Need Help Identifying Something

[Truckie]

Was wondering if someone could help me ID these things that have been popping up in my tank. I noticed this one on the live rock a few weeks ago and today I found a few more. Looks like some kind of egg casing to me but I have no idea what it's from.

55 Gal. with:
-2 Clownfish
-Royal Gramma
-Yellow Watchman Goby
-Pistol Shrimp
-2 Emerald Crabs
-Approx 6 hermit crabs
-Approx 6 snails (I noticed one or two died recently)

Tank has been running since April

 

[Aquarian]

It's a empty (dead) bivalve or clam shell, I'm sure you a few live ones in there too. They are good to have in your tank.

 

[ErinCahir]

+1 aquarian.