What is this

[Orlando-Jeff]

Last night all my zoas and my birdsnest closed up for no apparent reason. Today I come home to find this on my zoas. All the zoas and birdsnest are on the same rock. Every thing else in the tank looks fine for now. getting ready to do a huge WC. All my parameters are good.
sal...1.025
cal...470
alk...9dkh
PH...8.1
temp 78
nitrate....05ppm

Don't want to lose my tank again

 

[Pat24601]

I am NOT an expert on this, but if you had just shown me the picture without the context, I thought it looked like vermetid snails. But, I've never had any on a coral like that and it doesn't really fit your background.

See what more knowledgable folks think.