Velella velella
Distribution:
Oceanic worldwide in temperate and tropical seas.
Habitat:
Floats at the sea surface.
Size:
40-80 mm long, as adults.
Diet:
Zooplankton and fish eggs, supplemented by symbiotic zooxanthellae.
Predators:
Pelagic snails and nudibranchs.
Useful Facts or Characters:
A clear, chitinous semicircular to triangular sail sticks up above the water with a blue float beneath made of concentric circles of gas-filled chambers. Small tentacles extend below the circular chambers. The sail is angled left or right.
Natural History:
Called the "by-the-wind sailor." Generally floats offshore but can be blown onshore in large numbers.
References:
Schuchert, P. (2010) The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 2. Revue Suisse de Zoologie 117: 337-555.
video source: http://www.youtube.com/watch?v=BTGxIXXt_VU
video source: https://youtu.be/ZJGO_bSsR3w