Well, if you consider the Animalia regnum, then it's certainly a very unique case, in which the cells of the main body act like perpetual steam cells, able to differetiante and return to the original state constantly.
The DNA repair system of that jellyfish must be nothing short of amazing, if you take in consideration that a normal DNA repair system in animals corrects 10^6 mutations per replication cycle, and the Telomerase (The enzyme which repairs the Telomers, the terminations of each chromossome which dictate chromossomical age) can repair 10^4 uncopied Telomers. Even so, most animals have limited time span due to continuous DNA degradation, even with the DNA repair system.
But this case is nothing new if you look into the Prokaryota regnum (bacteria and archae), since the specimens of that regnum have a separate DNA system, the Plasmid DNA. That system is used to create proteins and enzymes that can protect the Prokaryotes from virtually anything, and have massive DNA repair systems.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"