A thing I found in my overflow, limpet?

[averagesteve]

I found these in my overflow, two of them roughly the size of a US quarter. I checked as many "hitch hiker id" threads and posts as I could and decided limpet? but I'm not sure as they don't seem to move or anything... I can't take a picture under more white light. I have t5s, sorry. To the naked eye they look almost white or semitransparent.

 

[ISpeakForTheSeas]

Sponges and spirorbid worms - harmless filter feeders. Cool growth pattern on the big sponge in your pics.

 

[averagesteve]

Sponges and spirorbid worms - harmless filter feeders. Cool growth pattern on the big sponge in your pics.

Thanks! I knew the spirorbid worms, but I didn't know what this sponge was. Limpets were the only thing that looked close. I have an internal corner overflow, so it's pretty large and a lot of things like to live in it, it's like having a whole little ecosystem in there.