Marine animals find all sorts of clever ways of moving about. Take this odd-looking creature for example. It has a flat disk and a stiff flap sticking out of its center. This is a Velella velella. Its flat body is filled with chambers of air. Velella make their way around by sitting on the ocean and use that flap to catch the wind and sail across the sea. No wonder they are also known as by-the-wind sailors.

Although it looks like some kind of jellyfish, Velella are actually a colony of individuals. Individual 'polyps' will take on different roles, like feeding the colony or reproducing. One thing super-cool about Velella is that the colonies are made up of either all male or all female polyps! 

They may look somewhat cute, but don't let that and their small size fool you. Velella are carnivorous critters, catching their prey in their long dangling tentacles which sport nematocysts - cells that fire little toxic barbs attached to a thread at unsuspecting animals. Us humans have little to fear though. Velella hunt for zooplankton, not people. Unless you happen to be allergic, their stings won't do you any harm. Still, if you did happen to come across a Velella (even a dead one), it's probably best not to touch it. If you can't resist poking a dead Velella (don't poke a live one - it's not nice for the Velella) or one ends up poking you, keep your hands away from your eyes and wash them thoroughly at the earliest opportunity.

Capturing tiny animals isn't the only food source for these amazing little sailors. 
Inside Velella lives microalgae called zooxanthellae. When the algae photosynthesis they produce energy that the Velella can 'feed' on as well as oxygen.