Amoeba, Paramecium, and Euglena all belong to the kingdom Protista.
The kingdom Protista is a diverse category that consists of microscopic organisms that do not fit into the other kingdoms of life such as Animalia, Plantae, or Fungi. Protists can be single-celled or simple multicellular organisms. They also vary widely in their methods of obtaining nutrients: some are photosynthetic like Euglena, which can produce its own food using sunlight, while others like Amoeba and Paramecium are heterotrophic, meaning they consume other organisms for nourishment.
This kingdom is an important group in biology as it showcases the diversity and evolutionary variations of lifeforms that exist in our environment, bridging the gap between the more complex multicellular organisms and the simpler single-celled entities.