In gospel truth this reptile goes backwards (6)

I believe the answer is:

turtle

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'this reptile goes backwards' is the definition.
'turtle' can be an answer for 'reptile' (turtle is a kind of reptile). I'm unsure of the rest of the definition.

'in gospel truth' is the wordplay.
'TURTLE' is hidden backwards within the letters.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for turtle that I've seen before include "Sea-creature resembling tortoise" , "Shelled marine creature" , "Kind of sea-tortoise, noted for soup" , "Mock or Teenage Ninja?" , "Sea creature like tortoise" .)

I've seen this clue in The Times.

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