👉 Monotremata is a term in biology that refers to a type of unicellular organism. These are single-celled organisms that have a cell wall and a cell membrane but no nucleus, mitochondria or chloroplasts. Monotremata include bacteria, yeasts, fungi, and protozoa. Bacteria, for example, are one of the most common types of unicellular organisms in nature. They can be found in soil, water, and even on the surface of plants.