New pen, say, Charlie gently agitated with line not appearing (6)
I believe the answer is:
cygnet
'new pen' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe you can see a link between them that I don't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for cygnet that I've seen before include "Immature swan" , "that's no ugly duckling" , "Young swan" , "small pen? Possibly" , "Little swan" .)