The microscopic larval stage of a freshwater mussel, characterized by a shell with barbed hooks used to attach to fish.
From Greek glochis ('barbed point') + Latin diminutive -idium ('small'). The compound emphasizes both the small size and barbed nature.
A glochidium is so tiny (0.2-0.4mm) that you need a microscope to see it, yet it's armored with specialized hooks that can penetrate fish gill tissue—nature's engineering at a microscopic scale.
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