The "shells" are the seed covers and can hang around and on the first leaves for months. They will fall off at some point.
What Xeramtheum said.
Also - there is no reason to repot a seedling until it is 3 - 4 inches tall - 2-3 at a minimum.
If you have a fan - run it.
If you have a heat mat, keep it on til you have 2 sets of true leaves.
Label everything!
Algae is an indication of too wet soil!! Sprinkle some cinnamon on it and it should kill it.
Grow seeds in seed staring media - not potting soil.
If you use humidity domes, remove them at this point.
