The original paper gives the temperatures in Celsius:

For decades after their discovery, no eukaryote was shown to replicate above 60°C. We isolated a geothermal amoeba, Incendiamoeba cascadensis, that divides at 63°C and is motile up to 64°C. [...] The minimum growth temperature is 42°C, with no growth at 40°C or lower; optimal growth is at 55°C–57°C (Figure 2A; Table S6), and maximum growth is at 63°C, with no growth at 64°C or higher.