Giant virus
A giant virus is a very large virus. They are sometimes called a girus. Some of them are larger than typical bacteria. All known giant viruses belong to the phylum Nucleocytoviricota.
The genomes of many giant viruses code for unusual genes which are not found in other viruses. These include genes involved in glycolysis and the TCA cycle, fermentation, and the cytoskeleton.
The first giant viruses to be described were discovered in 1981.
Note, in the illustration from an electron microscope, the virus is surrounded by a thick (~100 nm) layer of filamentous protein fibres.
Origin
There are two main hypotheses. Either they evolved from small viruses by picking up DNA from host organisms; or they evolved from very complicated organisms by genome reduction.
References
Viruses