The Class Maxillopoda is a diverse group of small crustaceans that includes barnacles, copepods, and related species. Most are aquatic, living in marine or freshwater environments, and many are planktonic or sessile. Maxillopods typically have a compact body with a reduced abdomen, specialized appendages for feeding and swimming, and simple or no eyes. They play important ecological roles as filter feeders, planktonic grazers, and as a food source for larger animals, and some, like parasitic barnacles, have unique adaptations to attach to hosts.