Fungus father's found on corgi's extremities (7)
I believe the answer is:
candida
'fungus' is the definition.
(candida is a kind of fungus)
'father's found on corgi's extremities' is the wordplay.
'father' becomes 'da' (da can mean dad).
'found on' means one lot of letters go next to another.
'corgi's extremities' becomes 'candi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'da' after 'candi' is 'CANDIDA'.
Can you help me to learn more?
(Other definitions for candida that I've seen before include "by G.B. Shaw" , "Fungus" , "GBS play" , "Parasite" .)