What are these squiggly lines on zoas?

[ItsAName]

I'm assuming it's part of the anatomy, but I'm not sure. If it is part of the anatomy, what is it, and what do they do?

Close up



Example of them on all the zoas



It was easier to take pictures and show it with the lights off and a flashlight. That is why they are closed. The Zoas are healthy (as far as I know haha)

 

[nautical_nathaniel]

I believe it's like their internal structure, it contracts as they close up or something.