Grub shown in periodical taken (6)
I believe the answer is:
maggot
'grub' is the definition.
(I know that maggot is a type of grub)
'periodical taken' is the wordplay.
'periodical' becomes 'mag' (abbreviation for magazine).
'taken' becomes 'got' ('get' can be a synonym of 'take').
'mag'+'got'='MAGGOT'
'shown in' acts as a link.
(Other definitions for maggot that I've seen before include "Larva of housefly or bluebottle" , "Larva often found in decaying matter" , "Fly larva" , "immature flyer" , "Blowfly larva" .)