October Lesson - Biology- Phylum Tardigrada


                                                                Phylum Tardigrada

    Tardi-what?  Tardigrades (Latin for slow walker) are a part of the animal kingdom, with approximately 750 species.  All are aquatic and generally live not far from your front door.  The preferred habitat is moss of all types.  The common name for this little creature is the  “Water Bear” .  Generally considered in the Phylum of Arthropods, invertebrate (no backbone) between the Nematodes (roundworms) and the Arthropods (crustacean, insects, ticks, and mites).  They range in size on average between 0.20 mm to 0.70 mm in length.

    Tardigrades are found all over this planet from the Himalayas to the deepest oceans.

    Their bodies have five segments (parts linked together), four pairs of legs and feet (not like ours), a mouth, and eyes.  Their muscles are well developed, and they have a nervous system, a digestive tract, and an excretory system.


    In their mouths, Tardigrades have two built-in knives or stylets for slicing into their meal and a sucking pharynx to remove the juices from their meal.  Some Water Bears are predatory, but most prefer moss.  In some respect, they fall into the lower animal kingdom, as they breathe through their skin or cuticle, because they lack a respiratory system.  Their whole body acts as a pump to circulate fluids in their system.  Tardigrades exhibit both sexual asexual reproduction.


    So what’s so special about this little animal?  Simply stated, they are in a league of their own.  They are the toughest animals on this planet.  How so?  Consider these facts.  The Water Bear can withstand the following and survive:

1. Temperature variance between–272.9 degrees Celsius to 200 degrees Celsius

2. Immersion in baths of liquid nitrogen, pure alcohol, hydrogen sulfide, and various potent mineral acids

3. Exposure to Ultra Violet Radiation A, B, and C

4. Can withstand 1,000 times the lethal dose of X-ray radiation to humans

5. Survive 6,000 atmospheres and high vacuums

6. Carbon Dioxide and other poisonous gases

7. Remain in a sealed glass jar for 112 years.  Given a drop of water, it can return back to life.


    How does this little animal survive all of these feats?  Well, the Water Bear has the ability to desiccate (lose moisture) from its body (estimates to 98%).  It flushes the fluids from its body.  Once accomplished, it enters into a reversible state of metabolic suspension called Cryptobiosis (dormant or suspension).  This state of Cryptobiosis is triggered by the surrounding environment in which the Water Bear finds itself.  Once the fluids are evacuated from its body, it shrivels to about 1/3 of its original size, into a wrinkled  “tun”, resembling dried coffee.  It is now ready to defend itself from radical changes in the environment.


    If fluids freeze inside our bodies, ice crystals form.  And if you have ever looked at ice crystals under a microscope, you will observe that they have many sharp edges.  These edges are what cause damage to cellular structures and tissues.  Remember, fluids expand when frozen.  When humans suffer from frostbite, it is damage to cellular structure brought on by ice crystals and the expansion of these crystals.  Human tissue, severely and deeply damaged by frostbite, rarely recovers.  If the Water Bear did not have the ability to evacuate the fluids and was dipped into liquid nitrogen, this little creature would split open and shatter, if it were dropped onto a hard solid surface.


    Can you go hunting for Water Bears?  Absolutely!  All you need is access to a microscope with 40X, a piece of moss, distilled water, a flat dish, and a bear hunting you will go!  The colors of the Water Bear vary from red, red-orange, and orange to green.  Patience is important in order to find your first one.  After that, the rest will come easily.  You will not mistake the Water Bear’s gait; they simply resemble a bear walking.  Hence, the name Water Bear.


    If you wish to view the Water Bear under high magnification, do not position two slides directly together.  Place a barrier, such as Vaseline, between the slides.  The Water Bears can be harmed by crushing, (if they have not yet enter the Cryptobiosis state).  One suggestion is that you use incident light as opposed to through light from the microscope base.  A good strong flashlight works best.  This allows better control of the degree and the angle of light.


    So now you have some facts on this resilient and spectacular little animal.  Remember that as you study the Water Bear under the microscope, you are observing the toughest creature on this planet.  Isn’t nature marvelous?  I think so.