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Overview

Brief Summary

Biology

colonial
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The by-the-wind-sailor is not a jellyfish, but a colony of polyps which cohabitate. The famous Portuguese man-of-war is also such a colony. The polyps have various functions: eat, reproduce, deterrence. Together, they form an oval disk, which drifts on the waves. The by-the-wind-sailor has a triangular sail on this round disk. Using its sail, this organism travels the world seas. Sometimes, a group of them cross the ocean from the Caribbean region and land up along the European coasts.
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Comprehensive Description

Description

 Velella velella is a pelagic colonial hydroid. The float, which is an oval disc, is deep blue in colour and can be up to 10 cm in length. Short tentacles hang down into the water from the float. A thin semicircular fin is set diagonally along the float acting as a sail. This sail gives the animal both its scientific (i.e. from velum, a sail) and its common name, 'by-the-wind-sailor'. The direction of the sail along the float determines which way Velella velella will travel. If the sail runs north-west to south-east along the float it will drift left of the wind direction, if the sail runs south-west to north-east it will drift right of the wind direction. Velella velella feeds on pelagic organisms, including young fish, caught by stinging cells on its tentacles. The sea slug Fiona pinnata , sunfish Mola mola and violet snail Janthina janthina prey upon Velella velella.Velella velella is commonly found on the surface of the warmer waters of the World's oceans (Kirkpatrick & Pugh, 1984). McGrath (1985; 1992) reported large numbers of Velella velella washed up around the west coast of Ireland each year between 1976-1984, and again in 1992. In 1981 strandings were reported along the north Cornish coast, in north Devon, Lundy, Weston-Super-Mare and south-west Wales (Turk, 1982b). The Cornish Wildlife Trust Strandings Index (2002) has reports of two main stranding events per year in the winter, December-February, and late summer early autumn, August-September.

In 2002 there were numerous reports of washed up Velella velella. John White reported Velella velella washed up on a Sussex beach at Bognor rocks and Robert Harvey reported the species as far north as Kilmory Bay in the Sound of Jura (BMLSS, 2002a). Mike Bates reported Velella velella being washed up on the south of the Isle of Man, the last confirmed record previous to this was in 1954 (BMLSS, 2002a). At Millport, on the Isle of Cumbrae, Philip Smith reported small numbers of Velella velella washed ashore (BMLSS, 2002a), the first record from the Isle of Cumbrae despite there being a marine station there for over a hundred years (Smith, pers comm.). Edwards (1959) reported living specimens of Velella velella at Croy Sands, Turnberry Bay but no specimens were found on the Isle of Cumbrae despite a search.
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Biology/Natural History: This species is a puzzling one. It has long been regarded by many as a type of siphonophore; a pelagic colony of hydrozoan polyps similar to Physalia, the Portuguese man-of-war. Recent study suggests that, instead, it is a single very large hydrozoan polyp (Order Chondrophora), floating mouth downward and with a chitinous float and sail instead of a column. If so, it is an extremely large polyp for a hydrozoan. At any rate, the underside also includes many small polyps that bud off small medusae. The medusae (up to 1.5 mm tall) sink to as far as 2000m depth and produce gametes. The developing embryos develop floats and rise back to the surface. This species is oceanic, being usually found far offshore. The angled sail makes it sail at 45 degrees from the prevailing wind. Some have a sail angled to the left, others to the right. Off California the right-angled form prevails, and these remain offshore in the prevailing northerly winds. Strong southerly or westerly winds, however, may bring huge aggregations ashore. Velella have symbiotic algae (zooxanthellae) in their tissues, and also feed on zooplankton. They are eaten by pelagic gastropods such as some nudibranchs and bubble-rafting snails. The pelagic gooseneck barnacle Lepas anatifera occasionally attaches to the dead chitinous floats. This species has many nematocysts and a few people have reported feeling a sting, but I have handled many and have never been stung even slightly. The species feeds on fish eggs and crustacean larvae.

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Source: Invertebrates of the Salish Sea

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A small blue float made of concentric circles of gas-filled tubes. Up to 8 cm in diameter (usually 4 to 6), with a clear chitinous semicircular sail above and small tentacles below. The sail is angled left or right from the long axis of the float. Floats far offshore, but may be blown onshore in large numbers by some winds, especially in spring and early summer. Found worldwide in the temperate and tropical oceanic zone.
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Distribution

circum-(sub)tropical
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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 )

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Geographical Range: The species is pelagic and usually offshore, though thousands may be blown ashore by strong onshore winds (especially during El Nino), mostly during late spring and early summer. It occurs worldwide in temperate and tropical seas.

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Physical Description

Morphology

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

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Diagnostic Description

Description

Resembles Porpita but with triangular sail on upper surface, to 4 cm. Colour blue. Habitat: floating on sea surface. Distribution: pantropical (Richmond, 1997).
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Look Alikes

How to Distinguish from Similar Species: There are no similar species. The attached colonial hydrozoan Tubularia has a similarly structured (though much smaller) polyp but would not be mistaken for this species.
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Ecology

Habitat

Depth range based on 46 specimens in 1 taxon.
Water temperature and chemistry ranges based on 33 samples.

Environmental ranges
  Depth range (m): 0 - 2977
  Temperature range (°C): 2.536 - 24.988
  Nitrate (umol/L): 1.090 - 26.423
  Salinity (PPS): 31.235 - 36.547
  Oxygen (ml/l): 2.900 - 6.794
  Phosphate (umol/l): 0.074 - 1.602
  Silicate (umol/l): 1.840 - 28.123

Graphical representation

Depth range (m): 0 - 2977

Temperature range (°C): 2.536 - 24.988

Nitrate (umol/L): 1.090 - 26.423

Salinity (PPS): 31.235 - 36.547

Oxygen (ml/l): 2.900 - 6.794

Phosphate (umol/l): 0.074 - 1.602

Silicate (umol/l): 1.840 - 28.123
 
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pelagic
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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

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Depth range based on 46 specimens in 1 taxon.
Water temperature and chemistry ranges based on 33 samples.

Environmental ranges
  Depth range (m): 0 - 2977
  Temperature range (°C): 2.536 - 24.988
  Nitrate (umol/L): 1.090 - 26.423
  Salinity (PPS): 31.235 - 36.547
  Oxygen (ml/l): 2.900 - 6.794
  Phosphate (umol/l): 0.074 - 1.602
  Silicate (umol/l): 1.840 - 28.123

Graphical representation

Depth range (m): 0 - 2977

Temperature range (°C): 2.536 - 24.988

Nitrate (umol/L): 1.090 - 26.423

Salinity (PPS): 31.235 - 36.547

Oxygen (ml/l): 2.900 - 6.794

Phosphate (umol/l): 0.074 - 1.602

Silicate (umol/l): 1.840 - 28.123
 
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 Velella velella is a pelagic species but is occasionally seen washed up around Britain and Ireland.
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Depth Range: Float on surface (pleuston).

Habitat: Worldwide in temperate and tropical seas. Oceanic

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Trophic Strategy

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)

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Associations

Animal / predator
adult of Ianthina exigua is predator of Velella velella

Animal / predator
adult of Ianthina janthina is predator of Velella velella

Animal / predator
adult of Ianthina pallida is predator of Velella velella

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Life History and Behavior

Reproduction

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

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Velella velella

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 14
Species With Barcodes: 1
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Conservation

Conservation Status

US Federal List: no special status

CITES: no special status

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Wikipedia

Velella

Velella is a cosmopolitan genus of free-floating hydrozoans that live on the surface of the open ocean. There is only one known species, Velella velella, in the genus.[1] Velella velella is commonly known by the names sea raft, by-the-wind sailor, purple sail, little sail, or simply Velella.[2]

These small cnidarians are part of a specialised ocean surface community that includes the better-known cnidarian siphonophore, the Portuguese man o' war. Specialized predatory gastropod mollusks 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 Velella velella is in fact 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). Though the toxins in their nematocysts are effective against their prey, V. velella is essentially harmless to humans. While cnidarians all possess nematocysts, in some species the nematocysts and toxins therein are more powerful than other species. V. velella has nematocysts that 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.

Close-up of a Velella velella
Stranded Velella

Distribution and habitat[edit]

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 pleuston. 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.[5]

They have also been found as far as the west coast of Ireland, some having being washed up on the shoreline on Cruit Island and, November 2014, on Whitesands Bay beach, Pembrokeshire, West Wales. Several were seen on Pendower Beach, Roseland, Cornwall, also in November 2014.

In December 2014 on Woolacombe beach, North devon UK. The Coast line was scattered with thousands of stranded V.velella. And again on Marazion and Sennen beaches (West Cornwall) in early January 2015.

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.[6]

Life cycle[edit]

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.[7]

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.[7]

Systematics[edit]

The Porpitidae is a family of the Hydrozoa erected for three genera of hydroids that live floating free at the surface of the open ocean: Velella, Porpita and Porpema. 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 Siphonophora. A new order was established for these genera by Totton,[8] in 1954, called the Chondrophora, while at the same time, other authors favored again placing them in the Anthomedusae/Athecatae.[7] 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.

See also[edit]

References[edit]

  1. ^ WoRMS (2013). Velella velella (Linnaeus, 1758). In: Schuchert, P. (2013). World Hydrozoa database. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=117832 on 2013-04-23
  2. ^ Harrington Wells (1937). Seashore Life. Wagner Publishing Company, USA (see pages 138 and 144 in the 1942 edition)
  3. ^ Gosliner, T.M. (1987). Nudibranchs of Southern Africa page 127, ISBN 0-930118-13-8
  4. ^ Branch, G.M., Branch, M.L, Griffiths, C.L. and Beckley, L.E. (2010). Two Oceans: a guide to the marine life of southern Africa. Cape Town:Struik Nature. page 188. ISBN 9781770077720.
  5. ^ McNeill Alexander, R (2002). Principles of Animal Locomotion. Princeton University Press. ISBN 0-691-08678-8. 
  6. ^ http://www.jstor.org/action/viewCitation?doi=10.2307%2F25525026
  7. ^ a b c A. Brinckmann-Voss (1970). Anthomedusae/Athecatae (Hydrozoa, Cnidaria) of the Mediterranean. Part I. Capitata. Fauna e Flora del Golfo di Napoli 39. Stazione Zoologica. pp. 1–96, 11 pls. 
  8. ^ A. K. Totton (1954). Siphonophora of the Indian Ocean together with systematic and biological notes on related specimens from other oceans. Discovery Reports 27. pp. 1–162. 
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