Swimmer able to do the crawl? (9)

I believe the answer is:

amphibian

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'swimmer' is the definition.
(I know that amphibian is a type of Tetrapoda)

I don't understand the rest of the clue.

(Other definitions for amphibian that I've seen before include "Eg, newt or toad" , "Frog for one" , "Animal that lives on land and in water" , "Vehicle for use on land or water" , "One lives on land and in water" .)

I've seen this clue in The Telegraph.

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