Biology
Jellyfish are made up of 95% of their body of water
Lacking brains, blood, or even hearts, jellyfish are pretty simple critters.
They are composed of three layers: an outer layer, called the epidermis; a middle layer made of a thick, elastic, jelly-like substance called mesoglea; and an inner layer, called the gastrodermis. An elementary nervous system, or nerve net, allows jellyfish to smell, detect light, and respond to other stimuli.
The simple digestive cavity of a jellyfish acts as both its stomach and intestine, with one opening for both the mouth and the anus.
The bodies of most range in size from about 2 to 40 cm (1 to 16 inches) in diameter; some species are considerably larger, however, with diameters of up to 2 metres (6.6 feet).
Scientific insights about Jellyfish
https://ocean.si.edu/ocean-life/invertebrates/jellyfish-and-comb-jellies
https://www.britannica.com/animal/jellyfish
https://magazine.caltech.edu/post/the-wonders-of-jellyfish
https://www.cell.com/current-biology/pdf/S0960-98221300359-X.pdf
https://thebiologist.rsb.org.uk/biologist-features/everlasting-life-the-immortal-jellyfish
https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.11741
https://www.nhm.ac.uk/discover/immortal-jellyfish-secret-to-cheating-death.html