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

The cephalopod group consists of living organisms such as octopuses, squids, cuttlefish, and nautiloids. They belong to the larger Phylum Mollusca, which also includes their relatives like snails and slugs.

Unlike most other mollusks, cephalopods possess a closed circulatory system. In this system, blood flows through a network of vessels that carry it back to the heart, rather than directly bathing the organs in blood fluid as seen in the open circulatory system of other mollusks.

For example, the octopus has a highly efficient closed circulatory system. Its blood remains confined within blood vessels, allowing it to be pumped precisely to different regions of the body. This is particularly important because the octopus has a large and complex brain, which requires a continuous and well-regulated blood supply for proper functioning. In contrast, mollusks like mussels and snails rely on an open system where blood flows freely around the organs.