Croc is a surprise visitor on mediterranean island (7)

I believe the answer is:

corsica

I'm a little stuck... Click here to teach me more about this clue!

'mediterranean island' is the definition.
(I've seen this before)

'croc is a surprise visitor' is the wordplay.
'croc is a' can be anagrammed to 'CORSICA'.
Though, I'm not clear how the anagram is indicated.

'on' is the link.

Can you help me to learn more?

(Other definitions for corsica that I've seen before include "French Mediterranean island" , "Island N. of Sardinia" , "Island of W Italy, capital Ajaccio" , "Napoleon's island birthplace" , "Island north of Sardinia" .)

I've seen this clue in The Irish Times.

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