Does anyone know anything about gardening?

I have a bunch of lemon tree seedlings that I grew, proudly, from an actual lemon last year. They've been doing ok, and I put them out for the summer to get some sunshine. Unfortunately slugs or snails have taken an interest in some of them and have done that thing where they eat the outer coating off the seedling stems (I don't know the right word for it, "bark" is as close as I can get but obviously it's not really bark). They've left the sort of woody core on the attacked seedlings alone.

2 questions:

1. What is the correct terminology for the bit they've eaten so I can google for it?
   
2. Is there anything immediate I can do to help the ones that were attacked? It's getting cold enough for me to consider moving them back indoors, so further pest attacks aren't a major problem now. The attacked ones have plenty of new growth but it's a bit stunted - hard to say whether that's due to the damage or breeding or whatever. Any good ideas?