Why octopus has closed circulatory system while as all other mollusca have open circulatory system?

The cephalopod group includes the living octopuses, squid, cuttlefish, and nautiloids. They are nestled within the larger Phylum Mollusca - the mollusks, which also include the cephalopod cousins, snails and slugs.

Unlike all other mollusks, cephalopods have aclosed circulatorysystem. This means that blood flows through a series of vessels to return to the heart, rather than bathing organs in the blood fluid as inopen circulatory systems.

octopus has closed circulatory system which means blood is contained in a network of blood vessels inside the body. These vessels allow blood to be pumped to specific areas of the octopus rather than bathing all their internal organs like the other molluscs like mussel and snail do. This is useful because the octopus has a large brain and therefore needs a lot of blood to allow for best function.