start their lives as a larva that metamorphoses into a polyp; a tiny sea anemone. When the conditions are right, these polyps bloom in vast numbers and when they bloom, what buds from the polyp are baby jellyfish. They even have a primitive nervous
system with a ‘brain’ that is in fact a network of nerve cells, that allows it to sense their environments, such as changes in water chemistry or the touch of another animal.
When some species of medusa
like the immortal jellyfish (Turritopsis dohrnii) die, it sinks to the ocean floor and begins to decay. Amazingly, its cells then reaggregate, not into a new medusa, but into polyps, and from these polyps emerge new jellyfish. The jellyfish has thus
skipped to an earlier life stage to begin again. Its cells change from one type to another, producing a completely different body plan. So in fact we have a completely new jelly entering the watery world.
This of course
leads to the intriguing question if the human race could profit from this principle: would perhaps a few jelly genes in our gene pool enable us to regenerate whenever we are tired of ourselves?