These teeny-tiny little critters are, in a nutshell, the foundation of the food chain for the ocean world. Without them, there would not be much to see in the ocean even though you can't see them yourself.
They are more than just food though, they also are huge carbon dioxide absorbers accounting for about a third of all produced by us dirty humans. Pretty impressive. They live in the upper layers of the ocean where they produce organic compounds via photosynthesis. They actually account for half of all photosynthesis done on the planet. Even more impressive!
Their name comes from the Greek words meaning python (plant) and planktos (drifter/wanderer). Depending on which particular strand of phytoplankton is present, it changes the colour of the water. Here in Koh tao we get a green tint. If there is enough of them, you can even see them from space! Super impresive!!
These guys were captured off the coast of ireland by NASA's Terra satellite