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 21 online stores.
33% Limited Liability Company (LLC) (7 sites)
19% Public limited Company (INC. / Corporation) (4 sites)
19% Private Limited Company (LTD) (4 sites)
19% Sole Proprietorship (4 sites)
10% other (2 sites)