Power or composure this sea creature has (8)
I believe the answer is:
porpoise
'this sea creature has' is the definition.
'porpoise' can be an answer for 'sea creature' (porpoise is a type of sea creature). I'm not certain of the rest of the definition.
'power or composure' is the wordplay.
'power' becomes 'p' (symbol in physics).
'composure' becomes 'poise' (poise is a kind of composure).
'p'+'or'+'poise'='PORPOISE'
Can you help me to learn more?
(Other definitions for porpoise that I've seen before include "Animal" , "Small aquatic mammal with blunt snout" , "Member of dolphin family" , "Small whale with blunt snout" , "Sea beast" .)