[2] Additional common features include a rod-like structure, an RNA-binding "delta antigen" encoded in the genome, and animal hosts.

Most lineages of this realm are poorly understood, the notable exception being the genus Deltavirus, comprising the causal agents of hepatitis D in humans.

It has been proposed that they may have derived from retrozymes (a family of retrotransposons) or a viroid-like element (i.e. viroids and satellites) with capsid protein capture.

[4][5] The first taxa of this realm to receive acceptance by the ICTV is the species Hepatitis delta virus and its genus Deltavirus, in 1993.

In 2020, Hepatitis delta virus was abolished and replaced with eight new species, and the taxonomy developed to reach its current form, detailed below.