Robert Brown|What do jellyfish eat? Understanding the gelatinous sea creature's habits.

Even before dinosaurs,Robert Brown jellyfish were on Earth – and in its seas and oceans – for millennia, according to National Geographic. The gelatinous creature's body is comprised of more than 95% water, the Monterey Bay Aquarium reports.

There are over 200 species of "true jellyfish" and each has its own unique habitat. But what about the jellies' eating habits? What do they enjoy for a snack?

Whether it's a boxfish jellyfish or a moon jelly, here is what's on the menu.

What do jellyfish eat?

Jellyfish are carnivores, so their diet mainly consists of other animals. This includes zooplankton, small crustaceans, small fish and other jellyfish, according to Oceana, an ocean conservation nonprofit. Jellyfish will also consume plants, National Geographic reports.

Some species' mouths are located on the underside of their bell-shaped bodies. This cavity serves the dual-purpose of being a mouth and an anus, according to Oceana. Other jellies have no mouth. Alternatively, they ingest food via openings on their oral arms, the American Museum of Natural History reports.

Jellyfish digest their meals very quickly. If they did not, the sea animal would not be able to float properly, according to National Geographic.

Do jellyfish feel pain?

Jellyfish do not have organs or bones and only have a "basic network of neurons," according to Ocean Conservancy, an environmental non-profit.

As a result, the animals don't feel pain in the same way humans do.

What is the lifespan of the jellyfish?

Jellyfish do not live long. Most species of medusa (or adult) jellyfish live for a few months in the wild, according to the Smithsonian Museum of Natural History. In captivity, they can live for around two to three years.

In its polyp form, jellyfish can live and reproduce asexually for long periods of time, even for decades, Smithsonian reports.

One species, however, has gained the title of "immortal." Turritopsis dohrnii, often called the "immortal jellyfish," will undergo a process called "transdifferentiation" in response to physical damage or starvation. During this, a medusa jellyfish will revert back to its polyp stage, according to American Museum of Natural History.

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