Overview

Tardigrades are microscopic, eight-legged invertebrates belonging to the phylum Tardigrada. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who referred to them as "Kleiner Wasserbär" (little water bear). In 1776, the Italian biologist Lazzaro Spallanzani named them Tardigrada, meaning 'slow walkers'. (en.wikipedia.org)

Morphology

Tardigrades typically measure between 0.3 to 0.5 millimeters in length. Their bodies are segmented into four parts, each bearing a pair of unjointed legs ending in claws or suction discs. The body is covered by a non-calcified cuticle that is periodically molted. They lack specialized respiratory and circulatory systems; instead, gas exchange occurs directly through their body surface, and nutrients are transported via the body cavity fluid. (britannica.com)

Habitat and Distribution

Tardigrades inhabit a wide range of environments across the globe, from deep-sea trenches to mountaintops, tropical rainforests, and polar regions. They are commonly found in moist habitats such as mosses, lichens, leaf litter, and soil. Some species are marine, residing in the spaces between sediment particles or on algae. (en.wikipedia.org)

Reproduction and Life Cycle

Tardigrades reproduce through both sexual and asexual means, including parthenogenesis. Females lay eggs, which may be deposited into the molted cuticle or directly into the environment. The eggs hatch into juveniles that resemble miniature adults, undergoing several molts before reaching maturity. (en.wikipedia.org)

Survival Mechanisms

One of the most remarkable features of tardigrades is their ability to enter a cryptobiotic state known as a "tun". In response to desiccation or other adverse conditions, they lose almost all body water, retract their legs, and form a desiccated, resistant form. In this state, their metabolism reduces to 0.01% of normal levels, allowing them to survive extreme temperatures ranging from -272°C to 150°C, high levels of radiation, the vacuum of space, and pressures up to 1,200 atmospheres. (britannica.com)

Genetic Adaptations

Recent studies have identified specific genes that contribute to tardigrades' resilience. For instance, the gene Dsup (damage suppressor) has been shown to protect their DNA from radiation-induced damage. Additionally, tardigrades produce unique proteins that form a glass-like matrix during desiccation, stabilizing their cellular components. (en.wikipedia.org)

Evolutionary History

Tardigrades are believed to have evolved over 500 million years ago, with fossil records dating back to the Cambrian period. They are considered to be closely related to arthropods and nematodes, sharing a common ancestor within the superphylum Ecdysozoa. (en.wikipedia.org)

Research and Applications

The extraordinary survival capabilities of tardigrades have made them subjects of extensive scientific research. Understanding their mechanisms of resilience has potential applications in fields such as medicine, biotechnology, and astrobiology. For example, insights into their desiccation tolerance could inform the development of better preservation techniques for biological materials. (en.wikipedia.org)