Tardigrades are tiny, nearly translucent aquatic animals, found all over the world. Tardigrades are commonly known as water bears.
These little creatures – 0.2–1.2 mm long, 0.5 mm on average – may live for up to 60 years. Terrestrial species live inside the dampness of moss, lichen, leaf litter, and soil. Others are found in fresh or saltwater.
Water bears have a well-defined head and 4 pairs of legs which are fitted with claws. The legs are used for grasping and slow-motion acrobatics, not walking. Tardigrades are encased in a rugged but flexible cuticle which is periodically shed as the creature grows.
Water bears arose over 600 million years ago, after nematodes, but well before arthropods – some of which, such as insects, shed exoskeletons. Tardigrades are a distinctive branch on the tree of life.
Water bears have a physiology like larger animals, with muscles, a complete digestive system, a brain, and a nervous system.
With their mouth stilettos, some tardigrades perforate plants and absorb the sugary products of photosynthesis. Others suck the cellular contents of microorganisms or consume microbes whole.
The tardigrade body cavity is an open hemocoel that touches every cell. This affords efficient gas exchange and nutrition without the need for circulatory or respiratory systems. It is an elegantly efficient design.
Water bears generally have separate sexes and reproduce by eggs, but there are also hermaphrodites and parthenogenetic species. Fertilization is external.
Tardigrade development is direct, lacking larval stages. Water bears are born with their full complement of adult cells. Instead of cell division, water bears grow to adult size by their cells enlarging (hypertrophy). Tardigrades are eutelic: growing only by increasing the size of their cells, as the number of cells remains constant upon reaching maturity.
Through the ages, the wind carried water bears around the globe, where they adapted to niches with different environmental extremities. There are now over 1,100 species.
Tardigrades are tough. They have been subjected to temperatures as frigid as –272 Cº, or as hot as 150 Cº (well above water’s boiling point) and were able to revive after amenable conditions returned. Water bears can bear extreme pressure, suffocating gases, and seriously salty water.
Tardigrades survive extreme conditions via miraculous adaptations that allow cryptobiosis: suspended animation. Tardigrade tissue can withstand freezing crystallization, desiccation, and even the rigors of space. Water bears are inexplicably able to repair DNA damaged by radiation.
“Tardigrades are as close to indestructible as it gets.” ~ Brazilian physicist and astrobiologist Rafael Alves Batista
In going into suspended animation, tardigrades must dry out slowly to survive. In preparation, a water bear curls into a ball, termed a tun. German biologist H. Baumann called the tardigrade dry husk a Tönnchenform in 1922, but it is now commonly known as a tun.
“When a typical cell dries out, its membranes rupture and leak, and its proteins unfold and aggregate together, making them useless. DNA will also start to fragment the longer it is dry. Water bears survive drying with tricks for preventing and fixing the damage that cells like ours would die from.” ~ American biologist Thomas Boothby
To assist in preventing cell death, tardigrades synthesize trehalose: a sugar substitute for water, which lets cell structures and membranes remain intact when desiccated. Further, water bears have a unique genetic ability to create proteins which preserve cells during desiccation. These proteins encapsulate the molecular components of cells in glasslike matrices to preserve them, keeping them intact. Adding water melts the preservative proteins and sugars, allowing cellular revitalization.
Tardigrades rehydrate and return to activity within a few minutes to a few hours. A tun may be dormant for decades and come back to life.
Other organisms can reconstitute themselves from lifeless matter. The well-studied microscopic roundworm Caenorhabditis elegans can be frozen for decades, and yet, within minutes of thawing in a drop of warm water, again begin squirming, eating, and reproducing as if nothing had happened. Siberian roundworms, frozen for 42,000 years, were thawed out and came back to life.
We all know the term suspended animation. If life is merely matter, suspended animation could only be science fiction. Instead, suspended animation is a well-known scientific fact; one of many which disprove matterism.
Desiccated tardigrades, frozen nematodes, and spores and seeds all illustrate vitalism: that a certain energy gyre is the fundamental life force. Vitalism is an aspect of energyism.
For more on the wonders of Nature, read Unraveling Reality: Behind the Veil of Existence.