What is this frilly thing?

[DmitryB]

I've seen this on my glass a few times, no idea what this frilly thing is. Is this a creature or the remains of a creature?

 

[Mr_Knightley]

Do you have Cerith snails? This is what it looks like when my ceriths lay eggs.

 

[DmitryB]

Do you have Cerith snails? This is what it looks like when my ceriths lay eggs.

I do, yes!

 

[Mr_Knightley]

I do, yes!

Then they're more than likely Cerith eggs! Fish or crabs will most likely eat them before they hatch, and the babies are pelagic so it's not feasible to raise them, but it's a good sign that you have a healthy tank :)