In nature, there is a unique creature, nicknamed the "water bear." Few people know (with the exception of zoologists and space specialists) who know people, it affects both its appearance and its vitality. The creature received its primary name for its apparent similarity to a candy or teddy bear. True, he has six legs, and it is difficult to call a “face” cute, but the rest is clearly seen. But the “water” bear, because it is an inhabitant of this environment, cannot live (in the literal sense of the word) without moisture.
Discovery story
There is reason to believe that slow-moving water bears were precisely those creatures that the creator of the microscope van Levenguk saw back in 1702. However, the first official discovery of these unique ones is in 1773, when they were described by German pastor Goetze. Stunned by their appearance, he gave them the name kleiner wasserbär, which translates from German as a small (tiny) water bear. Microscopic creatures were studied in more detail and described by the Italian biologist Lazzaro Spallanzani, and this happened in 1776. Due to the extremely slow mobility of animals, he named them il tardigrado, as a result of which the term Tardigrada, that is, tardigrades, became the official scientific name.
The structure of the water bear
The first thing worth noting when studying tardigrades is the size of the animal. There are about 960 species of sea bears, and their body size varies from 0.1 to one and a half millimeters. It is very difficult to consider even the largest individual without a microscope. Tardigrades belong to the class of invertebrates, have a glassy, translucent body, visually broken into 4 segments by constrictions. Due to the presence of chitinous shell and periodic molting of a water bear, it is sometimes compared with insects. Most species have four pairs of limbs, but one of the smallest "breeds", only a tenth of a millimeter long, is an exception: it is a tardigrades. Each paw ends with claws in the amount of 4-6 pieces. The last pair of legs is oriented back.
The “face” of the creature is very unusual and resembles a dust collector on a vacuum cleaner. The mouth is equipped with a kind of stilettos with which a water bear pierces the shell of food. These animals have a nervous, digestive, reproductive, and nervous systems, but lack the circulatory and respiratory systems. Instead of blood, the cavity of the whole body is occupied by a special fluid, and the tardigrades have skin breathing. They have additional organs of touch in the form of a pair of appendages, and, strangely enough, eyes, which are pigmented spots on the body in front, but not in the place that can be conditionally called the head.
The water bear has a color depending on the habitat. The hue can be in the color range orange - scarlet or olive - dark green.
Tardigrades are heterogeneous, but males are much rarer than ladies, therefore, numerous cases of parthenogenesis (reproduction in the absence of fertilization) have been recorded.
Tardigrades are distributed throughout the world from the tropics to the Arctic Circle. However, if they can choose, wet lichens and mosses are preferred. The distribution of the water bear is passive: individuals move due to the flow of water or wind, and are also carried on the feathers of birds and animal fur.
Power Features
Most tardigraded water bears mostly live off mosses, small algae and bacteria. Three oceanic species parasitize exclusively on mollusks, larger aquatic invertebrates and sea cucumbers. About one and a half dozen species of water bears are outright predators, the diet of which includes microorganisms and roundworms; such a tardigrader is dangerous even to her own brothers - cannibalism is an everyday affair for her.
Indestructible creature
Most of all, the water bear interested scientists with its survivability. These creatures are able to preserve their life and ability to reproduce in the widest temperature range - from absolute zero (-273 degrees) to unbearable heat of +150. They survive in an aggressive environment, for example, in a hydrogen sulfide atmosphere. Radiation for them is not an insurmountable barrier to survival: after irradiation with it at a dose of 570 thousand X-rays, half of the water bears survived. For reference: radiation of "only" 500 x-rays is fatal to humans. Moreover, surviving tardigrades could still give (and gave) offspring.
Space sustainability
Most of all, the scientific community was interested in the ability of Tardigrada to withstand space conditions. In 2008, a research team led by environmental Swede Ingmar Jonsson sent an experimental batch of tardigrades into orbit around the Earth. One group was placed in a vacuum, the second was simultaneously irradiated with radiation, two were subjected to intensive UV treatment. The subjects in outer space spent 10 days and were almost completely drained. However, upon returning to more favorable conditions, most of the microscopic creatures returned to life, while retaining the ability to reproduce.
Survival foundation
The ability due to which a water bear can tolerate such a wide range of adverse conditions is the ability to fall into suspended animation through controlled anhydrobiosis. In other words, the tardigrades dry themselves, leaving a negligible amount of water in their bodies. In order not to lose them, the tardigrades forms a kind of wax shell on the surface of the body. When dried, tardigrades activate additional protective functions: sugar molecules prevent the expansion of cells, the production of antioxidants that resist radiation and inhibit DNA destruction is launched. When water enters the environment, the body of tardigrades begins to absorb it, and all vital functions are restored.
Natural enemies of the water bear
Despite all the survivability, a water bear is by no means immortal. Successfully counteracting an unfavorable external factor, he is rather helpless against predators who are not averse to feeding on them. In addition to their relatives, tardigrades are attacked by rotifers, ticks, springtails, roundworms and earthworms, larvae of various insects and crayfish. Part of the tardigrades perishes, becoming the prey of a carnivorous mushroom: its hyphae are intertwined in loops in which, as a trap, a water bear is stuck, after which mushroom threads grow into it. In addition, there are mushrooms whose spores are attractive for tardigrades in food terms. However, once in the intestines of a water bear, spores germinate, using the animal as a nutrient medium.