chondrophore

This is the velella, a small free floating hydrozoan. It’s currently the only known species in the genus.
Velella is a cosmopolitan genus of free-floating hydrozoans that live on the surface of the open ocean. There is only one known species, Velella velella, in the genus. Wikipedia
Scientific name: Velella velella
Higher classification: Chondrophore
Rank: Genus