Janthina janthina

Janthina janthina
A live Janthina janthina (with bubble raft) that has been swept up onto a beach in Maui, Hawaii. This is the normal view from above: the spire of the shell is held pointing down like this when the animal is floating on the surface of the ocean water.
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Caenogastropoda clade Hypsogastropoda informal group Ptenoglossa
Superfamily:	Epitonioidea
Family:	Janthinidae
Genus:	Janthina
Species:	J. janthina
Binomial name
Janthina janthina (Linnaeus, 1758)
Synonyms
Helix janthina Linnaeus, 1758 Janthina affinis Reeve, 1858 Janthina africana Reeve, 1858 Janthina alba Ant*on, 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 A. 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

clade Hypsogastropoda
informal group Ptenoglossa

Janthina janthina, common name the violet sea-snail or common violet snail, is a species of holoplanktonic sea snail, a marine gastropod mollusk in the family Janthinidae, the violet snails or purple storm snails.

This species is found worldwide in the warm waters of tropical and temperate seas, floating at the surface. They are often found in large groups and sometimes become stranded on beaches when they are blown ashore by strong winds.

These snails are a unique part of the pleuston, organisms living on or at the very 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.

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

Janthina janthina is a member of the Janthinidae family, snails that trap air bubbles with a layer of clear chitin to maintain their positions at the surface of the ocean where they are predatious on the hydrozoans. 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.

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. The animal has a large head on a very flexible neck. The eyes are small and are situated at the base of its tentacles.

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Wikipedia