A newly discovered amoeba species, named Incendiamoeba cascadensis, has been found living in hot spring water as warm as 63°C (145°F) in California's Lassen Volcanic National Park. The findings, published in the journal Cell, reveal that this amoeba can survive temperatures up to 70°C (158°F) by altering its shape and forming a protective outer layer. This discovery challenges the long-held belief that 60°C (140°F) is the upper temperature limit for eukaryotes—organisms with complex cells, including animals, plants, fungi, and some microbes. The study, which took place between 2023 and 2025, involved collecting samples from geothermal streams in Lassen Volcanic National Park, where water temperatures ranged from about 47°C to 64°C (117°F to 147°F). Researchers observed that Incendiamoeba cascadensis can perform mitosis—the process by which eukaryotic cells divide—at 63°C (145°F). This confirms that the amoeba not only survives but also thrives in conditions previously thought too extreme for eukaryotes. The study also uncovered unique genetic traits that may help the amoeba withstand high temperatures. It possesses additional genes related to protein maintenance and DNA repair, which are not found in other amoebae that live in cooler environments. Moreover, its proteins have more positively charged amino acids on their surfaces, a feature also seen in some of the most heat-tolerant bacteria and archaea. These characteristics may help stabilize proteins and prevent them from breaking down in extreme heat. The discovery of Incendiamoeba cascadensis could influence future research on how organisms tolerate extreme environments, by removing assumptions about temperature limits. Currently, the record for the hottest-growing organism belongs to Methanopyrus kandleri, an archaeon that lives in hydrothermal vents in the deep ocean at temperatures up to 122°C (252°F). However, this new amoeba is the first known eukaryote to thrive at such high temperatures, opening new possibilities for understanding life's adaptability in extreme conditions.