Intro Bio

From My World To Yours

Structure & Function of the Tardigrade

Although tardigrades’ (phylum tardigrada) survival mechanisms prove to be far more resilient than that of any other life form, deeming it the “toughest animal on the planet,” they do share striking similarities with human beings. In regards to the digestive system between humans and tardigrades, naturally, the structure is incredibly different, but the physiology is fairly analogous. The digestive system of a tardigrade is comprised of six structures: the mouth, pharynx, esophagus, stomach, rectum, and anus – all of which are also present in a human being’s digestive system. However, this is where the majority of the commonalities between these two animals comes to a halt. Each individual structure of this invertebrate is unique only to the tardigrade. A tardigrade mouth, otherwise known as its buccal, is spear-like and contains two “stylets” that act as fangs, which are used to attach to lichens or moss or pierce their prey given tardigrades are omnivorous. Within the buccal region is a tongue that extracts nutrients and fluids from its food (Mullen, 2002) (Hamilton, 2014). Once the food enters the buccal, digestion begins as saliva breaks down the components. The food then enters the pharynx, which links the mouth to the esophagus. The pharynx is arranged into micro- and macroplacoids, which are calcified structures used for chewing, breaking the food down even further into a liquid state (Mach, n.d.). Once passed through the pharynx, the liquid enters the esophagus where it is pushed into the stomach. Just as in humans, the function of the stomach is to draw nutrients from food by chemical reactions. Any remanence that is not of any nutritious value will pass through the rectum and be excreted via the anus. Given the tardigrade is incredibly miniscule, it does not need a system to circulate nutrients throughout its body; therefore, a circulatory system is absent in tardigrades. Instead, a fluid known as hemolymph is used to transport nutrients, much of which is derived from the food the tardigrade digests, throughout the body. By examining the structure of the digestive system, the tardigrade is able to transport food through various canals, each of which function to break down. However, when we take a step back and look at the bigger picture, we cannot help but ask ourselves how the tardigrade remains alive during its state of suspended animation, cryptobiosis, when living in unsuitable conditions for decades and maybe even centuries. The explanation lies in the tardigrades’ description as the “toughest animal on the planet” – one on the many survival mechanisms of the tardigrade is to lower its metabolism to a death-like 0.01% of normal (Mullen, 2002). What is even more fascinating is the tardigrade is able to revive itself within hours or even minutes of being exposed to water, which is its suitable habitat, despite having been deprived of it for countless years. I believe it reasonable to conclude tardigrades are living proof a little can go a long way.

SEM of pharynx & buccal of Tardigrade

Images taken from Das Bartierchen – Journal

References
Fox-Skelly, J. (2015, March 13). Tardigrades return from the dead. Retrieved from Earth : http://www.bbc.com/earth/story/20150313-the-toughest-animals-on-earth
Hamilton, A. (2014, Oct. 1). Tardigrades.
Mach, M. (n.d.). Ebay tardigrades (III). Retrieved from The Water Bear : http://www.baertierchen.de/wb_apr05.html
Mach, M. (n.d.). Milnesium tardigradum . Retrieved from The Water Bear : http://www.baertierchen.de/wb_milnesium.html
Miller, W. R. (1997). Volume 43 Number 3. In W. R. Miller, Tardigrades: Bears of the Moss. Emporia: Emporia State University. Retrieved from Emporia State University .
Mullen, L. (2002, Sept. 1). Extreme Animals . Retrieved from Astrobiology Magazine : https://www.astrobio.net/extreme-life/extreme-animals/

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