Jeopardy host returned holding aquatic creature (5)
I believe the answer is:
hydra
'aquatic creature' is the definition.
(type of aquatic invertebrate)
'jeopardy host returned holding' is the wordplay.
'holding' indicates the answer is hidden within the clue.
'returned' is a reversal indicator.
'ardyh' can be found hidden inside 'jeopardy host'.
'ardyh' backwards is 'HYDRA'.
(Other definitions for hydra that I've seen before include "M any-headed monster fought by Hercules" , "Small red-berried tree" , "Many-headed snake slain by Hercules" , "Mythological water-monster" , "Multi-headed monster slain by Hercules" .)