Alveoli are absent in which animals?

Alveoli are absent in animals that possess a different respiratory structure, such as insects and some amphibians. Insects utilize a tracheal system for gas exchange, where air diffuses directly through tubes called tracheae. Some amphibians, like certain larvae and adults, primarily rely on skin respiration or gills instead of alveoli for oxygen uptake. Thus, these animals have adapted alternative methods for respiration that do not involve alveolar structures.