Plural of delthyrium; openings or notches in the shell structures of certain brachiopods (ancient sea creatures), located along the hinge region.
From Greek 'delthyra' meaning 'door' (from 'delthys' meaning threshold). Applied in paleontology to describe the distinctive portal-like openings in brachiopod shells.
Brachiopods look like clams but they're completely unrelated, and scientists use features like delthyria to identify different ancient species—these shell openings are like fingerprints that tell us which creatures roamed the Paleozoic seas.
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