A circular ring of DNA that typically exists in bacteria and that codes for certain traits is known as a/n

Answer is  Plasmid.

A plasmid is a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA. Plasmids naturally exist in bacterial cells, and they also occur in some eukaryotes. Often, the genes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance.

answer; cnidarians;