An in-depth look at the genome of the moon jelly, Aurelia aurita, shows that it uses a common set of genes to transition between polyp and swimming life stages. Jellyfish undergo an amazing metamorphosis, from tiny polyps growing on the seafloor to swimming medusae with stinging tentacles. This shape-shifting has served them well, shepherding jellyfish through more than million years of mass extinctions on Earth.
The first in-depth look at the genome of a jellyfish—the moon jelly Aurelia aurita —reveals the origins of this successful survival strategy. The Aurelia genome, published online Dec. The results suggest animals can radiate into new niches and forms fairly easily. The research team was led equally by Gold, who performed much of the work as a postdoctoral fellow at the California Institute of Technology, and by Takeo Katsuki, a former project scientist at the Kavli Institute for Brain and Mind at UC San Diego and currently an application specialist at Thorlabs Japan Inc.
The hydrozoan Turritopsis dohrnii , an animal about 4. It has been dubbed the immortal jellyfish. 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 then settles on the seafloor as a blob-like cyst. Over the next hours , this blob develops into a new polyp - the jellyfish's previous life stage - and after maturing, medusae bud off.
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. The process behind the jellyfish's remarkable transformation is called transdifferentiation and is extremely rare. Medusa cells and polyp cells are different - some cells and organs only occur in the polyp, others only in the adult jellyfish. 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.
They can then mature again from there as normal, producing new, genetically identical medusae. This life cycle reversal can be repeated, and in perfect conditions, it may be that these jellyfish would never die of old age.
Turritopsis is a genus of tiny, translucent jellyfish. The species T. It was years later, in the s, that their immortality was accidentally discovered. Students Christian Sommer and Giorgio Bavestrello collected Turritopsis polyps, which they kept and monitored until medusae were released.
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. 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.
The discovery , aided by the spectacular nickname 'immortal jellyfish', captured the world's attention. For example, jellyfish, including immortal ones, are prey to other animals, such as fish and turtles. Polyps are also practically defenceless to predation by animals such as sea slugs and crustaceans.
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. 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. This is Turritopsis rubra, a jellyfish that is very closely related to T. The U. National Science Foundation propels the nation forward by advancing fundamental research in all fields of science and engineering. NSF supports research and people by providing facilities, instruments and funding to support their ingenuity and sustain the U.
Each year, NSF receives more than 40, competitive proposals and makes about 11, new awards. Those awards include support for cooperative research with industry, Arctic and Antarctic research and operations, and U. Get News Updates by Email. Connect with us online NSF website: nsf. Approximate positions of locality in Utah yielding fossil jellyfishes and the site of the famous Burgess Shale are marked as indicated.
Map derived using [41]. The new fossils come from an interval approximately 41—48 meters above the base of the Marjum Formation [26] , [27] ; approximate ages of some stratigraphic horizons are shown. Five specimens, UU [University of Utah] In these specimens, the umbrella widths are greater than the umbrella heights, with a maximum width of 8.
Further, there are at least twelve solid tentacles, 3. The tentacles appear to arise on the exumbrella at some distance from the umbrellar margin. Due to the limited number of preserved characters it is difficult to determine how these specimens should be classified within Medusozoa. However, members of the hydrozoan family Narcomedusae do possess similar relative umbrella dimensions and have tentacle insertions above the umbrellar margin, suggesting that UU Specimen UU Two other specimens, UU The specimen in Figure 5 is interpreted as a subumbrellar view of a jellyfish showing 18 pairs of radially arranged muscles; muscles are shown in a close-up view in Figure 6.
These muscles are similar to the swimming musculature in an extant order of scyphozoans, the Semaeostomeae, which is arranged as a continuous coronal muscle interrupted by radial folds of the gastric cavity [29]. The outer margin of the umbrella in UU This specimen displays three horseshoe shaped structures Fig.
The presence and arrangement of the swimming musculature and the possible presence of folded gonads are consistent with an assignment of these jellyfish to the scyphozoan order Semaeostomae, but given the uncertainties in preservation this assignment is made tentatively.
Another cnidarian specimen, UU For instance, it appears to have a dome-shaped umbrella, with a maximum height of 7. There also appears to be a deep groove encircling the basal third of the exumbrellar surface which, due to its position on the umbrella relative to the tentacles, bears a resemblance to a coronal groove, a feature common to the scyphozoan order Coronatae. Distal to the umbrellar margin there appears to be at least six pointed lappets approximately 1.
The apparent shape of the bell, presence of probable pointed lappets, relative position of the tentacles to these lappets, and the presence of a coronal groove are all characteristics of the scyphozoan order Coronatae, but the lack of additional specimens makes it difficult to assign this specimen conclusively to that taxon. Structure marked Cg in drawing interpreted as a coronal groove; structures marked L interpreted as lappets; structures marked T interpreted as tentacles.
Finally, two other specimens, UU There are thickenings at the proximal ends of the tentacles that are interpreted as pedalia. These pedalia are 2. Each pedalium has one tentacle associated with it. The specimen in Figure 10 appears to display a central cluster of three pedalia and tentacles with two other clusters on either side. Tentacles have a maximum length of 5. Many cnidarians, including cubozoans, have nematocysts arranged in transverse rows or lines in the outer tissue of the tentacles and these form circumferential bands of nematocyst batteries [30].
These transverse nematocyst batteries are particularly evident in contracted tentacles [31]. It is true that fossil ctenophores also feature transverse lines that represent ctenes of comb rows [32]. However, the material illustrated here differs from ctenophore comb rows because there is a clear outer margin outlining the tentacles: this is absent in comb rows. In addition, the tentacles in the specimens reported here hang below the umbrellar margin Figs.
Structures marked Ped in drawing are interpreted as pedalia. Structures marked Nb in drawing are interpreted as nematocyst batteries. The square shape of the umbrella, the presence of pedalia, tentacles, and nematocyst batteries, as well as the arrangement of the tentacles around the umbrellar margin in specimens UU We acknowledge that among the aforementioned traits umbrellar shape is most likely to be governed by taphonomic preservation; still, even setting this trait aside, in total these specimens show strongest affinities to this class of cnidarian jellyfish.
The more than 30 extant species of Cubozoa [34] belong to two families: Carybdeidae, characterized by simple pedalia, each with one tentacle; and Chirodropidae, characterized by branched pedalia, each branch with its own tentacle. The new fossil material shows more traits in common with the Carybdeidae because the pedalia are simple and unbranched.
However, given that taphonomic factors including incomplete preservation and orientation to bedding could influence the geometry of these structures, it is not possible to demonstrate conclusively that this material is referable to the Carybdeidae or even the Cubozoa.
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