<Li> Acidophiles, optimum growth pH of less than 3, including the genera Sulfolobus and Picrophilus . </Li> <Li> Piezophiles, (also known as barophiles), prefer high pressure up to 130 MPa, such as deep ocean environments, including the genera Methanococcus and Pyrococcus . </Li> <Li> Halophiles, grow optimally in high salt concentrations between 0.2 M and 5.2 M NaCl, including the genera Haloarcula, Haloferax, Halococcus . </Li> <P> Methanogens are a significant subset of archaea and include many extremophiles, but are also ubiquitous in wetland environments as well as the ruminant and hindgut of animals . This process utilizes hydrogen to reduce carbon dioxide into methane, releasing energy into the usable form of adenosine triphosphate . They are the only known organisms capable of producing methane . Under stressful environmental conditions that cause DNA damage, archaeal cells of some species aggregate and transfer DNA between cells . The function of this transfer appears to be to replace damaged DNA sequence information in the recipient cell by undamaged sequence information from the donor cell . </P>

How do unicellular protists carry out all necessary biological functions without having organs