There are several forms of legal entity that can be used to run a merchant site.
Below, you will find a small study based on a sample of 18 online stores.
33% Limited Liability Company (LLC) (6 sites)
22% Public limited Company (INC. / Corporation) (4 sites)
22% Sole Proprietorship (4 sites)
11% other (2 sites)
11% Private Limited Company (LTD) (2 sites)