What are tardigrades?

Answer 1

Tardigrades (Waterbears) are a phylum of invertebrate animals, belonging to the articulata and containing app. 750 species. They are a sister group to arthropoda, though some aspects remind to nematods. Tardigrades are quite small meiofaunal animals, the body length ranges between 0.08 mm and 1.5 mm. They have usually four pair of legs (in some species a reduction occurs) and a nervous system with ventral ganglia and a lobed brain. The body is covered with a cuticle that is shed several times during development . The cuticle is chitinous. There is no metamorphosis, though young tardigrades may look slightly different to adults. Tardigrades are oviparous. Some species are facultative parthenogenic, some may be obligatoric parthenogenetic. The fertilization may be internal or external. Tardigrades occur in quite different, also very extreme - environments, from deep sea to the highest mountains, from the tropic to the arctic and antarctic. All Tardigrades are bound to water (marine or fresh water) for active life. They also live on mossy place. Some groups are able to dry up to a cryptobiosis, thus withstanding extreme dryness, heat, deep temperatures (<30 K!) and radiation. During active life they are vulnerable by radiation, as shown by Josh Middleton.