What are Tardigrades?

About Tardigrades:

• Tardigrades, often called water bears or moss piglets, are microscopic eight-legged animals.
• They are free-living tiny invertebrates belonging to the phylum Tardigrada.
• Around 1,300 species of tardigrades are found worldwide.
• Habitat:
  • Considered aquatic because they require a thin layer of water around their bodies to prevent dehydration, they’ve also been observed in all kinds of environments, from the deep sea to sand dunes.
  • Freshwater mosses and lichens are their preferred habitat, hence their nickname, moss piglet.
• They belong to an elite category of animals known as extremophiles, or critters that can survive extreme environments.
  • They can survive punishing heat, freezing cold, ultraviolet radiation, and even outer space.
  • Under unfavourable conditions, they go into a state of suspended animation called the “tun” state—in which the body dries out and appears as a lifeless ball (or tun).
  • Tardigrades can survive as tuns for years, or even decades.
• Physical Features:
  • Tardigrades are short, plump, and covered in a tough cuticle (similar to that of grasshoppers and other insects) that they must shed to grow.
  • Tardigrades are mostly about 1 mm (0.04 inch) or less in size. 
  • Their tiny bodies contain no bones and are instead supported by a hydrostatic skeleton – a fluid-filled compartment known as a hemolymph.
  • They have four pairs of legs, with 4-6 claws on each foot.
  • Their specialised mouthpart–called a bucco pharyngeal apparatus–allows them to suck the nutrients out of plants and other microorganisms.

Q1: What are invertebrates?

Invertebrate is any animal that lacks a vertebral column, or backbone, in contrast to the cartilaginous or bony vertebrates. More than 90 percent of all living animal species are invertebrates. Worldwide in distribution, they include animals as diverse as sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails, clams, and squid.

Source: 1st tardigrade fossils ever discovered hint at how they survived Earth's biggest mass extinction