Mo. Rev. Stat. § 306.075
A "motorized amphibious vehicle" is a self-propelled vehicle designed or used for transporting property or eight or more persons on the highways and waters of this state. A motorized amphibious vehicle shall not be considered a motor vehicle for the purpose of titling and registration as defined in chapter 301 and shall not be considered a commercial motor vehicle as defined in section 302.700. A motorized amphibious vehicle shall be treated as a vessel as defined in this chapter for the purposes of titling and registration and shall be subject to all provisions of this chapter. Such vehicles are to be treated as a motor vehicle only for the purposes of complying with the provisions of sections* 302.010 to 302.605 and chapters 303, 304, 307 and 577 while the vehicle is being operated on the highways of this state. Every operator of a motorized amphibious vehicle shall hold a valid license to operate a motor vehicle when operating the vehicle on the highways of this state and is subject to any licensing requirements of the United States Coast Guard and the provisions of this chapter when operating such vehicle on the waters of this state.
§ 306.075, RSMo
Effective 7/27/1989