Animalcula is a term that refers to microscopic organisms that are commonly found in water and soil. These tiny creatures are hard to see with the naked eye, and there are many synonyms that can be used to describe them. Some of the most commonly used synonyms for animalcula include microorganism, protozoa, bacterium, fungus, and virus. Each of these words refers to different types of microscopic organisms that play unique roles in the ecosystem. Microorganisms are important because they help to break down organic materials and recycle nutrients. Protozoa are single-celled organisms that can be either free-living or parasitic. Bacteria are diverse group of organisms that are found in many different environments, and play important roles in everything from digestion to disease. Fungi are important decomposers in the ecosystem, and viruses are tiny infectious agents that can cause a wide range of diseases.