What is this close-up picture? (WotsThat: sea urchin spine (macro))

Question

What object is shown in this zoomed-in close-up photo?

Accepted Answer

sea urchin spine (macro). Sea Urchin Spines: Nature's Hydraulic Daggers Sea urchin spines are actually hollow tubes filled with fluid, and the creature can extend or retract them using hydraulic pressure—essentially weaponizing water the same way construction equipment does. This ingenious system means a sea urchin can stab a predator with surprising force and speed without needing any muscles inside the spine itself.

Answer: sea urchin spine (macro)

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