In today’s show, we will discuss four animals that are also extraordinary in terms of their ability to survive. They are also known as water bears, which comes from the way they walk. Aside from their tiny size and ubiquity, what stands out about tardigrades is their durability. The physiological response that enables tardigrades to be so tough is called cryptobiosis. It is a reversible suspension of metabolism that is achieved by different means, depending on the circumstances. A hundred years seems like a long time, but it is a blip in the life of the glass sponge. Glass sponges are sea sponges, but they’re different from other sponges and how their bodies are built. With a nod to the being’s regenerative ability, a very small freshwater invertebrate was given the same name. Biologists have discovered that hydras have an endless supply of three types of stem cells. These cells are biological raw materials, capable of continuous division and differentiation into any type of cell needed. Turritopsis dohrnii is a species of small jellyfish. When threatened by environmental stress or injured, they can revert to their infancy and start over again. They undergo a process called cellular transdifferentiation by which one type of cell is converted into another.