Haloplasmataceae is a family within the order Haloplasmatales, which currently includes one single genus and species: Haloplasma contractile. This family has unusual phenotypic features –the most noticeable being a unique morphology and cellular contractility cycle– and a distinct phylogenetic position between the Firmicutes and the Tenericutes (Mollicutes). Members of the Haloplasmataceae have been isolated from the upper sediments of a deep-sea anoxic brine in the Red Sea, but cultivation-independent studies have found related sequences in a wide range of biotopes including other extreme environments, con- taminated soils and marine sediments, as well as intestinal samples. The isolation and description of new representatives of this family might therefore result in significant changes to the current description.