The governing boards of the districts establishing the retirement plan shall provide for the administration of the funds and the payment of retirement salaries by a joint district retirement board composed of three persons not officers or employees of any of the districts, one representative of each district, one representative of the teachers of each district and one representative of the other employees of each district, who shall serve without compensation. The representatives chosen by the teachers and other employees shall be chosen by secret ballot. The county treasurer of the county in the county treasury of which the joint district retirement fund is created shall be ex officio a member of the joint district retirement board. All members of the retirement board shall serve for such terms as may be specified by the governing boards in establishing a plan. The joint district retirement board shall have such further powers and duties as may be prescribed by the governing boards of the districts.