What is this magnificent beast?!?!?

[Dr4gula.f32]

It's about 2.5 inches across. The lower half of the shell has a pearl iridescent color to it, while the top is, umm, less appealing. Petco had it for 5 bucks. I couldn't walk away without it.

What is it?

 

[WheatToast]

https://www.reef2reef.com/threads/la-plata-petco-has-crown-snails.925589/
I've heard Petco sometimes offers Megastraea undosa (once Astraea undosa) (wavy turban snail or top crown snail) which might be what you're seeing. These are also offered by Blue Zoo Aquatics. Here's one I found near Los Angeles in the surf with more growth on it:

 

[Dr4gula.f32]

I think you're correct. I was googling giant turban snail and wavy turban snail came up in the results. I didn't see any pearlescent shells though. But this is by far the closest match I've seen.

I assume it's reef safe?

 

[Lbrdsoxfan]

IME they are reef safe, seen them in a few tanks but they can be wrecking balls to frags and non secured rock due to the sheer size.

 

[Reefer Reboot]

Native to southern California, they are more of a temperate (cool) water species. They feed mostly on kelp. So don't be too surprised if it doesn't last all that long.

 

[WheatToast]

I think you're correct. I was googling giant turban snail and wavy turban snail came up in the results. I didn't see any pearlescent shells though. But this is by far the closest match I've seen.

Here's one with a pearlescent shell being overtaken by coralline algae:
https://commons.wikimedia.org/wiki/File:Astraea_undosa.jpg

I assume it's reef safe?

From what I’m reading online, their maximum preferred temperature is around 75°F.
Diet: https://bioone.org/journals/pacific...straea-undosa-Gastropoda/10.2984/71.4.9.short

 

[TangerineSpeedo]

I happen to have two in my temperate tanks. They can get to the size of a six inch softball. Yes, they are bulldozers. If bothered by another snail or hermit, they will do a rapid twisting of their shell, kinda like a buzzsaw. If a smaller hermit or Turban climbs aboard it is just like an 8 sec bull ride, LOL.
Feeding wise they seem to like the aforementioned Kelp, but will also be satisfied with glass algae etc. I don't think they would ever touch dried kelp. But you can always go to the Japanese market and get some fresh kelp, if you don't live two blocks from the ocean. They are from temperate waters, but it seems that snails/slugs have a much wider tolerance, but I would expect a shorter life.