Maxillopoda is a class of small crustaceans that includes barnacles, copepods, and fish lice. They are characterized by their unique body structure, which often features a reduced abdomen and a large head. Maxillopods are found in various aquatic environments, from oceans to freshwater habitats, and play important roles in the food web. Most maxillopods are filter feeders or parasites, with some species forming symbiotic relationships with other marine organisms. They have a wide range of adaptations that allow them to thrive in diverse ecological niches, making them an essential component of aquatic ecosystems.