In Time, Mona found an extinct marine cephalopod mollusc (8)
I believe the answer is:
ammonite
'extinct marine cephalopod mollusc' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'in time mona found an' is the wordplay.
'in' means one lot of letters goes inside another.
'time' becomes 'am'.
'mona' becomes 'monte' (I can't explain this - if you can you should believe this answer much more).
'found' says to put letters next to each other.
'an' becomes 'i' (Roman numeral for one).
'am'+'monte'='ammonte'
'ammonte' enclosing 'i' is 'AMMONITE'.
Can you help me to learn more?
(Other definitions for ammonite that I've seen before include "shelled to extinction?" , "Common fossil" , "old nomadic tribesman" , "Type of fossil" , "Type of explosive" .)