Getting Food - Food is always an important part of life. The Common Octopus catches its food either by ambush or by chasing it down. For crabs or oysters the octopus will just grab onto the prey and either kill it on the spot and bring back to its den, or it will bring it back to its den alive. Octopuses have been know to carry clams or oysters back to their home and place them right outside. This way whenever the octopus is hungry it can reach outside and grab a bite to eat. For faster prey such as fish, the octopus will camouflage itself and reach out an arm or two as the fish swims by and grab it.
Eating - The actual act of eating is very simple. The octopus will use the many suckers on the underside of its tentacles to usher the food from the outside toward the center of its body where the beak is. The beak is very useful in crushing the exoskeletons of crustaceans and cracking the shells of oysters or clams. Once the exterior of the prey is penetrated, the octopus will expel the non-edible parts and ingest the yummy stuff.
A Host? - So far as I, and science can tell, Octopus vulgaris is not a host to anything. Although scientists do suspect that like everything they are susceptible to being infested with something. But in general the octopus is not known to be a primary or secondary host to anything.
Digestion - The digestive tract is complete and ciliated, with a mouth, stomach, and anus. The octopus eats, and then the stomach digests the food. Digestive glands sift through the food and transfer the useful nutrients into the blood stream which caries them throughout the body. The non-useful stuff is bundled up and expelled into the water.
Circulation - The octopus has three hearts and an open circulatory system. Two of the hearts are called "gill hearts" and are located right by the gills. The third heart is only used for pumping blood.