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 11 online stores.
27% Public limited Company (INC. / Corporation) (3 sites)
27% Limited Liability Company (LLC) (3 sites)
18% other (2 sites)
18% Sole Proprietorship (2 sites)
9% Private Limited Company (LTD) (1 sites)