Final answer:
Cnidarians use specialized structures called nematocysts housed within cnidocytes for defense and prey capture, which function by firing toxins through a coiled thread and barb when triggered.
Step-by-step explanation:
The unique stinging intracellular structures that assist a typical cnidarian in defense and prey capture are known as nematocysts. These specialized organelles are housed within cells called cnidocytes, which are found predominantly around the mouth and tentacles of cnidarians, such as jellyfish, corals, and sea anemones. Nematocysts contain a coiled thread paired with a barb, functioning like a harpoon. Upon contact, they can rapidly eject this thread, delivering toxins to immobilize prey or defend against predators. This mechanism involves a hairlike projection called a cnidocil, which is highly sensitive to touch and triggers the firing of the nematocyst with incredible acceleration.