Velella velella (Linnaeus, 1758)
Common name(s) By-the-wind sailor
|Synonyms: Velella lata||
Top view of Velella velella. Note blue disk and clear, angled chitinous float.
Order Chondrophora (previously Siphonophora)
Underside of Velella velella, showing short tentacles.
|Photos by: Dave Cowles at San Simeon, CA|
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. The 'bluebottle' found for example in Australia is a similar color of blue but has an inflated float like a Portuguese man-of-war.
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.
Depth Range: Float on surface (pleuston).
Habitat: Worldwide in temperate and tropical seas. Oceanic
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.
|Main Page||Alphabetic Index||Systematic Index||Glossary|
Brusca and Brusca, 1990
Morris et al., 1980
Francis, Lisbeth, 1985. Design of a small cantilevered sheet: the sail of Velella velella. Pacific Science 39: 1 pp. 1-15
Francis, Lisbeth, 1991. Sailing downwind: Aerodynamic performance
of the Velella sail.
Journal of Experimental Biology 158: 117-132
In the summer of 2014 a huge number of by-the-wind sailors were washed up all up and down the Oregon and Washington open coast. Here is a collection of several at the high tide wrack line at Rialto Beach.
Photo by Dave Cowles, August 2014