I had vermetid snails, the really really large ones, in my tank and their slime-nets looked nothing like what is shown in those pictures. The whole way those nets over those corals look like - precisely like those unruly spider webs you see covering bushes in the fall - doesn't fit vermetid snails.
You might want to check Google scholar if there are articles about something that fits these nets. I found that there are lots of studies done on coral pests and diseases. The only tricky thing with Google scholar is to pick the right key words to find what you are looking for.
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