A marine creature is a lone ranger? (3,4)

I believe the answer is:

sea lion

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'a marine creature' is the definition.

'is a lone ranger?' is the wordplay.
'is a lone' anagrams to 'SEA LION'.
However, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for sea lion that I've seen before include "one often immersed in salty water" , "Large-eared mammal of Pacific Ocean, like Leo" , "Marine animal, used as a circus performer" , "Creature" , "Acrobatic aquatic mammal" .)

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