The family Hepadnaviridae contains Hepatitis B viruses that are enveloped viruses with reverse-transcribed DNA genomes.
However, recently scientists reported the discovery of a diversified family of fish viruses, designated Nackednaviruses, which lack the envelope protein gene, but otherwise exhibit key characteristics of Hepatitis B viruses, including genome replication via protein-primed reverse-transcription and utilization of structurally related capsids.
Their envelope protein gene emerged de novo, leading to a major transition in viral lifestyle, followed by co-evolution with their hosts over geologic eras.
The scientists identified Hepatitis B-related viruses by homology searching in public sequence databases at the National Center for Biotechnology Information (NCBI). What they found were three new Hepatitis B-like viruses: African Cichlid Nackednavirus (ACNDV), Rockfish Nackednavirus (RNDV) and Sockeye Salmon Nackednavirus (SSNDV).
 Lauber et al: Deciphering the Origin and Evolution of Hepatitis B Viruses by Means of a Family of Non-enveloped Fish Viruses in Cell Host & Microbe – 2017. See here.