Nematocysts are specialized stinging structures found in certain aquatic organisms. They are not present in starfish (option 1) or centipedes (option 3) as these are terrestrial organisms. Ascaris (option 2), also known as a roundworm, is also a terrestrial organism and does not possess nematocysts. The correct option is 4, sea anemone. Sea anemones are marine organisms and possess nematocysts, which they use to capture prey and defend themselves. It`s worth noting that while the other options do not have nematocysts, they may have other specialized adaptations or defense mechanisms suited to their habitat and lifestyle.