In taxonomy, the Thermoplasmata are a class of the Euryarchaeota. All are acidophiles, growing optimally at pH below 2. Picrophilus is currently the most acidophilic of all known organisms growing at a minimum pH of 0.06. Many of these organisms do not contain a cell wall, although this is not true in the case of Picrophilus. Most members of Thermotoplasmata are thermophilic.