Marine animal consuming rubbish is an edible mollusc (3,5)
I believe the answer is:
sea snail
'edible mollusc' is the definition.
'sea snail' can be an answer for 'mollusc' (I have seen 'Marine mollusc ' mean 'sea snail' so perhaps 'mollusc' could also mean 'sea snail'). I am unsure of the 'edible' bit.
'marine animal consuming rubbish is an' is the wordplay.
'marine animal' becomes 'seal' (I've seen this in another clue).
'consuming' indicates putting letters inside.
'rubbish' is an anagram indicator (a poor quality or rubbish spelling of the letters).
'is'+'an'='isan'
'isan' is an anagram of 'snai'.
'seal' placed around 'snai' is 'SEA-SNAIL'.
Can you help me to learn more?
(Other definitions for sea snail that I've seen before include "Spiral-shelled marine mollusc" , "Creeping marine creature with a spiral shell" , "wet crawler" .)