Is there a way I can be on my husband's insurance and retirement?

I've been married 16 years Jan 9- I was not on my husband's insurance and we learned that it was only a one time "offer" to sign up for his insurance, and retirement. So is this really a fact? Is there no way I can get on his insurance and retirement-and of course he will get my pension/half of when I retire. What can be done? Anything? 16 years seems like a long time to be married and not be looked at as his wife in the name of insurance and retirement.