They are simple eukaryotic organisms that are neither fungi, plants, and animals.
Protista is unicellular in nature but can also be found as a bulk of cells.
Protista organisms are considered as the first eukaryotic types of life and a predecessor to fungi, plants, and animals.
Those organisms that are single-celled, consume food, and swim in the water are generally called Protozoa. They belong to the kingdom called Protista and are classified into different phyla based on how they move.