Swimmer heading for airboat in Kent bay? (8)
I believe the answer is:
seahorse
'swimmer' is the definition.
(seahorse is a kind of aquatic vertebrate)
'heading for airboat in kent bay?' is the wordplay.
'heading for' says to take the initial letters.
'in' is an insertion indicator.
'kent' becomes 'se' (Kent is part of the South East of England).
'bay?' becomes 'horse' (bay is a kind of horse**).
The first letter of 'airboat' is 'a'.
'se'+'horse'='sehorse'
'a' inserted inside 'sehorse' is 'SEAHORSE'.
(Other definitions for seahorse that I've seen before include "marine creature" , "that's found in the main" , "Fish" , "swimmer" .)