Velella Velella or By- The- WInd- Sailor
I spotted this on a beach in South West Scotland. It is known by the two names above. I spent ages looking at it on the beach - I'd never seen anything like it before and couldn't really fathom out what it was. It was the most beautiful shade of midnight blue. The Marine Conservation Society says of them - "Not strictly a jellyfish but a similar marine animal called a hydranth. Blue-purple, up to 10cm long with an upright 'sail'. Usually found in vast swarms."