Members of Thermotoga are hyperthermophilic bacteria whose cell is wrapped in a unique sheath-like outer membrane, called a "toga".

The members of the phylum stain Gram-negative as they possess a thin peptidoglycan in between two lipid bilayers, albeit both peculiar.

The genome of Thermotoga maritima was sequenced in 1999, revealing several genes of archaeal origin, possibly allowing its thermophilic adaptation.

[2] The Neo-Latin feminine name "thermotoga" means "the hot outer garment", being a combination of the Greek noun θέρμη (therme, heat)[7] or more correctly the adjective θερμός, ή, όν (thermos, e, on, hot)[8] and the Latin feminine noun toga (the Roman outer garment).

[2] The precise relation of the Thermotogota to other phyla is debated (v. bacterial phyla): several studies have found it to be deep-branching (in Bergey's manual it appeared in fact in "Volume I: The Archaea and the deeply branching and phototrophic Bacteria"),[9] while other have found Firmicutes to be deep-branching with Thermotogota clustering away from the base.