While vacationing off the coast of Wales, I've been seeing a lot of jellyfish. In addition to the common moon jellyfish, there have also been large numbers of Blue Lion's Mane (Cyanea lamarckii), Barrel jellyfish (Rhizostoma octopus) and By-the-wind Sailors (Velella velella).
Cyanea lamarckii - Abersoch, Wales
Moon jellyfish and Blue Lion's Mane are not uncommon species, but this is the first time that I have seen By-the-wind Sailors. What surprised me the most is the size - the descriptions say that they grow up to 10 cm, but almost all that I saw were 1cm at best, although there were many of them. Occasionally I would see a larger one, but no longer than 2cm at most.
Velella velella - Harlech, Wales
There were large numbers of Barrel jellyfish close to the shores of Cardigan Bay - I counted almost 20 in three days, all but three of which were washed up on shore. They aren't supposed to be coming this close to the beach, but apparently these mass sightings do happen when the weather is unusually warm. The picture below was taken from the edge of the marina in Barmouth. Hopefully he managed to escape to deeper water before the tide retreated.