The Immortal Jellyfish

Introduction

Turritopsis dohrnii, also referred to as the 'immortal jellyfish' is an organism that is capable of reverting completely back to a sexually immature, colonial stage after reaching sexual maturity as a solitary animal. In other words, this jellyfish has the ability to skip fertilization and larval stages and go back to an earlier stage of development as a polyp after already developing into the medusa stage. Stress, danger in an environment, or physical harm are factors that can set this mechanism off causing the jellyfish medusae to fall to the ocean floor where it will transform back into a polyp. That being said, the only real known causes of this species death is disease and predation from other organisms or starvation and disease in the larval stage.

Where They Live and What They Eat

Turritopsis prefer warmer waters, although they have been spotted in colder waters as well. They are mostly found in the Caribbean Sea and the Mediterranean, but because of their size they are a rare animal to spot. Their diet is made up of plankton, fish eggs, and small molluscs.

General Characteristics

This species is actually very small in size and would be barely noticeable swimming in the ocean. They are generally only around 4 to 4.5mm tall and wide (0.18 inch) as an adult. Their most distinguishable morphological feature is their bright red stomach that is visible through their translucent body in the medusa stage. They are bell shaped like many other typical jellyfish and can have upwards to 80-90 tentacles as an adult. Their morphology is typical of other cnidarians with features such as the mesoglea (a layer separating tissues), a gastrovascular cavity (the cavity that serves for digestion and has a single opening for both the mouth and anus), tentacles with cnidocytes (stinging cells used for prey capture and defense), radial body symmetry, gonads that are formed in the epidermis, and a larval planula (a flat larvae) stage.

Life Cycle(s)

The average jellyfish life cycle is dimorphic that begins in a larva stage and has one polyp stage and one medusa stage. The immortal jellyfish, too, has these life cycle characteristics, however, they are capable of re-doing their life cycle over as many times that may be necessary. The typical jellyfish begins its life cycle as a free-swimming larva called a plaunla. These tiny flat larvae swim around until they eventually find where they want to settle down. Once settled, the planula give rise to a colony of polyps that are anchored to some type of substrate. The polyps grow until the time is just right for them to bud and pop off to become free swimming medusae; the jellyfish form that is more recognizable. From here, the jellyfish will grow and eventually become sexually mature. Jellyfish are gonochoric, which means there are males and there are females and they reproduce sexually. Females release their eggs into the water, and males release sperm into the water. After fertilization has externally occurred, a new planula is formed and the medusae jellies continue to grow older.

Where the immortal jellyfish differs, is that after (or even before) it has become sexually mature and reproduced, it can stop exactly where it's at, drop to the ocean floor and revert back to the polyp stage of development. These polyps will be identical to the medusa when grown and there's no energy spent on another larval stage. This process is capable due to having certain cell types and a mechanism named transdifferentiation. In transdifferentiation, cells are capable of transforming into other cell types. For the immortal jellyfish, this means that its adult medusa stage cells can convert back to polyp stage cells, thus the entire morphology of the animal changes. The jellyfish doesn't have to be at a certain place in its life cycle to be able to do this either, whenever stress of some sort occurs, the jellyfish can go back to a polyp stage and start its life over again.

References

Schmich, Jurgen, et al. “.” International Journal of Developmental Biology, UPV/EHU Press,

www.ijdb.ehu.es/web/paper/062152js/induction-of-reverse-development-in-two-marine-

hydrozoans.

American Museum of Natural History. “The Immortal Jellyfish.” AMNH, 4 May 2015,

www.amnh.org/explore/news-blogs/on-exhibit-posts/the-immortal-jellyfish/.

“Home.” Everlasting Life: the 'Immortal' Jellyfish, 3 June 2016, www.rsb.org.uk/news/158-biologist/features/1510-

everlasting-life-the-immortal-jellyfish.

Rich, Nathaniel. “Can a Jellyfish Unlock the Secret of Immortality?” The New York Times, 28 Nov. 2012

“Immortal Jellyfish: The Creature That Defies Death.” Immortal Jellyfish, immortal-jellyfish.com/.

Brown, Heather. "Home." Famous Scientists, www.famouscientists.org/facts-about-the-immortal-jellyfish/.