@glennmagusharvey here's a combo! Snails in the Juliidae family have evolved two-valved shells!
https://en.m.wikipedia.org/wiki/Juliidae
While there are bivalves that have evolved to have only one shell, like the tubular watering pot shell
http://www.realmonstrosities.com/2015/12/watering-pot-shell.html?m=1
Or no external shell at all, such as the bizarre "naked clam", which looks kinda like a slug!
https://nathistoc.bio.uci.edu/Molluscs/Chlamydoconcha%20orcutti/index.html
Evolution is stream always winding back in on itself!
Dangerous giant African snails in Florida spark quarantines
https://nypost.com/2022/07/01/dangerous-giant-african-snails-in-florida-sparks-quarantine/