TARDIGRADES The Cutest Animalcule
Kingdom: Animalia Phylum: Tardigrada
What Are Tardigrades?
Tardigrades were discovered in 1773 by a German pastor named Johann August Ephraim Goeze. Three years later, the Italian clergyman and scientist Lazzaro Spallanzani added water to sediment from a rain gutter and examined it under a microscope. He found a plethora of tiny creatures swimming around that looked liked tiny bears. In his book, Opuscoli do Fisica Animale, e Vegetsabile, he named them il Tardigrado, meaning "slow-stepper", because they moved so slowly (Fox-Skelly 2015)
Tardigrades average at about half of one millimeter in length and are made up of about 1,000 cells. They are often called “Water Bears” or “Moss Piglets” due to their appearance that could resemble either of these descriptions.
Tardigrades are divided into two classes, Eutardigrada and Heterotardigrada. Generally, the members of Eutardigrada have a smooth cuticle without plates, whereas the Heterotardigrada is enveloped by a cuticle that is armored with plates. (Miller 2018)
Anatomy
Inside these tiny beasts we find anatomy and physiology similar to that of larger animals, including a full alimentary canal and digestive system. Mouth parts and a sucking pharynx lead to an esophagus, stomach, intestine and anus. There are well-developed muscles but only a single gonad. Tardigrades have a dorsal brain atop a paired ventral nervous system composed of the nerve cord and the ganglion as seen above. The body cavity of tardigrades is an open hemocoel that touches every cell, allowing efficient nutrition and gas exchange with no need for circulatory or respiratory systems. (Miller 2018)
Discover Magazine
Andreas Schmidt-Rhaesa, Corinna Schulze and Ricardo Neves/Nikon Small World
Environment
There are many species of Tardigrades. They are divided into three main groups: Terrestrial, Marine, and Freshwater.
Terrestrial tardigrades have three main states of being: active, anoxybiosis, and cryptobiosis. The active state involves eating, growing, reproducing, movement, and the activities of daily living. Anoxybiosis occurs when oxygen availability is low. Tardigrades are very sensitive to oxygen tension. Prolonged asphyxia will derail the osmolarity controls that regulate the Tardigrade’s internal water content and cause the Tardigrade to “puff up” in an appearance similar to the Stay-Puft Marshmallow Man. They will “float” around in their medium until the environment dries out and they can resume their normal activity.
The second state of being for the Tardigrade is cryptobiosis, which is a reversible suspension of the metabolism that has been compared to the phoenix-like ability to die and resurrect. Extreme dessication paralyzes metabolic activity due to the absence of water. Terrestrial Tardigrades are known as “limnoterrestrial”, which means they live within a film of water found in their terrestrial habitats.
Moss and lichens provide a spongey habitat featuring many small water pockets, and similar to sponges, these habitats slowly dry out. The Tardigrade will dessicate and shrivel into a structure that is approximately 1/3 its original size. This even tinier body is called a tun. In the tun state, the Tardigrade is just about invincible. (Miller 2018)
Tardigrades in marine environments generally prefer to inhabit seaweed, while those in freshwater environments prefer mainly freshwater algae.
Nutrition
Tardigrades use their buccal apparatus to feed upon detritus, leaf litter, lichens, moss, and a variety of organisms, such as bacteria, algae, protozoans, and other microfauna. The buccal apparatus consists of the buccal tube, a pair of piercing stylets, and a muscular sucking pharynx. The gut often contains chloroplasts and other cell components of algae, mosses or lichens. There are a few larger species of terrestrial Tardigrades, such as Macrobiotus and Milnesium that have been observed preying on protozoans, nematodes, rotifers and smaller species of tardigrades, even ingesting the entire organism at once. Other interesting contents have been found inside the guts of these predacious tardigrades, including rotifer jaws, tardigrade claws and buccal apparati. Little is known of the specific feeding requirements of marine and freshwater species, other than the intake of seaweed and algae. (Nelson 2002)
Reproduction
Most terrestrial Tardigrades are parthenogenetic or self-fertilizing hermaphrodites, while marine and freshwater Tardigrades are generally dioecious. In species that reproduce sexually, both males and females have a single gonad located superiorly to the gut. Males have two sperm ducts that connect to a gonopore, which opens into the hindgut. Females have a single oviduct located in the hindgut alongside either one or two seminal receptacles.
Fertilization can be direct, with the male depositing sperm into the female’s seminal receptacle, or may be indirect. Indirect fertilization occurs when the male deposits sperm under the female’s cuticle. When the female molts, she lays fertilized eggs into her shed cuticle (Nelson 2002).
Special Qualities
Art by Gillian Poss, Pen and India Ink
Tardigrades are known for their amazing abilities to survive extreme conditions. These abilities are mainly reserved for terrestrial Tardigrades. Marine and freshwater tardigrades do not have as many adaptive characteristics because their environments are fairly stable. The extreme survival adaptations have evolved in direct response to rapidly changing terrestrial environments in damp flora such as moss and lichens because they are often subject to rapid drying and extreme weather (Miller 2018).
Scientists have found Tardigrades surviving in boiling hot springs and buried under ice high in the mountains. They can survive being frozen at -328 degrees Fahrenheit. In 2007, researchers exposed dehydrated Tardigrades to the vacuum and solar radiation of space for 10 full days. When these Tardigrades were returned to earth and rehydrated, “68 percent of those that were shielded from the radiation survived, and even a handful of those with no radiation protection came back to life and produced viable offspring.” (Stromberg 2012)
Some scientists and Tardigrade enthusiasts believe that they are equipped to deal with outer space because they are actually from other planets.
When a tardigrade has undergone cryobiosis, it seems likely that survival is conferred by the release or synthesis of cryoprotectants. These agents may manipulate tissue freezing temperature, slowing the process and allowing an orderly transition into cryobiosis, and they “may suppress the nucleation of ice crystals, resulting in an ice-crystal form that is favorable for subsequent revival with thawing.” (Fox-Skelly 2015).
When Tardigrades start to dry out, they take in an abundance of antioxidants. They take in vitamins such as vitamins C and E, which combat the oxidation process.
According to Fox-Skelly, “The tun state is key to tardigrades' ability to cope with being dried out” (Fox-Skelly 2015).
The antioxidants may explain the Tardigrade’s extreme abilities. If a Tardigrade stays in its dry tun state, it’s DNA does get damaged. After the resurrection, however, the Tardigrade’s innate ability to repair DNA restores it to an optimal state. (Fox-Skelly 2015)
The Tardigrade as a Spirit Animal
If the Tardigrade appears to you as a Spirit Animal it is time to examine what you are doing for survival, whether financial, physical, or emotional. As the Tardigrade is comfortable in most environments, it lends one the ability to be comfortable in whatever environment you find yourself, whether at a place of business or a home. The Tardigrade will help you navigate difficult terrain. In some cases, there may be a need to be still and wait for a better situation, illustrated by the Tardigrade when it resurrects itself from a period of forced hibernation. In this time of renewal, one may find themselves in a new home or a new job, or is better able to meet their physical and financial needs. Tardigrades are known for their slow movements. Slowing down the fast pace of life may be a key for the manifestation of one’s highest goals. Their predacious nature may be an indicator to stand your ground when needed. The message is clear when Tardigrade appears. Focus on survival.
Tardigrada in several languages (without non-English characters):
Czech: Zelvusky Danish/Norwegian: Bjornedyr Dutch: Beerdiertjes English: Tardigrades (or: water bears) French: Tardigrades (or: ours aquatiques) German: Bartierchen Hungarian: Medveallatkak Icelandic: Bessadyr Lithuanian: Letunai (or: vandens meskuciai) Polish: Niesporczaki (or: wodne niedzwiadki) Slovakian: Pomalki Slovenian: Počasniki Spanish: Tardigrados (or: osos de agua) Suomi (Finnish): Karhukaiset
(Nelson and Marley 2000)
Interesting Tardigrade Videos:
References:
Fox-Skelly, Tardigrades Return From the Dead. BBC Earth, March, 2015
http://www.bbc.com/earth/story/20150313-the-toughest-animals-on-earth
Miller, William Randolph. Tardigrades. American Scientist, 2018, Sigma Xi, The Scientific Research Honor Society.
https://www.americanscientist.org/article/tardigrades
Nelson, Diane. Current Status of the Tardigrada: Evolution and Ecology. Integrative and Comparative Biology, Volume 42, Issue 3, July 2002, Pages 652–659
Nelson, D.R. & Marley, N.J. The biology and ecology of lotic Tardigrada. Freshwater Biology, 44(1): 93-108. 2000.
Stromberg, Joseph. How Does the Tiny Waterbear Survive in Outer Space? Smithsonian.com, September 11th, 2012. https://www.smithsonianmag.com/science-nature/how-does-the-tiny-waterbear-survive-in-outer-space-30891298/
Other resources:
https://news.nationalgeographic.com/2017/07/tardigrades-water-bears-extinction-earth-science/
https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1365-2427.2000.00586.x
COPYRIGHT 2019 THE CURIOUS BIOLOGIST