We previously reported the isolation of five strains of a thermophilic gliding organism. These strains are described here as a new genus and species, Thermonema lapsum. The isolates can be readily distinguished from other thermophilic gliding bacteria as they are apparently unicellular aerobic filaments that grow optimally at 60°C. Their cell walls are similar in ultrastructure to those of gram-negative cells, but they are susceptible to penicillin G. Our isolates can be grown on a fully defined medium containing amino acids. Oxidation-versus-fermentation tests indicate that deamination takes place. The type strain, strain 23/9, has been deposited with the American Type Culture Collection as strain ATCC 43542.