Above is a velella (related to the jellyfish and corals). Velellas float in the ocean water, eating plankton. They have tiny tentacles which release poison, helping them catch their prey. The tentacles are able to pierce through human skin, however, we are immune to their toxins.
Velellas are about 7 cm long and with the help of the wind they use their ‘wing’ (at the top) to navigate them over the surface of the ocean. If wind conditions are unfavourable, they may be stuck on the beaches by the thousands as they have no means of locomotion apart from their ‘wing’.