But despite the challenges, one scientist is known to have had long-term success with captive immortal jellyfish. dohrnii is sensitive, making it also difficult to rear in a lab for studies.

The jellyfish also must have perfect conditions where they aren't going to be harmed by anything external, such as by humans or other predators.'

Miranda explains, 'A lot of deep-ocean science takes a long time, and it is very costly to do observations over time to see change. Understanding how long jellyfish including T. Polyps are also practically defenceless to predation by animals such as sea slugs and crustaceans. For example, jellyfish, including immortal ones, are prey to other animals, such as fish and turtles. dohrnii may bend the rules to rejuvenate itself, but it can't always cheat death. The discovery, aided by the spectacular nickname 'immortal jellyfish', captured the world's attention. They continued to observe the jellyfish and found that, when stressed, the medusae would fall to the bottom of the jar and transform into polyps without fertilisation or the typical larval stage occurring. It was thought that these jellyfish would have to mature before spawning and producing larvae, but when the jar was next checked, they were surprised to find many newly settled polyps. Students Christian Sommer and Giorgio Bavestrello collected Turritopsis polyps, which they kept and monitored until medusae were released. It was 100 years later, in the 1980s, that their immortality was accidentally discovered. dohrnii was first described by scientists in 1883. 'We might be distracted watching much larger jellyfish, but the tiny things such as this can inform so much of our science about these animals,' says Miranda. This life cycle reversal can be repeated, and in perfect conditions, it may be that these jellyfish would never die of old age. They can then mature again from there as normal, producing new, genetically identical medusae. Transdifferentiation reprogrammes the medusa's specialised cells to become specialised polyp cells, allowing the jellyfish to regrow themselves in an entirely different body plan to the free-swimming jellyfish they had recently been. Medusa cells and polyp cells are different - some cells and organs only occur in the polyp, others only in the adult jellyfish. The process behind the jellyfish's remarkable transformation is called transdifferentiation and is extremely rare. This phenomenon has been likened to that of a butterfly which, instead of dying, would be able to transform back into a caterpillar and then metamorphose into an adult butterfly once again. Over the next 24-36 hours, this blob develops into a new polyp - the jellyfish's previous life stage - and after maturing, medusae bud off. It then settles on the seafloor as a blob-like cyst. When the medusa of this species is physically damaged or experiences stresses such as starvation, instead of dying it shrinks in on itself, reabsorbing its tentacles and losing the ability to swim. It has been dubbed the immortal jellyfish. The hydrozoan Turritopsis dohrnii, an animal about 4.5 millimetres wide and tall (likely making it smaller than the nail on your little finger), can actually reverse its life cycle.

Predator vs prey worksheet