What is this?

[louisianareef318]

This thing moves fast. 5 month old tank. What is it? Help!

 

[KrisReef]

Appears to be some kind of frilly nudibranch from your description and the picture?

 

[ISpeakForTheSeas]

Welcome to Reef2Reef!

Definitely a nudibranch - my first thought would be a Phyllodesmium species (they're coral-eaters), but pics under white light would help to say for sure.

Regardless, this one most likely isn't one you want in your tank (and you should probably check any corals you have for more/for eggs).

 

[louisianareef318]

I think Phyllodesmium nudibranch is it, you're right. We've been hunting and removing them. Ill get a little more aggresive. I'll try to remember to get a picture of one out of the tank. Thanks!

 

[louisianareef318]

By the way, these seem to eat GSP. They blend in nicely.