Mo. Rev. Stat. § 104.395
1. In lieu of the normal annuity otherwise payable to a member pursuant to sections 104.335, 104.370, 104.371, 104.374, or 104.400, and prior to the last business day of the month before the annuity starting date pursuant to section 104.401, a member shall elect whether or not to have such member's normal annuity reduced as provided by the options set forth in this section; provided that if such election has not been made within such time, annuity payments due beginning on and after such annuity starting date shall be made the month following the receipt by the system of such election, and further provided, that if such person dies after such annuity starting date but before making such election, no benefits shall be paid except as required pursuant to section 104.420:
Option 1. An actuarial reduction approved by the board of the member's annuity in reduced monthly payments for life during retirement with the provision that upon the member's death the reduced annuity at the date of the member's death shall be continued throughout the life of, and be paid to, the member's spouse to whom the member was married at the date of retirement and who was nominated by the member to receive such payments in the member's application for retirement or as otherwise provided pursuant to subsection 5 of this section. Such annuity shall be reduced in the same manner as an annuity under option 2 as in effect immediately prior to August 28, 1997. The surviving spouse shall designate a beneficiary to receive any final monthly payment due after the death of the surviving spouse; or
Option 2. The member's normal annuity in regular monthly payments for life during the member's retirement with the provision that upon the member's death a survivor's benefit equal to one-half the member's annuity at the date of the member's death shall be paid to the member's spouse to whom the member was married at the date of retirement and who was nominated by the member to receive such payments in the member's application for retirement or as otherwise provided pursuant to subsection 5 of this section, in regular monthly payments for life. The surviving spouse shall designate a beneficiary to receive any final monthly payment due after the death of the surviving spouse; or
Option 3. An actuarial reduction approved by the board of the member's normal annuity in reduced monthly payments for the member's life with the provision that if the member dies prior to the member having received one hundred twenty monthly payments of the member's reduced annuity, the member's reduced annuity to which the member would have been entitled had the member lived shall be paid for the remainder of the one hundred twenty months' period to such person as the member shall have nominated by written designation duly executed and filed with the board. If there is no such beneficiary surviving the retirant, the reserve for such annuity for the remainder of such one hundred twenty months' period shall be paid as provided under subsection 3 of section 104.620. If such beneficiary dies after the member's date of death but before having received the remainder of the one hundred twenty monthly payments of the retiree's reduced annuity, the reserve for such annuity for the remainder of such one hundred twenty-month period shall be paid as provided under subsection 3 of section 104.620; or
Option 4. An actuarial reduction approved by the board of the member's normal annuity in reduced monthly payments for the member's life with the provision that if the member dies prior to the member having received sixty monthly payments of the member's reduced annuity, the member's reduced annuity to which the member would have been entitled had the member lived shall be paid for the remainder of the sixty months' period to such person as the member shall have nominated by written designation duly executed and filed with the board. If there be no such beneficiary surviving the retirant, the reserve for such annuity for the remainder of such sixty months' period shall be paid as provided under subsection 3 of section 104.620. If such beneficiary dies after the member's date of death but before having received the remainder of the sixty monthly payments of the retiree's reduced annuity, the reserve for such annuity for the remainder of the sixty-month period shall be paid as provided under subsection 3 of section 104.620.
5. Effective July 1, 2000, a member may make an election under option 1 or 2 after the date retirement benefits are initiated if the member makes such election within one year from the date of marriage or July 1, 2000, whichever is later, under any of the following circumstances:
(L. 1967 p. 191, A.L. 1972 S.B. 548, A.L. 1981 H.B. 835, et al., A.L. 1984 H.B. 1370, A.L. 1986 H.B. 1496, A.L. 1988 H.B. 1643 & 1399, A.L. 1994 H.B. 1149, A.L. 1995 H.B. 416, et al., A.L. 1997 H.B. 356, A.L. 1999 S.B. 308 & 314, A.L. 2000 H.B. 1808, A.L. 2001 S.B. 371, A.L. 2007 S.B. 406)