Q. What is mechanical digestion? In molluscs, earthworms, arthropods, birds and vertebrates, in general, which organs respectively participate in this type of digestion?

Mechanical digestion is the fragmentation of food aided by specialized physical structures, such as teeth previous to extracellullar digestion, the mechanical fragmentation of food helps digestive enzymatic reactions because it provides a larger total area for the contact between enzymes and their substrates.

In some molluscs the mechanical fragmentation is done by the radula a teeth-like structure. Some arthropods, like dragonflies and lobsters, have mouthparts that make mechanical digestion of food. In birds and earthworms the mechanical digestion is made by an internal muscular organ. In mandibulate vertebrates there are chewing and mandibles muscles to triturate food previous to the chemical digestion.