Mo. Rev. Stat. § 77.070

At the first regular meeting of the city council after the election in each year--which meeting shall occur at the time fixed by ordinance, but shall not be later than the fourth Tuesday in April--the council shall elect one of its members president pro tem, who shall hold his office for the term of one year, and who, in the absence of the mayor, shall preside at the meetings of the council; provided, that in the absence of the mayor and president pro tem the council may select one of its members present to preside at such meetings, who shall be styled "acting president pro tem".