Pelagia - Fearsome Jellyfish
Mauve jellies move in droves, their nasty stings feared by swimmers.

Velella - Planktonic Vessels
Colonies of polyps transported by prevailing winds, velella drift at the surface of warm seas.

Illustration in synthesized images of the seasons of the ocean: a year from the Arctic - Animation Clement Fontana

Siphonophores - The longest animals on the planet
Cousins of corals, siphonophores are colonies of specialized individuals called zoids. Some catch and digest their prey, others swim, or lay eggs or sperm.

The seasonal evolution of the chlorophyll a concentration as seen by a « water color » satellite (SeaWifs) in the Atlantic Ocean.

Les Dinoflagellés - Ceratium hexacanthum
chaîne de Ceratium hexacanthum qui restent les uns à la suites des autres au fur et à mesure des divisions.
Le mouvement des flagelles est bien visible.