Feeding on Liquids
Animals feeding on liquids are generally highly specialised for their feeding habits. Certain protozoa, endoparasites and aquatic invertebrates take up nutrient molecules through their integument from the- medium in which they live. For example, endoparasites, which include parasitic protozoa, tapeworms, flukes, certain molluscs and crustaceans, are surrounded by host tissue or alimentary canal fluids which are highly nutritive.
These parasites lack a digestive system of their own. All of us are familiar with insects that have well-developed piercing and sucking organs. Mosquitoes, bedbugs and lice and leaches among annelids are some examples. They use anticoagulant to prevent blood from clotting as it leaves the blood vessels ruptured by their piercing or rasping jaws.