It's the "@" sign, and it was added so hams could give each other their
e-mail addresses easier. It will be ".--.-." (which is "a" and "c" with no
space between them).

Very good. Now what does a CW op send for a plain space or a space indicated by
an underline?

I suppose the former may be ignored, but I don't believe the latter would be.

Bill, K5BY