Officer in prison riot reveals venomous creature (8)
I believe the answer is:
scorpion
'venomous creature' is the definition.
(I've seen this before)
'officer in prison riot' is the wordplay.
'officer' becomes 'co' (Commanding Officer abbreviation).
'in' indicates putting letters inside.
'riot' indicates anagramming the letters.
'prison' anagrammed gives 'srpion'.
'co' placed into 'srpion' is 'SCORPION'.
'reveals' acts as a link.
(Other definitions for scorpion that I've seen before include "Arachnid with venomous sting" , "Stinger with a long tail" , "Small spider with pincers and stinging tail" , "Kind of arachnid with pincers and stinging tail" , "Kind of spider with pincers and stinging tail" .)