Physalia Physalis
The Physalia Physalis is commonly known as the Portuguese Man o' War and its tentacles can cause a deadly, venomous sting. This jellyfish is a siphonophore, which is not an ordinary multicellular organism. The Portuguese Man o' War is made of a colony of individuals called zooids, which attach to each other and are almost completely incapable of surviving by itself.
Unsurprisingly, due to the fact that it falls under the category of Cnidaria, the Portuguese Man o' War does not need a circulatory system and therefore, does not have one. It gets all of its necessities for survival such as oxygen and nutrients by diffusing its cells with the water that it is surrounded by and in contact with through the epidermis (outer layer) and then through the gastrodermis (inner layer). In addition to this, this organism also has no heart at all.
Unsurprisingly, due to the fact that it falls under the category of Cnidaria, the Portuguese Man o' War does not need a circulatory system and therefore, does not have one. It gets all of its necessities for survival such as oxygen and nutrients by diffusing its cells with the water that it is surrounded by and in contact with through the epidermis (outer layer) and then through the gastrodermis (inner layer). In addition to this, this organism also has no heart at all.