Ramazzottius varieornatus is a species of ciliates in the genus Ramazzottius. It is found in hot springs and other habitats with high temperatures and salt concentrations. It is an obligate thermophile, meaning that it cannot grow at temperatures below 40°C. R. varieornatus has a unique life cycle, alternating between two forms: an infectious cyst and a motile trophozoite stage. The cysts are resistant to extreme conditions and can survive for long periods of time without food or water. When they come into contact with suitable hosts (such as amoebae), the cysts germinate and release trophozoites, which invade the host cells and replicate inside them. After replicating for some time, the trophozoites transform back into cysts and are shed from the host cell. This cycle can repeat itself many times, with each new generation of cysts being more resistant to environmental stresses than the last.
R. varieornatus was first described in 1988 by Italian microbiologist Giuseppe Ramazzotti. It is one of only a few known species of ciliates that can withstand such high temperatures and salt concentrations; others include Acineta thermarum and Spirostomum thermarum. R. varieornatus is thought to be native to Italy, but it has also been found in hot springs in Hungary, Iceland, Japan, Romania, Russia, Slovenia, Spain, Switzerland, Turkey, and the United States