Polychaetes are a class of annelid worms, characterized by their segmented bodies and bristle-like structures called setae. They are primarily found in marine environments, living in various habitats such as sandy or muddy sea floors. Polychaetes play a crucial role in the ecosystem by contributing to nutrient cycling and serving as a food source for many marine animals. These worms exhibit a wide range of sizes and colors, with some species being only a few millimeters long while others can grow over a meter. Polychaetes can be free-living or burrowing, and many have specialized structures for locomotion and feeding. Their diverse adaptations allow them to thrive in different ecological niches within the ocean.