Flag up puzzle feature on the perimeter - snails (8)
I believe the answer is:
neritina
'perimeter snails' is the definition.
'neritina' can be an answer for 'snails'. I'm not certain of the 'perimeter' bit.
'flag up puzzle feature on' is the wordplay.
'flag' becomes 'tire' (I've seen this in another clue).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'puzzle feature' becomes 'nina' (crossword thing where corners spell something).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'tire' reversed gives 'erit'.
'erit' placed inside 'nina' is 'NERITINA'.
'the' is the link.
Can you help me to learn more?
(Another definition for neritina that I've seen is " Family of molluscs".)