Plural of branchus; a rare or archaic form referring to gills or gill-like structures.
From Latin 'branchia' (gill), with branchi as an alternate plural or Latinized form. This is an uncommon variant found mostly in historical scientific texts.
Ancient zoologists invented 'branchi' to describe the mysterious feathery structures that let fish breathe underwater—it took centuries to understand these aren't lungs but incredibly efficient gill systems.
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