Biology / Unit 10 Bio 2245 short lesson, about 20 seconds
Cnidocytes and Nematocysts
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The idea
A cnidarian's defining structure is the cnidocyte, a cell housing a coiled, harpoon-like nematocyst that fires on contact to capture prey.
In practice
A jellyfish's tentacle fires thousands of nematocysts on contact, injecting venom that can subdue small prey or harm a larger animal.
Where people slip
Nematocyst discharge is a one-time event — a fired nematocyst cannot retract or fire again without being replaced.
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