Mollusc has month to work (7)
I believe the answer is:
octopus
'mollusc' is the definition.
(I know that cephalopod parent taxon mollusc)
'month to work' is the wordplay.
'month' becomes 'oct' (abbreviation for October).
'to work' becomes 'opus' (an opus is an artistic work).
'oct'+'opus'='OCTOPUS'
'has' acts as a link.
(Other definitions for octopus that I've seen before include "Influential person" , "army swimmer" , "Sea creature's tentacles served as food" , "Eight-armed creature" , "Sea creature - pulpo on a Spanish menu" .)