Roofer found an isopod crustacean (6)

I believe the answer is:

slater

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'crustacean' is the definition.
(slater is a kind of crustacean)

I cannot understand how the rest of the clue works.

(Other definitions for slater that I've seen before include "High-up person" , "Professional roof worker" , "Does one abuse" , "Roof-worker" , "Man on top" .)

I've seen this clue in the Sydney Morning Herald.

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