phytoplankton

noun

Etymology: From phyto- + plankton. From Ancient Greek φυτόν (phutón, “plant”) + πλαγκτόν (planktón), neuter of πλαγκτός (planktós, “wandering”). However, they are no longer classified as plants, so the terminology is showing a historical meaning.

1. Plankton, especially those small in size, that obtain energy by photosynthesis.