Here's why:
* General Rule: Most nouns ending in "y" preceded by a consonant form their plural by adding "ies".
* Exceptions: There are a few exceptions, such as words ending in "quy", "guy", or "by", where you just add an "s".
You would never put parentheses around "and countries", as that would be grammatically incorrect. The correct way to write it would be:
Example: The survey included data from several different countries, including France, Germany, and Italy.