S3E2: Cnidaria
The Entangled Bank
Phylum: Cnidaria
December 06, 2019
Bighospitality.co.uk. “Are You Ready for This Jelly?” Bighospitality.co.uk, www.bighospitality.co.uk/Article/2017/11/16/Should-chefs-be-putting-jellyfish-on-their-menus.
Season 3 Episode 2: Cnidaria
Listen to Episode 2 on Stitcher!
Jellyfish are the squishy blobs of jelly in the ocean that we all know and love (or fear). But what are these colorful and even translucent creatures really? On this episode we’re tackling the phylum cnidaria. From diverse life cycles to immortality, we’re looking at what makes these creatures so unique.
Cnidaria
Mahalski, Bruce, and Heritage Te Manatu Taonga. “The Five Classes of Cnidarians.” Te Ara Encyclopedia of New Zealand – Te Ara Encyclopedia of New Zealand, Ministry for Culture and Heritage Te Manatu Taonga, 27 June 2019, teara.govt.nz/en/diagram/4722/the-five-classes-of-cnidarians.
A phylogenetic tree of the phylum cnidaria with the various classes.
Left to right, Scyphozoa, Cubozoa, and a colony of Hydrozoan polyps.
Cnidarians as a phylum have a few defining synapomorphies. To begin, the first trait is the nerve net. The nerve net runs all through a jellyfish, extending from their body, which is called a bell, down to their tentacles. Secondly, jellyfish take on two different body forms. These body forms are known as medusa, which is the free-swimming mature state, and bottom-dwelling polyps, which is the juvenile state (See Life Cycle below). Third, jellyfish have a structure called a rhopalia, which senses light, odor and orientation. Essentially, this structure functions as jellyfish eyes. And lastly, the pacemaker. The pacemaker is how a jellyfish moves. This structure controls expansion and contraction of their bodies, dictating speed and direction.
The Life Cycle
Smithsonian NMNH/The Ocean Portal Team. (n.d.). Jellyfish and Comb Jellies, Cnidaria and Ctenophora. Retrieved from Smithsonian, Ocean website: https://ocean.si.edu/ocean-life/invertebrates/jellyfish-and-comb-jellies#section_294
A summary of the life cycle found in cnidarians. The polyp stage represents the bottom-dwelling juvenile jellyfish, while the medusa stage (the adult jellyfish) is the free-swimming form.
Man-of-War
Bermuda Institute of Ocean Sciences. “Currents.” BIOS, www.bios.edu/currents/when-is-a-jellyfish-not-a-jellyfish.
A colony of polyps from the group Hydrozoa, phylum Cnidaria.
Cnidarians as a phylum have great diversity. From variation in separate sexes and internal or external fertilization, the various species of cnidaria have evolved unique life cycles despite their similarities. Even day-to-day life varies among the jellyfish, while some are primarily found in the medusa stage and others in colonies of polyps. These colonies are so large that they are mistaken as an individual organism (see The Man-of-War above). In the same group as the Man-of-War, the turritopsis dohrnii is found. This jellyfish has the ability to transdifferentiate, creating an immortal individual. Transdifferentiation allows for the jellyfish in the medusa stage to revert back to the polyp stage, essentially hitting the reset button in life.
Human Interactions
Chat, Jinho. “Jellyfish Polyp.” Flickr, Yahoo!, 29 Sept. 2011, www.flickr.com/photos/15914114@N03/6194621071.
A colony of polyps attached to the shell of a mussel.
While they’re in this polyp stage, the jellyfish nest onto structures found within their habitat. In nature this would be corals, but artificial structures such as those used for aquaculture, fishing and shipping industries can simulate their natural habitat. When they use man-made structures as habitats, it makes the populations of jellyfish much more visible to us as humans than they would be when using coral as habitats. Jellyfish populations are also experiencing increases from things like industrial overfishing, introduction of non-native species, and climate change, so there’s been increases of jellyfish blooms in areas with higher human disturbances.
Humans have a lot of misconceptions about jellyfish. They’re considered marine “pests” by beachgoers and most humans. Most people just know to avoid them if they see them in the water, which leads to a lack of education about jellyfish. The big concern most people have about jellyfish is in regard to the dangers that they pose. Many non-harmful species have evolved to have visual similarities to more harmful jellyfish that they share their locations with, so the best thing to do is to be aware of the species in your local areas or any areas you may visit. Not all jellyfish are harmful, but, being respectful of jellyfish and giving them space by staying away is recommended for all jellyfish types.
Ultimately, not a lot of research has been done on jellyfish. To fully understand these creatures, researchers need to analyze their diverse life-cycles in more depth. For example, transdifferentiation is a process researchers don’t fully understand, but has great potential for aging treatments in humans.
References
Baumann, S., & Schernewski, G. (2012). Occurrence and public perception of jellyfish along the German Baltic coastline. Journal of Coastal Conservation, 16(4), 555-566. Retrieved from http://www.jstor.org/stable/23327148
Cartwright, P., & Nawrocki, A. (2010). Character Evolution in Hydrozoa (phylum Cnidaria). Oxford Academic, 50(3). Retrieved from https://academic.oup.com/icb/article/50/3/456/620784
Duarte, C. M., Pitt, K. A., Lucas, C. H., Purcell, J. E., Robinson, K., Brotz, L., … Graham, W. M. (2013). Is global ocean sprawl a cause of jellyfish blooms? Frontiers in Ecology and the Environment, 11(2), 91–97. https://doi.org/10.1890/110246
Graham, W. M., Gelcich, S., Robinson, K. L., Duarte, C. M., Purcell, J. E., Madin, L. P., … Condon, R. H. (2014). Linking human well-being and jellyfish: ecosystem services, impacts, and societal responses. Frontiers in Ecology and the Environment, 12(9), 515–523.
Hasegawa, Y., Watanabe, T., Takazawa, M., Ohara, O., & Kubota, S. (2016). De Novo Assembly of the Transcriptome of Turritopsis, a Jellyfish That Repeatedly Rejuvenates. Zoological Science, 33, 366–371. Retrieved from https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/216317/1/zs150186.pd
Kubota, S., & Nagai, S. (2018). 16S Mitochondrial gene sequence analysis of some Turritopsis (Hydrozoa, Oceanidae) from Japan and Abroad, 14, 1–6. Retrieved from https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/230297/1/Kuroshio.Bio_14_1.pdf
Lisenkova, A. A., Grigorenko, A. P., Tyazhelova, T. V., Andreeva, T. V., Gusev, F. E., Manakhov, A. D., … Rogaev, E. I. (2017). Complete mitochondrial genome and evolutionary analysis of Turritopsis dohrnii, the “immortal” jellyfish with a reversible life-cycle. Molecular Phylogenetics and Evolution, 107, 232–238. https://doi.org/10.1016/j.ympev.2016.11.007
Martell, L., Piraino, S., Gravili, C., & Boero, F. (2016). Life cycle, morphology and medusa ontogenesis of Turritopsis dohrnii (Cnidaria: Hydrozoa). Italian Journal of Zoology, 83(3), 390–399. https://doi.org/10.1080/11250003.2016.1203034
Miglietta, M., & Lessios, H. (2008). A Silent Invasion. Springer Science+Business Media. Retrieved from https://repository.si.edu/bitstream/handle/10088/12067/stri_Miglietta_and_Lessios_2008.pdf
Miglietta, M. P., Maggioni, D., & Matsumoto, Y. (2018). Phylogenetics and species delimitation of two hydrozoa (phylum Cnidaria): Turritopsis (McCrady, 1857) and Pennaria (Goldfuss, 1820). Marine Biodiversity, 49(3), 1085–1100. doi: 10.1007/s12526-018-0891-8
Miglietta, M. P., Piraino, S., Kubota, S., & Schuchert, P. (2007). Species in the genus Turritopsis (Cnidaria, Hydrozoa): A molecular evaluation. Journal of Zoological Systematics and Evolutionary Research, 45(1), 11–19. https://doi.org/10.1111/j.1439-0469.2006.00379.x
Purcell, J. E. (2012). Jellyfish and Ctenophore Blooms Coincide with Human Proliferations and Environmental Perturbations. Annual Review of Marine Science, 4(1), 209–235. Retrieved from https://doi.org/10.1146/annurev-marine-120709-142751
Sahu, S., Dattani, A., & Aboobaker, A. A. (2017, October 1). Secrets from immortal worms: What can we learn about biological ageing from the planarian model system? Seminars in Cell and Developmental Biology. Elsevier Ltd. https://doi.org/10.1016/j.semcdb.2017.08.028
Satterlie, R. (2010). Do jellyfish have central nervous systems? The Journal of Experimental Biology, 1215–1223.
Sweetman, A. K., Smith, C. R., Dale, T., & Jones, D. O. B. (2014). Rapid scavenging of jellyfish carcasses reveals the importance of gelatinous material to. Proceedings: Biological Sciences, 281(1796), 1–8.
Sound Effect Links
Comments
Post a Comment