Plenty, members of the family Xeniidae, the family Fungiidae (perhaps the genus Cycloseris), the order Zoanthidea, the phylum Porifera, and animals which I believe were of the family Siderastreidae. It's hard to be any more specific.
As an aside, here's something fascinating I found on Wet Web Media. I thought of Tony/Jon's orange M. capricornis colony when I read this but I'm sure it applies to many of our corals here:
"If you are keeping live Stony Corals, boring (as in digging, not yawning) species of Sponges of the genera Cliona (pictured, Cliona delatrix, the Red Boring Sponge; and Variable Boring Sponge, Siphonodictyon coralliphagum (3’s) are definitely out. However, strangely enough, if you find the Orange Icing Sponge, Mycale laevis (pictured) growing under your plate-type corals, this is not a "bad thing". This Sponge actually protects the Stony Coral from Boring Sponge infiltration."
(
http://www.wetwebmedia.com/sponges.htm)