Sponge or egg sack?

[fishybizzness]

I just found this on my rocks. Any ideas of what it may be?

 

[KJ]

Sponge.

 

[Greybeard]

Yup. Sponge. I'm no biologist, but I'm unaware of any reef dwelling critter that uses a spider-type egg sack. Even sea spiders don't use such a structure.

 

[fishybizzness]

Next question, good or bad?

 

[Greybeard]

Sponges are natural filters. An excellent thing to have in your reef.

 

[Greybeard]

If you decide you want to get rid of it, not that I'd see a reason to do so, but you could pick up a tiger cowrie. Your sponges would be gone in no time.

 

[fishybizzness]

I started doing water changes with nsw about 2 months ago. It must have come in in the water. The tank has been set up for almost 1 year and I never saw any sponges before this.

 

[fishybizzness]

I think I'll keep it! I always love seeing new things pop up in my tank. For me, that helps keep it interesting!