What is this

[WillT84]

Does anyone know what this is I just found a few of them in my sump and 1 or 2 in my aquarium

 

[X-37B]

Montiora eating nudibranch.
Their is never one.

 

[JGT]

Hard to tell size but looks a bit too big for a MEN, but could be. Def a nudi tho.

 

[MAH]

Does it move?

 

[ISpeakForTheSeas]

That looks like a sponge to me, so I second the "does it move?" question.