I don't see a barnacle, but I would advise you to rasp the shells of all snails and hermits with a brush before putting into your tank. I have gone as far as carefully using hydrogen peroxide on the shell to kill potential bad hitchhikers. Not cleaning shells increases the probability of introducing various unwanted hydroids, algaes, worms, et cetera.
The "chungus" ( idfk.. lol) infested snail can go duke it out with the hitch hiking bristle worm in a separate tank. Idk exactly what will develop from the odd little life on the shell but if it develops into something else substantial, I'll update. Take care and thank you for your time and assistance.