New Mushrooms :D

So I went into petco to night and I got some food, 10 snails, 2 peppermint shrimp (hopefully theyll take care of the aptasia) 1 fairy wrasse (that has gone into hiding...she looked stressed when i put her in the tank...I hope she makes it) And one rock of 7 bright green mushrooms. I'm wondering, there is some black slimy stuff on it that looks like 2 slugs on the side of the rock. Does anyone have any Idea what it is? My guess is some type of algae??
Anyways, heres some pics!




and the mushrooms.....





And this is the pic that shows the black stuff, its down on the bottom right by the two mushrooms.




Thanks!