Jellyfish emerge

500 million BCEPrimordial Sea

"Despite lacking blood, a heart, or a brain, slimy jellyfish are one of Earth’s most ubiquitous sea creatures and various species live in all of the planet’s oceans. They are some of the Earth’s oldest animals, having been around for roughly more than 500 million years . . . Jellyfish belong to a clade of animals called medusozoans, which includes the box jellies, hydroids, stalked jellyfish, and true jellyfish that swim in the oceans today. Medusozoans are part of the group Cnidaria, which also includes sea anemones and corals."

Laura Baisas, "Jellyfish may have been roaming the seas for at least 500 million years," Popular Science, August 2, 2023.

Image: Paulyn Cartwright, Susan L. Halgedahl, Jonathan R. Hendricks, Richard D. Jarrard, Antonio C. Marques, Allen G. Collins, Bruce S. Lieberman, CC BY 3.0, via Wikimedia Commons