A side view, a bird’s eye view and a fish’s eye view of the ‘by the wind sailor’. Click on the image to open a larger version. Copyright: Richard Kirby.
Looking very much like a tropical island, the central image is a bird’s eye view, looking down upon Velella velella, the by the wind sailor, a jellyfish that invented sailing long before humans evolved, let alone took to the seas.
Living its adult life floating on the ocean’s surface, the by-the-wind sailor is a member of the pleuston, the small community of animals that live half in and half out of the water. Projecting vertically above the flat oval disk is a stiff vane made of chitin – the same material as an insect’s cuticle – that acts like a small sail. Around the base of the sail are a series of concentric air-filled tubes that provide buoyancy.
The bottom image is how a fish might see Velella. Dangling in the water beneath the oval disc are the jellyfish’s feeding tentacles surrounding its central mouth. As the wind propels the animal across the ocean’s surface these tentacles bearing harpoon-like stinging cells catch small zoolplankton and fish larvae upon which the jellyfish feeds. This is not the only source of food for Velella velella however, since the golden-brown colour in the tissues reveals the presence of zooxanthellae –symbiotic photosynthetic microalgae – that provide the jellyfish with an additional source of organic carbon.
Dr Richard Kirby is a University Research Fellow and is demonstrating his work at the Summer Science Exhibition 2011.