Smooth American painter in small jumper (10)
I believe the answer is:
sandhopper
'painter in small jumper' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe there's a link between them I don't understand?
'smooth american' is the wordplay.
'smooth' becomes 'sand' (sanding is a kind of smoothing).
'american' becomes 'hopper' (I can't justify this - if you can you should give a lot more credence to this answer).
'sand'+'hopper'='SANDHOPPER'
Can you help me to learn more?
(Other definitions for sandhopper that I've seen before include "jumper for the beach?" , "tiny crustacean" .)