Small deep-sea fish with a flattened body shaped like a hatchet blade, with large eyes and a silvery appearance.
Hatchet (from Old French hachette, diminutive of hache 'axe') + fish. The fish were named for their distinctive blade-like body shape that resembles a small axe head.
These fish are bioluminescent and create counter-illumination—they produce light on their belly to match the faint light from above, making them invisible to predators below. It's like nature's invisibility cloak!
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