It will heal on it's own but there will be a ridge there, you can also super glue cleaned egg shell to the cracked area if you want it to be covered during the healing process.
The term apple snail is a blanket term used for many different types of snails. I assume that you are wanting diffusa, which are totally legal to own. www.msjinkzd.com is your best bet for quality snails.
With topics such as this additional information on the topic may no longer be helpful to the original posting op but may be helpful to someone who is currently looking for information about this subject ;)
if you got the crab out of the ocean it's saltwater and will die in the fresh water. The water that is leaking through the ceiling is collecting all kinds of things as it seeps through your ceiling which will result in death of everything.
That's correct but considering the roots of anubias are normally free floating in the water column or attached to something I do not see how a root tab placed into the substrate would be beneficial to an anubias.