it look like a gooey egg mas of some sort.....what type of snails do you kep in the tank? never heard of one big like that, or that was mobile.....does it react to stimuli at all?
very weird!
good luck
jon
its not attacking anything. It is from your six line wrasse. I have had the same situation a couple of times in my tank but it will disappear or something will consume it. Get you flash light out around 2 am tonight and go looking for the wrasse. It will be wrapped in the same thing.
I completely agree with what others have said, it's from the mucus of the sixline wrasse. Often times, as others have said, the wrasse will wrap itself around the mucus and bury itself in the sandbed during the night. It's quite normal and there's nothing to be worried about
Take Care,
Graham