Solvin Zankl / By-the-wind sailor (Velella velella) colony. Sargasso Sea, Bermuda.

Alex Mustard / Neustonic jellyfish (Porpita pacifica) at the surface, viewed from above. Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean.

Solvin Zankl / By-the-wind sailor (Velella velella) colony, Sargasso Sea, Bermuda.

Solvin Zankl / By-the-wind sailor (Velella velella) colony from underneath Sargasso Sea, Bermuda.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Jean E. Roche / Mass of By-the-wind sailor (Velella velella) jellyfish washed up on beach, Camargue, France, May.

Henley Spiers / Blue button (Porpita porpita) with a juvenile fish (most likely a species of jack) using it for shelter. Eastern Pacific, Costa Rica, February.

Sergio Hanquet / Blue dragon seaslug (Glaucus atlanticus) feeding on blue button (Porpita porpita), Tenerife, Canary Islands.

Sergio Hanquet / Blue dragon seaslug (Glaucus atlanticus) with Blue button hydroid colony (Porpita porpita) on which it feeds. Tenerife, Canary Islands. October

Sergio Hanquet / Blue dragon seaslug (Glaucus atlanticus) with blue button hydroid colony (Porpita porpita) on which it feeds. Tenerife, Canary Islands. October