Ok I’m stumped

[Reefing_addiction]

This wasn’t in my tank the other day. At least I haven’t noticed it till today.
Found it in my sand bed. White side up

 

[Crabs McJones]

It's a snails operculum. The little "trap door" when they retreat into their shell. Must have had a snail die recently.

 

[reefwiser]

A snail

 

[TriggerFinger]

Definitely a snail and the shimmery brown part is the operculum. It looks like it’s kinda flat?

 

[FLReefer101]

It’s a snail

 

[vetteguy53081]

This is a whorl shell likely occupied due to shape, by a sea butterfly, classified as a pteropod mollusk.

 

[Soren]

I can confirm that it is a snail operculum, or trapdoor covering, more specifically like mine from dead turbo snails. I was stumped as well when I first found one in my tank, then another, then a third. There are about 6-8 large empty turbo snail shells in my tank left from the previous owner, and I see the same operculum on my living turbo snail.

Here is a link to a video from someone else with a Mexican turbo snail showing the operculum like yours.

 

[Reefing_addiction]

Ok so I had a large turbo (turban) snail die. and can I say OMG that was the worst smelling thing ever!!!!! Pulled it out and rinsed until I got all the slimy stinky pieces out and threw the shell back in

thank y’all!

 

[TriggerFinger]

Wow! That’s all an operculum...I’ve never seen my large turbos show theirs. Amazing!!