Sticks for variable length (0.17 to 0.35 x 1-100 microns), not moving, sometimes connected with the presence of terminal and lateral spherical protrusions, and at each end of pili. Gram negative. Anaerobes. Growth of yeast extract or sulfur bactotryptone Breathing (sulfo-reduction).Thermoacidophiles, optimum temperature 85-90 ° C (68 -100 ° C), optimum pH 5-6 (2.8 to 6.7), time division 10 h. Occur in solfatars land. DNA contains 57 mol% G+ C. Two species,Thermofilum pendens .
