I've never heard of a retirement tax shelter (IRA, etc.) that is held as joint tenants. You own your plan; your spouse appears on it as a beneficiary - and vice versa.

It is true that your spouse must be included as a beneficiary - or else must "sign off" by waiver of spousal rights. (These are issues that often are settled as part of a divorce decree - or sometimes as part of a pre-nuptial agreement.)