Greek character throws up less seafood (6)
I believe the answer is:
'seafood' is the definition.
(mussel is a kind of seafood)
'greek character throws up less' is the wordplay.
I cannot really see how this works, but
'character' could be 'mu' (Greek letter) and 'mu' is found in the answer.
an anagram of 'less' is 'ssel' which is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mussel that I've seen before include "Pearl may come from it", "Bivalve with purple-black shell", "Black marine bivalves", "Common edible marine mollusc", "Edible shellfish".)