Plankton is a diverse group of organisms that drift in water, including:

* Phytoplankton: Microscopic algae that are the base of the food chain in many aquatic ecosystems.

* Zooplankton: Tiny animals like copepods, krill, and jellyfish that feed on phytoplankton and other zooplankton.

So, planktivores eat things like:

* Algae

* Copepods

* Krill

* Jellyfish

* Small crustaceans

Examples of planktivores include:

* Whales: Humpback whales, blue whales, and minke whales are all planktivores that use baleen plates to filter plankton from the water.

* Fish: Herring, sardines, anchovies, and some types of tuna are planktivorous fish.

* Birds: Some seabirds, like penguins and albatrosses, feed on plankton.

* Insects: Some aquatic insects, like mosquito larvae, are planktivores.

It's important to note that planktivores can be filter feeders or active hunters. Filter feeders, like baleen whales, strain plankton from the water. Active hunters, like some fish, actively chase and capture individual plankton organisms.