amphiphilic mucins which have evolved from epitoniid egg masses.^[7] This passive flotation is a particularly resource-efficient form of animal locomotion.^[8] In addition to the bubble raft, only the veliger, or larval stage, has an operculum, and the shell is paper-thin to allow the animal to float upside down at the surface.^[3][9]

The snail's shell is reverse countershaded, because of its upside-down position in the water column. There is a light purple shade on the spire of the shell, and a darker purple on the ventral side.^[9] The animal has a large head on a very flexible neck. The eyes are small and are situated at the base of its tentacles. The shell, which is violet, with a paler upper surface, is almost smooth, with a slightly depressed-globose shape.^[6] It is thin and delicate, and is without an operculum.^[3] The height of the species shell is up to 38 mm, the width to 40 mm.^[6]

The snail begins life as a male and later changes into a female. The eggs are held by the female until they develop into the larval form.^[3]