By definition, these animals select food based on size. A good example is found in bivalves which use their gills to filter passing water. Solid material sticks to a mucous track and is carried to the mouth by cilia where it is ingested. An external type of digestion is sucking or fluid feeding . A wide variety of animals and insects are adapted to take in liquid food, either from plants or animal juices.
All spiders use sucking as their digestive means.
They inject digestive enzymes into the prey and allow the exoskeleton to contain the juice as internal body parts are liquified. Seizing food and Trituration refers to the technique of breaking up food mechanically. The term is derived from grinding corn to a powder. Teeth, claws, gizzards, etc. Grazing as done with a radula as in molluscs and grinding tough plant food with molars.