I no longer live in Florida but he does. After not paying for 16 years ( for two children ) Isn't this considered a felony? What can I do. I still have a case number with the Clerk of Court. Can he be arrested?

Have you taken him back to court to enforce your order.
Have you ever turned him over to child support enforcement?

If the original case was in Florida and he still lives there than Florida has jurisdiction.

Florida law does criminalize non payment. But that is an extreme step. Have you contacted the Florida Child Support Enforcement Agency? This site has info for you on doing so. Florida Child Support, look no further

Without knowing what you have done over the past 16 years to collect support its hard to advise further.

I don't know the laws of your State.. but in my State he would OWE all the money!
And, you can still file on him.