Based on the given description, the "thing" you discovered, which has only RNA as a nucleic acid and lacks both a membrane and cytoplasm, is most likely a virus. Viruses are infectious agents that are composed of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. They do not possess cellular structures like membranes or cytoplasm. Viruses are obligate intracellular parasites that require host cells to replicate and carry out their life cycle.