They tend to be known only as parentheses (singular - "parenthesis") or brackets.
round brackets, open brackets or parentheses: ( ) square brackets, closed brackets or box brackets: [ ] curly brackets, squiggly brackets, swirly brackets, braces, or chicken lips: { }
Cathos is the German spelling of the Spanish name Catos.
Another name for screen name is 'nickname' or 'user name'. The use of the term "logon" might also apply.
title, epithet
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