Jellyfish

Jellyfish were a type of marine-dwelling organism native to Earth. There were also jellyfish-like creatures spread far and wide across the universe.

When Fu Peng invited the Third Doctor to dinner, he told him they were having dried squid and stewed jellyfish. (TV: The Mind of Evil)

Thawn called Kroll an "overgrown jellyfish". (TV: The Power of Kroll)

Giant creatures which looked like jellyfish lived on Jobis. (AUDIO: The Rocket Men)

According to Olivia Colasanto, there was a type of jellyfish on Earth that was able to revert to a youthful state, rendering it functionally immortal. She speculated that there were some jellyfish who had lived for thousands of years. (TV: End of the Road)