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