1. Coccolithophores: These are single-celled algae that are covered in small, chalky plates called coccoliths. They are incredibly important in the ocean's carbon cycle, as they take up carbon dioxide and produce calcium carbonate. A well-known example is *Emiliania huxleyi*.

2. Cryptomonads: These are another type of single-celled algae, characterized by their unique shape and two flagella. They are also important in the ocean's food web, providing a food source for larger organisms. An example is *Cryptomonas ovata*.

3. Diatoms: While most diatoms are considered microplankton, some species are small enough to fit within the nanoplankton size range. These microscopic algae are encased in a glassy shell called a frustule and are responsible for a large portion of the world's oxygen production. An example is *Chaetoceros* sp.

It's important to note that the classification of plankton size is not always clear-cut. Some species can fluctuate in size depending on environmental factors, and some may overlap between different size categories.