Jellies

The moon jellyfish, Aurelia aurita, aka saucer jelly, moon jelly and common sea jelly, can be recognized by their delicate and exquisite coloration, often in patterns of spots and streaks.

Aurelia swim by pulsations of the bell-shaped upper part of the animal.

Feeding and swimming is directed by a nerve inside the jellyfish, but this animal is only capable of limited motion; most of the time it just drifts around in the ocean.

Swimming mostly functions to keep the animal at the surface of the water rather than to make progress through the water. They swim horizontally, keeping the bell near the surface at all times. This allows the tenticles to be spread over the largest possible area, in order to better catch food.
The bottom of the medusa is fitted with tentacles which are used for catching prey. The tentacles of the moon jelly are harmless to humans.

A lot of predators like to eat moon jellyfish, including certain birds, fish, and sea turtles. Humans also like to eat moon jellyfish, especially in South-East Asia. Would you like some peanut butter with that?