Crossword Genius

Paleozoic fossil with a three-part exoskeleton (9)

Ross

I believe the answer is:

trilobite

(Other definitions for trilobite that I've seen before include "find on Lyme Regis beach?" , "Extinct arthropod" , "Extinct animal" , "old crawler" , "Bitter oil (anag.)" .)

I've seen this clue in The Guardian.
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