What did my frogspawn leave on the rock?

[Jake_the_reefer]

So my frogspawn when opened up covers the rock it sits on and it left a weird spot on the rock when It closed up for feeding. Any ideas what it is?

 

[Euphyllia97]

Could this be heads of the frogspawn?

 

[shred5]

Mesenterial filaments.. It looks like it might have been attacking the coral next to it.

 

[Glott3133]

Mesenterial filaments.. It looks like it might have been attacking the coral next to it.

Whatever that is, I like the diagnosis. My hammer has done the same thing on a rock that it sits on. I never knew what to call it, but I thought it made the rock look cool.