Microsporidia

Microsporidia is a group of unicellular, spore forming parasites classified within or alongside the fungal kingdom based on genetic evidence, despite lacking many structures typical of fungi and having long been studied instead as protozoan parasites. Microsporidia are obligate intracellular parasites of animals, infecting hosts ranging from insects and fish to humans, and their spores contain a uniquely coiled polar tube used to inject infectious material directly into a host cell, a mechanism unlike anything found elsewhere among fungi.