It looks like a piece of the membrane inside the seed shell is still attached..........preventing the cotyledons from opening.
Mist it with water to soften it and gently remove with a toothpick.
I thought it was fried from the soil until @mick Foster posted....I'm new at Cannabis too. I had the same issue with a membrane last grow and did just what Mick suggested.
It looks like a piece of the membrane inside the seed shell is still attached..........preventing the cotyledons from opening.
Mist it with water to soften it and gently remove with a toothpick.