Well, I was taking down my dwarf tank for a good cleaning; had some hair algae issues.
I also wanted to make a few adjustments to the tank. Moved all the ponies to a 10g and found this under some rocks when I was taking rocks out.
Weird thing was that when I had set that tank up I knew it was going to be dwarf seahorse specific, with only the dwarfs, a few snails and some mysid shrimp so I treated the tank with panacur. I last added a little panacur about 6 months ago.
Panacur is supposed to leach into rock and sand and probably everything else... interesting that this survived. I'm tempted to put a zoo in that tank to see how it does. I've thought about putting a gorgonian in that tank; but have read they don't do well with panacur.
So, I stuck all the rock that was in that tank in the freezer in case there was any other anemone-type critters on them that I didn't see.