Not sure about the first one but the second one is a flat worm and you want to get rid of those asap before you get too many. You can take them out manually whenever you see one, others will have more ideas for you I haven't ever had them but know they are bad.
I think Sara is correct on the first pic, upside down jellyfish and second pic, Chiton. At least that is what it **seems without a better pic.