Velella

Velella
Close-up of a Velella velella colony
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Order:	Anthoathecata
Family:	Porpitidae
Genus:	Velella Lamarck, 1801[1]
Species:	V. velella
Binomial name
Velella velella (Linnaeus, 1758)
Synonyms
List (Genus) Armenista Haeckel, 1888 Rataria Eschscholtz, 1829 Velaria Haeckel, 1888 (Species) Armenista sigmoides Haeckel, 1888 Holothuria spirans Forsskål, 1775 Medusa pocillum Montagu, 1815 Medusa velella Linnaeus, 1758 Rataria cordata Eschscholtz, 1829 Rataria mitrata Eschscholtz, 1829 Velella antarctica Eschscholtz, 1829 Velella aurora Eschscholtz, 1829 Velella australis de Haan, 1827 Velella caurina Eschscholtz, 1829 Velella cyanea Lesson, 1826 Velella emarginata Quoy & Gaimard, 1824 Velella indica Eschscholtz, 1829 Velella lata Chamisso & Eysenhardt, 1821 Velella limbosa Lamarck, 1816 Velella meridionalis Fewkes, 1889 Velella mutica Lamarck, 1801 Velella oblonga Chamisso & Eysenhardt, 1821 Velella oxyothone Brandt, 1835 Velella pacifica de Haan, 1827 Velella patellaris Brandt, 1835 Velella pyramidalis Cranch, 1818 Velella radackiana de Haan, 1827 Velella sandwichiana de Haan, 1827 Velella scaphidia Peron & Lesueur, 1807 Velella septentrionalis Eschscholtz, 1829 Velella sinistra Chamisso & Eysenhardt, 1821 Velella tentaculata Lamarck, 1801 Velella tropica Eschscholtz, 1829

Velella is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is Velella velella,^[2] a cosmopolitan (widely distributed) free-floating hydrozoan that lives on the surface of the open ocean. It is commonly known by the names sea raft, by-the-wind sailor, purple sail, little sail, or simply Velella.^[3]

This small cnidarian is part of a specialised ocean surface community that includes the better-known cnidarian siphonophore, the Portuguese man o' war. Specialized predatory gastropod molluscs prey on these cnidarians. Such predators include nudibranchs (sea slugs) in the genus Glaucus^[4] and purple snails in the genus Janthina.^[5]

Each apparent individual is a hydroid colony, and most are less than about 7 cm long. They are usually deep blue in colour, but their most obvious feature is a small stiff sail that catches the wind and propels them over the surface of the sea. Under certain wind conditions, they may be stranded by the thousand on beaches.^[6]

Like other Cnidaria, Velella velella are carnivorous. They catch their prey, generally plankton, by means of tentacles that hang down in the water and bear cnidocysts (also called nematocysts). The toxins in their nematocysts are effective against their prey. While cnidarians all possess nematocysts, in some species the nematocysts and toxins therein are more powerful than other species. V. velella's nematocysts are relatively benign to humans, although each person may respond differently to contact with the nematocyst toxin. It is wise to avoid touching one's face or eyes after handling V. velella, and itching may develop on parts of the skin that have been exposed to V. velella nematocysts.