When taxonomists classified the Velella velella as a Siphonophore, it was consisdered to be a much smaller species then most which comprise the order. Although these animals are tiny, they were described as having a complex body structure just as any other Siphonophore. The Velella is sometimes mistakenly called a 2 cm "portuguese man-of-war" and has cellophane like floats and erect triangular sails. The invertebrate is described as an upside-down polyp of a hydrozoa which did not settle to the bottom and grow sessile, but instead settled on the surface of the water and grew a float. The Velella is blueish to purple with a flat oval transparent float and an erect sail projecting vertically at an angle to the axis of its body. The projection of the sail is so that the animal can take the best advange of the wind, at any given moment. Older zoological opinions thought the Velella was a colony of specialized individuals like the "man-of -war", and that beneath its disk there was a single large feeding polyp surrounded by many reproductive polyps and a fringe of stinging polyps. More recent studies, however, have classified the Velella velella as a highly modified individual hydroid polyp, and not a colonial hydrozoa. Older zoological opinions classified the Velella velella as a Siphonophore, along with the Portuguese man-of-war and other colonial creatures. In contrast, recent taxonomists have classified the animal as a Chondrophore along with two or three uncommon relatives.
Within the species of Velella, the offspring show polymorphism in the orientation of their sails. A portion of the progeny have sails located from left to right away from the parent, and others have the sail from right to left. Both forms of Velella velella commonly occur. It is hypothesized that the different forms of this marine animal are mixed in the middle of the Pacific Ocean as larva, and that wind and wave patterns during development and growth cause them to move towards the coast. (Each form sending them in opposite directions). Near the end of spring, and early summer they arrive on the shores and are commonly cast up on the beaches of the Northern and Southern Hemispere. The distribution of its dimorphic form also takes place in the Atlantic and the Mediterranean.
(Russell-Hunter 1979, Ricketts,et al 1997)
Other Physical Features: ectothermic ; radial symmetry
This hydroid polyp remains afloat on the suface of the Pacific Ocean for most of its life. It never touches or even comes close to the ocean bottom, and the only stage in its life when it is completely submerged under water is the larval stage. The Velella velella begins its life in the middle of the Pacific Ocean, is brought by the wind to the shores, and is usually cast up on a beach where it dies and disentegrates. The Velella are most common on the high seas, in the warmer regions of the Southern and Northern Hemispheres.
(Russell-Hunter 1979)(Ricketts, et al 1997)
Aquatic Biomes: coastal
The Velella is found floating on the surface of the high seas, and is common in the warm seas.
(Ricketts, et al 1997)
Biogeographic Regions: atlantic ocean (Native ); pacific ocean (Native )
The Velella velella is a carnivorous hydroid polyp, feeding on small prey and fish that can be caught only immediately below the surface of the water. The Velella is limited to surface food because it is not a very big animal and its tentacles do not reach very far. Its mouth is located in the middle of the underside of its body and lacks tentacles.(Russell-Hunter 1979, Nichols 1979)
US Federal List: no special status
CITES: no special status
The Velella is carnivorous but is also the prey of local mollusks. The violet slug, a common predator of the Velella, floats independently as it feeds on Velella. (Ricketts,et al 1997)(Russell-Hunter 1979)
When biologists looked at the Velella velella as a colonial hydrozoan, the colonies were said to be hermaphroditic and the gonophores dioecious. The reproductive polyps were thought to produce medusa, which would break away from the colony and reproduce sexually, giving rise to planula larva. In recent studies, as biologist have examined the Velella as a single hydroid, reproduction still consists of an alternate generation between polyp and medusa stages. The life cycle: polyp-medusa-egg-planula-polyp.(Bayer and Harding 1968)(Ricketts, et al 1997)
Parental Investment: no parental involvement
Velella is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is Velella velella,[1] a cosmopolitan 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.[2]
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[3] and purple snails in the genus Janthina.[4]
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.
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.
Velella velella lives in warm and temperate waters in all the world's oceans. They live at the water/air interface, with the float above the water, and polyps hanging down about a centimetre below. Organisms that live partly in and partly out of the water like this are known as neuston.[5] Offshore boaters sometimes encounter thousands of V. velella on the water surface.
The small rigid sail projects into the air and catches the wind. However, Velella sails always align along the direction of the wind where the sail may act as an aerofoil, so that the animals tend to sail downwind at a small angle to the wind.[6] Having no means of locomotion other than its sail, V. velella is at the mercy of prevailing winds for moving around the seas, and are thereby also subject to mass-strandings on beaches throughout the world. For example, most years in the spring, there is a mass stranding that occurs along the West Coast of North America, from British Columbia to California, beginning in the north and moving south over several weeks' time. In some years, so many animals are left at the tide line by receding waves, that the line of dying (and subsequently rotting) animals may be many centimetres deep, along hundreds of kilometres of beaches. Mass strandings have been reported also on the west coast of Ireland,[7] and in Hayle, on the west coast of Cornwall in England.[8]
Like many Hydrozoa, Velella velella has a bipartite life cycle, with a form of alternation of generations. The deep blue, by-the-wind sailors that are recognized by many beach-goers are the polyp phase of the life cycle. Each "individual" with its sail is really a hydroid colony, with many polyps that feed on ocean plankton. These are connected by a canal system that enables the colony to share whatever food is ingested by individual polyps. Each by-the-wind sailor is a colony of all-male or all-female polyps. The colony has several different kinds of polyps, some of which are both feeding and reproductive, called gonozooids, and others protective, called dactylozooids.[9]
The gonozooids each produce numerous tiny jellyfish by an asexual budding process, so that each Velella colony produces thousands of tiny jellyfish (medusae), each about 1 mm high and wide, over several weeks. The tiny medusae are each provided with many zooxanthellae, single-celled endosymbiotic organisms typically also found in corals and some sea anemones, that can utilize sunlight to provide energy to the jellyfish. Curiously, although a healthy captive Velella will release many medusae under the microscope, and are expected to do the same in the sea, the medusae of Velella are rarely captured in the plankton and very little is known about their natural history. The medusae develop to sexual maturity within about three weeks in the laboratory and their free-spawned eggs and sperm develop into a planktonic larva called a conaria, which develops into a new floating Velella hydroid colony.[9]
The Porpitidae is a family of the Hydrozoa erected for two genera of hydroids that live floating free at the surface of the open ocean: Velella and Porpita. The systematic position of these peculiar genera has long been a topic of discussion among taxonomists who work with pelagic Cnidaria. The three genera were put in with athecate hydroids in the mid-to-late 19th century by some, whereas other authors at the time included them in the Siphonophorae. A new order was established for these genera by Totton,[10] in 1954, called the Chondrophora, while at the same time, other authors favored again placing them in the Anthomedusae/Athecatae.[9] Most authors in the past 40 years have accepted interpretation of these animals as unusual floating colonial athecate hydroids, which produce medusae clearly belonging in the Anthomedusae. Although the exact position of the family Porpitidae within the Athecatae/Anthomedusae is not yet clear, the order Chondrophora is no longer used by hydrozoan systematists.
Velella is a monospecific genus of hydrozoa in the Porpitidae family. Its only known species is Velella velella, a cosmopolitan 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.
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 and purple snails in the genus Janthina.
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.
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.
Stranded Velella 
Velella close-up
