A bony plate that covers the gills in crustaceans like crabs and lobsters.
From Greek branchia (gill) + osteon (bone) + -ite (indicating a structure or part), literally meaning 'gill-bone' in scientific nomenclature.
This is why crabs and lobsters can breathe underwater even without lungs—their gill covers (branchiostegites) protect and channel water across their feathery gills, like nature's own water filter system.
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