I recently visited the Monterey Bay Aquarium which has several spectacular displays of jellies.
These animals, formerly referred to as "jellyfish", are some of the simplest animals on Earth. The term jellyfish is misleading since these animals are not fish at all, but very different creatures. They typically catch their food using stinging cells which inject venom into the animal's prey. The name of their Phylum comes from "cnidos," which means stinging nettle. If you have come into contact with one of these animals then you understand the meaning on a very personal level. By the way, vinegar helps to relieve the pain of the sting.
Related to the Jellies are another group of animals you may have seen in tide pools called sea anemones. Anemones also have stinging cells, but like their relatives the coral, many farm algae in their bodies. The algae make food from sunlight, and in some cases provide up to 90% of the nutrition for the coral or anemone. It is the algae partner that gives this anemone its color.
Some jellies also farm algae, such as these upside down jellies. They float up to the top of the water column during the day to provide sunlight to their algae partners.
I am fascinated by these beautiful animals. It's true they pack a sting, but all animals have to eat right? If you would like to learn more about these animals, and see a short video of the way they move click here to go to one of Monterey Bay Aquarium's webpages about the jellies.