Fungi (singular fungus) are creatures belonging to kingdom Fungi (like mushrooms, molds and yeasts) or extraterrestrial creatures similar to fungi in nature and lifestyle. Fungi are usually heterotrophs and absorb food from the environment. They may take the role of decomposers, mutualistic symbionts, parasites or even predators of tiny worms. Fungal organisms are difficult to classify as either fauna or flora, though they have been included among flora by some authors. Genetically, Earth fungi are more closely related to Earth animals than to Earth plants. Additionally, some fungi are microscopic in size, and thus can be classified as microorganisms.