What is this?

[Isopod80]

Hmm, I was ready to stand corrected and concede to @Isopod80 , but after looking a little closer, it may be neither of these. OP's snail has white dot surrounded by pigmented mantel.

Search Diminovula margarita. The patterning can be variable. It could be another variety of Diminovula as well.

 

[WheatToast]

Ok, i found the i.d. Diminovula margarita. (Margarita egg cowrie) a variety of false cowrie. Unfortunately, it feeds on soft corals. Too bad, the things are awesome looking.

That’s a shame . It’s such a beautiful organism!

 

[Isopod80]

This may be more like it Diminovula concinna

 

[Isopod80]

It's hard to get an exact species i.d. without a close up shot. It definitely appears to be a Diminovula sp. false cowrie of some kind.