What is this ? :/

Hello everyone thankyou for taking the time to read my post.

So I currently have a small nano reef tank that includes:

Fish:
1 x yellow tang
2 x ocellaris clownfish
7 x chromis
1 x melanuras wrasse

Invertebrates:
1 x sand sifting starfish
4-5 x hermit crabs (orange/black/white dots on legs)
1 x turbo snail
4 x snails (unsure of type) :/

Corals
1 x leather toadstool
1 x hammer coral
? X mushrooms (far few different varieties in there)
1 x torch coral
1 x bubble tip anemone
1 x white anemone
7 x zoanthids (small colony came as hitchhikers)
1 x green gonipora
1 x green frogspawn coral
1 x plate coral
1 x purple/green Duncan's
1 x elegance coral
1 x green blastomussa
2 x scolymia
1 x colony of green star polyps

So today I found this small white egg looking thing floating in my tank and I can't seem to find anything about it on the internet. I was just wondering if any of you guys know what this is, I'm only new to the hobby and still have a lot of learning to do! Thanks again for taking your time to read.

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