This section applies to the following types of entities: A member of a national securities exchange who transacts a business in securities directly with others than members of a national securities exchange; a broker or dealer who transacts a business in securities through the medium of a member of a national securities exchange; a broker or dealer, including an OTC derivatives dealer as that term is defined in § 240.3b-12 , registered pursuant to section 15 of the Act (15 U.S.C. 78 o); a security-based