Animal turned by shipwrecked sailor into soup? (6)

I believe the answer is:

turtle

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'soup?' is the definition.
(turtle soup is a kind of soup)

I cannot understand how the rest of the clue works.

(Other definitions for turtle that I've seen before include "Shelled marine creature" , "Shelled reptile" , "Sea swimmer" , "Marine reptile of the order Chelonia" , "Kind of sea-tortoise, noted for soup" .)

I've seen this clue in The Globe and Mail.

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