Mo. Rev. Stat. § 104.095
If an employee with ten or more years of creditable service dies before retirement, his spouse, if named as his beneficiary, may elect, in lieu of the benefits provided in section 104.140, to receive the reduced survivorship benefits under this section calculated as if the member had retired as of the date of his death. If a member who is entitled to a deferred normal annuity under the provisions of section 104.035 dies before retirement, his spouse, if named as his beneficiary, shall receive the reduced survivorship benefits under section 104.090 calculated as if the member had retired as of the date of his death.
(L. 1988 H.B. 1643 & 1399)