Welcome back to the discussion on amazing animal abilities! In this article, the “immortal” sea jelly (Turritopsis dohrinii), lyrebirds (genus Menura), and sea cucumbers (class Holothuroidea) will be highlighted. If you haven’t done so already, be sure to read Part 1 of this series, where the axolotl (Ambystoma mexicanum), the peacock mantis shrimp (Odontodactylus scyllarus), tardigrades (phylum Tardigrada), and the common cuttlefish (Sepia officinalis) were explored.
The Immortal Sea Jelly
The immortal sea jelly (Turritopsis dohrinii) is a small cnidarian residing in the Mediterranean Sea that is on average about three to five millimeters long. They are a part of the Hydrozoa class, which includes about 3700 species of other cnidarians, like Portuguese man-o-wars, by-the-wind sailors, and blue buttons. The majority of hydrozoans are what is called colonial, meaning that individuals stick together to function as one large mass.
Sea jellies typically go through three main morphologically different stages: the larva (called a planula), the polyp (juvenile), and the medusa (adult). In its medusa stage, the immortal sea jelly can have up to 90 tentacles and a reddish stomach, but the majority of its body is entirely transparent. The immortal sea jelly creates a colony of itself when it is in its polyp stage, performing a type of asexual reproduction called budding. Budding is where new individuals are grown from a bud coming off the “parent” organism. It is important to note, however, that the immortal jelly can do both asexual and sexual reproduction. In its adult stage (medusa), eggs are fertilized and undergo the maturation process shown below. It is in the polyp stage that asexual reproduction occurs via budding.
The immortal sea jelly is known to be a biologically immortal animal. When the immortal sea jelly is starved or injured, it will fall to the sea floor, and will revert back from a medusa morphology to a polyp morphology. Once a polyp, it will restart the budding process to form new medusas in the span of a couple weeks. This allows for the sea jelly to never die (at least from old age). Watch this short video for a recap on this info!
This process occurs through what biologists call transdifferentiation. This is in essence “cell recycling”. It is when a cell that is specialized for a specific function (adult cell) can change its specialization for a new function (polyp). Other animals, apart from the immortal sea jelly, can also undergo transdifferentiation. Some examples are moon jellies (medusa to polyp) and newts (iris cells to eye lens cells). There are ongoing research efforts being made to further understand transdifferentiation and its potential application in the medical field, particularly with stem cell development.
Lyrebirds
Lyrebirds are two species (M. novaehollandiae and M. alberti) of ground dwelling birds from the genus Menura that are native to forests of southeast Australia. Their breeding season is from April to October, and these birds have an average lifespan of thirty years. They are part of the taxonomic order passeriformes, which is the order that all songbirds belong to. The superb lyrebird (Menura novaehollandiae) is larger and lighter-colored of the two species, and the males possess a long ornamental tail for mating displays. They are roughly one meter long, including the tail. The Albert's lyrebird (Menura alberti) is smaller, and is only found in southeast Queensland and northeast of New South Wales. In New South Wales, the Albert's lyrebird is classified as vulnerable.
Both species of lyrebirds are known for their complex mimicking abilities and their elaborate courtship displays. The males build mounds from dirt and loose vegetation, and spread their tail wings while performing a song and dance for up to 20 minutes.
Lyrebirds can mimic virtually any sound, including the songs of more than twenty different species of birds, and even the sounds of some neighboring mammal species. They are also known to mimic human sounds like chainsaws, camera shutters, or car alarms. Males use the mimicry during their courtship displays and rituals, and females use mimicry to defend territory. Check out this article to hear how well these lyrebirds mimic other birds through sound comparisons, and check out this video to see a superb lyrebird perform this incredibly complex courtship display.
Lyrebirds are able to mimic such a wide array of sounds due to a combination of exceptional hearing, memory, and control of their vocal organ called the syrinx. Unlike humans, which have a voice box in the throat through which sound passes and is shaped by the mouth, lyrebirds, like all songbirds, have a different mechanism for producing sound. Lyrebirds have a structure called a syrinx that sits right above the lungs, allowing for two sounds to be created at once.
The presence of the syrinx, coupled with great hearing and memory, is what allows lyrebirds to mimic sounds. There is also, however, a learning curve to great mimicry in lyrebirds: juvenile lyrebirds learn how to mimic by practicing different sounds. Lyrebirds have also been known to learn mimicked sounds from each other. For example, a lyrebird may learn the sound of a car alarm, or a certain species of bird, not from the actual source but from one of its conspecifics (members of its own species).
Sea Cucumbers
Sea cucumbers are a group of benthic (seafloor dwelling) echinoderms in the class Holothuroidea. The phylum echinodermata also includes animals like sea stars, brittle stars, and urchins. There are roughly 1,200 species of sea cucumbers, and they can be anywhere from three quarters of an inch to 10 feet long. They are found worldwide, most commonly on the seafloor in shallow regions of the ocean (with few in the deeper sea) and have a lifespan of five to ten years (depending on the species). Just like sea stars and urchins, they also have tube feet that help them move around, and they come in a variety of colors including red, brown, white, blue, and some are even bioluminescent.
Despite not having a brain nor true sensory organs, sea cucumbers have a fascinating way of reacting to danger. Instead of a nervous system, they have a nerve ring with a nerve net that allows them to detect certain tactile and chemical stimuli. When threatened by a predator, they have the ability to eject their internal organs as a way to distract the predator. This is called evisceration, and it is a form of autotomy (the deliberate detachment of a body part when threatened).
Other animals, for example lizards, can autotomize their tails. Amazingly, sea cucumbers can fully regenerate their ejected organs in about six weeks. Watch this video to learn more about this awesome ability. Similar to the regenerative abilities of the axolotl, or the transdifferentiation of immortal sea jelly cells, scientists are interested in the regenerative abilities of the sea cucumber, and hope to extract some medicinal applications from them.
Conclusion
There are currently almost nine million species of animals known to man, so as you can imagine, the discussion on animals is endless! The animal kingdom is full of amazing strategies for survival, and hopefully this article, along with Part 1, was able to open the door to some of these awesome animals and their abilities. As new knowledge is continually being discovered, it can hopefully facilitate and encourage appreciation and reverence for the world’s biodiversity.
Sources
Immortal Sea Jelly:
Lyrebirds
Sea Cucumbers
https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Sea-Cucumbers
https://www.nationalgeographic.com/animals/invertebrates/facts/sea-cucumbers
https://www.aquariumofpacific.org/onlinelearningcenter/species/johnsons_sea_cucumber
https://www.scienceandthesea.org/articles/201804/cool-cucumber-regrows-itself
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