Aquatic invertebrates are a diverse group of animals that inhabit freshwater and marine ecosystems. They lack a backbone and come in a variety of shapes and sizes, ranging from microscopic organisms like rotifers and water fleas to larger species such as crayfish and jellyfish. Aquatic invertebrates play important roles in nutrient cycling, food webs, and ecosystem health. They are also commonly used as indicators of water quality and environmental health in aquatic ecosystems. Researchers studying aquatic invertebrates may investigate their physiology, behavior, ecology, interactions with other organisms, and responses to environmental stressors such as pollution and climate change.