Cotyledon

This is a sign to either bury the seed slightly deeper or tamp down the soil above it a bit more tightly -- small adjustments. if you adjust based on frequency of this occurring, you'll mostly avoid it while still minimizing sprout times as best possible. burying it too deeply or compacting substrate too tightly on top will slow down a sprout, but also create enough friction to rip that shell off before it sprouts. Withing a few grows you'll have a really good feel for it, if you pay attention and adjust. They "can" recover, but with an autoflower, this might mean a 7-10gram plant when it's all done and dried to smoke. At the least, a lesser yield of some proportion relative to how long it takes to recover. looks like you still have a growth tip? if you got nothing else goin on let it go another 7-10 days and if it's not too far behind, it'll be okay... if it's still a nub, might as well throw it out. could let it run next to whatever else you plant in meantime.. if it doesn't take up needed space... or until it does.. can see first hand the effect it had. good learning experience at the least and watering doesn't cost much, and if the light is going to be on anyway with another plant it's not really an added cost. i've left shells on seedlings before and did not like the results. There is a way to carefully remove the shell and virtually eliminate risk of damaging the plant. Hold one side of the split shell with tweezer -- in a way that hold the entire plant steady from bottom of stem all the way to the shell you hold. Hold this steady at all times -- eliminates stress on roots and stem etc. Using anything like a toothpick, gently pry the shell open while holding entire plant steady with tweezers. Just touching edge of shell.. pressing away from tweezers in a couple spots if necessary to get the right leverage. it'll split right open and fall off. If there is a little membrane holding the leaves together, gently poke tip of toothpick near bottom of leaves just inside the membrane and slide it off the ends of the cotyledons -- dont try to rip the membrane.. it will slide off much easier with zero stress to the cotys. i find some really strong reading glasses helps, lol.... or one of those magnifying glasses with its own stand etc... makes it easy to see where you can place the tweezers and toothpick without even touching the cotys and purley putting pressure on the shell alone. If i see a shell, i take it off asap, otherwise the plant falls behind.. each day it does not have light hitting the cotys slows it down significantly, in my experience. I don't want plants wil 5-7days difference due to varying germination rates or setbacks like a shell being stuck. I'd probably throw a plant out if it's 1 week behind the others.. it's never going to fit in my canopy and i'llhave to spend an extra week of electricity just to even out the canopy... no thanks in a larger garden.. but, less of a cost in a small garden.