I was overlooking my LR in my refugium and found this, it may not be anything but, it doesn't hurt to find out if it is anything or if I should take it out or move it to the main tank.
I would agree on the sponge guess. Kind of hard to tell for sure. Most of my sponges are in low light and low flow areas. Sponges are great natural water filters.
its a ball sponge, cinachyra, they are not too harmfull, the worst thing is that they can overgrow things in the tank and choke them out. they filter out small particulate matter, mostly bacterial aggregates found in the water.