Symbiotic relationships, where different species live in close association, are found across various biological kingdoms. Cnidarians, such as corals, often host symbiotic algae (zooxanthellae) that provide them with nutrients. Fungi exhibit numerous symbiotic relationships, notably mycorrhizae with plant roots and lichens formed with algae or cyanobacteria. Protozoa also engage in symbiosis; for example, many protozoa live symbiotically within the digestive tracts of other animals, aiding in digestion.