Rodent marks domestic ’abitat? (5)
I believe the answer is:
mouse
'rodent' is the definition.
(mouse is a kind of rodent)
'marks domestic 'abitat?' is the wordplay.
'marks' becomes 'M' (former German currency).
'domestic 'abitat?' becomes 'ouse' (house said with the H dropped as in habitat).
'm'+'ouse'='MOUSE'
(Other definitions for mouse that I've seen before include "retiring person" , "Small verminous rodent" , "whose movements are captured on screen" , "Timid fellow" , "Cursor control" .)