Anyone have any idea what this is? I turned over this rock and found it. My bta was under for a while. Is it from the bta? It’s more on the pinkish side. Weird texture almost slick.
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ExactlyFrom your description I would guess this is a sponge. From the image, all I get is a weird substance.![]()

I turned on the brights. It’s thin like coraline.From your description I would guess this is a sponge. From the image, all I get is a weird substance.![]()
I was just using coraline as a comparison. This is about 4”x3” in size. It’s odd.Looks much thinner in the white light picture, and I still think it's probably a sponge? Coralline generally doesn't have that shiny glossy surface that a sponge often has, and coralline usually gets flakes or plates vs. sliming across a surface.
And the big clue is that this was growing on the underside before you turned the rock over. Criptic organism vs light seeking.
Thanks for following up. Very helpful information for future reference.Just wanted to update this older thread. The specimen is an encrusting sponge. No biggie until it irritates corals. It’s a good filter feeder.
I had 2 more mats pop up. Showed my guy at Tsm and he agreed it was a sponge. Thank you for your help!Thanks for following up. Very helpful information for future reference.Just wanted to update this older thread. The specimen is an encrusting sponge. No biggie until it irritates corals. It’s a good filter feeder.