<a href=showthread.php?s=&postid=15083722#post15083722 target=_blank>Originally posted</a> by greenbean36191
It definitely looks like a sponge to me. If you really want to check, take a small bit of it and dissolve it in some bleach. There should be some spicules or sclerites left behind that you can examine under a microscope. Sponge spicules tend to be smooth and slender or very definite star-like shapes. Soft coral spicules tend to be more jagged, a little stumpier, and sometimes just small, spikey blobs. A google image search for "sponge spicules" and "coral sclerites" should give you an idea of the comparison.