In crustaceans and some other arthropods, a triangular plate or projection on the head situated above the mouth.
From Greek 'epi-' (upon) + 'stoma' (mouth); this variant spelling is used especially in crustacean anatomy rather than insect anatomy.
The same Greek root gives us words for different creatures—crabs have an epistome, insects have an epistoma, showing how evolution creates similar but different solutions for the same problems.
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