Moon Jelly - Gonads Visible Through Its Head
Not much is really known about the Aurelia aurita, but it is commonly known as the "moon jelly", so that automatically makes it one of the more interesting species of jellyfish. Only growing to a little over a foot in diameter, the moon jelly is commonly recognized by its four horseshoe shaped gonads, that can be seen through the top of its head.
This species of jellyfish feeds by pulling medusae, fish eggs, mollusks, and plankton into its body with its long tentacles (where it breaks them down through an enzymatic process), but it's unable to hunt for prey due to its primary mode of transport; drifting.
The moon jelly basically goes where the ocean takes it, which happens to be all over the world. Despite having a fairly efficient way of breathing through its outer membrane, the moon jelly has a very short lifespan of just a few months, that is often made even shorter by its inability to escape predators like sunfish and sea turtles. How do you run (or swim) away when you're a drifter? The species is literally dependent on life's currents (ocean currents) to take it to its fate. It remains a thriving species however, through a fairly high reproduction rate and an ability to fend off at least some of said predators with its tentacles.