Light vehicle going around head of rare crustacean (4,4)
I believe the answer is:
land crab
'crustacean' is the definition.
(I've seen this before)
'light vehicle going around head of rare' is the wordplay.
'light' becomes 'land' (I've seen this before).
'vehicle' becomes 'cab' (cab is a kind of vehicle).
'going around' is an insertion indicator.
'head of' indicates taking the first letters.
The initial letter of 'rare' is 'r'.
'cab' going around 'r' is 'crab'.
'land'+'crab'='LAND-CRAB'
(Other definitions for land crab that I've seen before include "Violent criminal" , "Burrowing crustacean" , "Mainly terrestrial crustacean" , "one with nippers" .)