What has a capsule with a coiled threadlike structure that helps it capture food?

The organism you are referring to is likely a type of cnidarian, such as a jellyfish or sea anemone. These creatures possess specialized cells called cnidocytes, which contain a capsule known as a nematocyst. When triggered, the nematocyst releases a coiled thread that can capture prey and deliver toxins, aiding in their feeding process.