Endospores form inside the original bacterial cell, as described above. Exospores form outside by growing or budding out from one end of the cell. Exospores also don't have all the same building blocks as endospores, but they're similarly durable. Cysts are thick-walled structures that, like spores, protect bacteria from harm, but they're somewhat less durable than endospores and exospores. Bacteria aren't the only microbes that can form protective spores, however.
Some protists can, too.
Microsporidia are found mainly in the guts of insects and the skin and muscles of fish, although a few species can cause illness in people. Microsporidium spore with tube thrust into host cells Courtesy of CDC Microsporidia spores are usually round, oval or rod-shaped, although many species have elaborately shaped spores that may help hide them from their host immune systems. The spores help the protozoa survive while outside of a host's body. Typically, hosts are infected when they swallow Microsporidia spores. Once the spores reach the gut, they poke a tube through their spore coats.