Aurelia Aurita
The Aurelia Aurita is commonly known as the Moon Jellyfish, this jellyfish is commonly found throughout most of the Atlantic Ocean. This organism is translucent and has a diameter ranging from 25 to 40 centimeters. This organism also has four horseshoe-shaped gonads that can easily be seen through the top of it. It also restricted greatly and drifts with the current even when it swims.
The Aurelia Aurita does not have a cardiovascular system, and survives similarly to the Chironex Fleckeri (Sea Wasp) where it relies on diffusing its cells within the water to gain nutrients it needs, similarly, this organism also makes it contract the nutrients it needs through both the epidermis (which is its outer layer) and the gastrodermis (its inner layer). This is a perfect example that an organism does not need a proper cardiovascular system to survive. This lack of a system is also evident in its transparent body in case you do not believe me.