Need Help to identify this critter and clown?

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#1. Anyone know what this is? Its about 3/4 inch long, has a tiny flat hard shell on top of its back it looks and moves fast, maybe a nudibranch or snail? Any ideas? Came on a small piece of live rock, should I leave it in the tank or could it be harmful?



#2. Also, I bought a clown that was sold as a maroon clown and is the color of a maroon but the shape and stripes are identical to a percula. Two pics below show different lighting so the color is hopefully more obvious. My books show the maroon stripes and head shape slightly different than a percula, anyone here know which this is for sure?