Hmm cant identify

[andrews_james]

Any Clue what this is. Tank is about a year and a half old recently changed to better lighting and this thing just took off also found a 2nd one I never noticed before. Both are on/in a semi protected ledge. they are around 1 or more in size, the opening you see is about the size of a number 2 pencil eraser

 

[KJ]

Sponge.

 

[saltyfilmfolks]

Yup. A really cool one too.