Heroic men at sea bringing in dead marine creature (10)
I believe the answer is:
echinoderm
'marine creature' is the definition.
'echinoderm' can be an answer for 'creature' (echinoderm is a kind of animal). I'm not sure about the 'marine' bit.
'heroic men at sea bringing in dead' is the wordplay.
'at sea' indicates anagramming the letters.
'bringing in' is an insertion indicator.
'dead' becomes 'd' (abbreviation in government records).
'heroic'+'men'='heroicmen'
'heroicmen' anagrammed gives 'echinoerm'.
'echinoerm' placed around 'd' is 'ECHINODERM'.
Can you help me to learn more?
(Other definitions for echinoderm that I've seen before include "Maybe urchin" , "Eg, sea urchin" , "sea creature" .)