Past participle or adjectival form meaning having equal valves or shells.
From 'equivalve' with the past participle suffix '-ed', though 'equivalve' is already an adjective, making this form redundant or emphatic in rare technical usage.
This word is so specialized that it appears almost nowhere in modern biology texts—scientists prefer just 'equivalve'—but it represents a ghost of older English medical and scientific writing when redundant forms were common in scholarly writing.
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