To the limits of where our understanding of how "entities" are connected to one another (homology). Yes, there's nothing like them. You could make an argument they are "viroid-like" and there's a deeper evolutionary connection between viroids/viruses/plasmids, but the information theory to formally establish such a connection is not sufficiently developed. It's a worthy scientific problem!
Is it common to find new viruses/viroids/biological agents? Well it certainly is starting to feel that way to me.
Is it common to find new viruses/viroids/biological agents? Well it certainly is starting to feel that way to me.