Velella velella  

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.

 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.

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.

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.