Work after month to find sea creature (7)
I believe the answer is:
octopus
'sea creature' is the definition.
(I've seen this before)
'work after month' is the wordplay.
'work' becomes 'opus' (I've seen this before).
'after' means one lot of letters go next to another.
'month' becomes 'oct' (Oct is an example).
'opus' put after 'oct' is 'OCTOPUS'.
'to find' is the link.
(Other definitions for octopus that I've seen before include "Creature with eight tentacles" , "Spineless creature" , "Sea creature - pulpo on a Spanish menu" , "Eight-legged creature" , "Large marine mollusc" .)