| For my project on invertebrates, I chose to study tardigrades. |
| These are microscopic, or to be more precise, near-microscopic animals. |
| There are well over a thousand known species of these tiny animals, |
| which belong to the phylum Tardigrada. |
| Most tardigrades range in length from 0.05 to 1 millimetre, |
| though the largest species can grow to be 1.2 millimetres in length. |
| They are also sometimes called 'water bears': |
| 'water' because that's where they thrive best, |
| and 'bear' because of the way they move. |
| 'Moss piglet' is another name for tardigrades |
| because of the way they look when viewed from the front. |
| They were first discovered in Germany in 1773 by Johann Goeze, |
| who coined the name Tardigrada. |
| As I say, there are many different species of tardigrade, |
| too many to describe here, but generally speaking, the different species share similar physical traits. |
| They have a body which is short, and also rounded, a bit like a barrel, |
| and the body comprises four segments. |
| Each segment has a pair of legs, |
| at the end of which are between four and eight sharp claws. |
| I should also say that some species don't have any claws; |
| what they have are discs, |
| and these work by means of suction. |
| They enable the tardigrade to cling on to surfaces or to grip its prey. |
| Within the body, there are no lungs, or any organs for breathing at all. |
| Instead, oxygen and also blood are transported in a fluid that fills the cavity of the body. |
| As far as the tardigrade's head is concerned, |
| the best way I can describe this is that it looks rather strange, a bit squashed even, |
| though many of the websites I looked at described its appearance as cute, |
| which isn't exactly very scientific. |
| The tardigrade's mouth is a kind of tube |
| that can open outwards to reveal teeth-like structures known as 'stylets'. |
| These are sharp enough to pierce plant or animal cells. |
| So, where are tardigrades found? |
| Well, they live in every part of the world, |
| in a variety of habitats: most commonly, on the bed of a lake, |
| or on many kinds of plants or in very wet environments. |
| There's been some interesting research which has found that tardigrades are capable of surviving radiation |
| and very high pressure, |
| and they're also able to withstand temperatures as cold as -200 degrees centigrade, |
| or highs of more than 148 degrees centigrade, |
| which is incredibly hot. |
| It has been said that tardigrades could survive long after human beings have been wiped out, |
| even in the event of an asteroid hitting the earth. |
| If conditions become too extreme and tardigrades are at risk of drying out, |
| they enter a state called cryptobiosis. |
| They curl into a ball, called a tun, |
| that's T-U-N- by retracting their head and legs, |
| and their metabolism drops to less than 1% of normal levels. |
| They can remain like this until they are re-introduced to water, |
| when they will come back to life in a matter of a few hours. |
| While in a state of cryptobiosis, tardigrades produce a protein that protects their DNA. |
| In 2016, scientists revived two tardigrades that had been tuns for more than 30 years. |
| There was a report that, in 1948, |
| a 120-year-old tun was revived, |
| but this experiment has never been repeated. |
| There are currently several tests taking place in space, |
| to determine how long tardigrades might be able to survive there. |
| I believe the record so far is 10 days. |
| So, erm, moving on. |
| In terms of their diet, tardigrades consume liquids in order to survive. |
| Although they have teeth, they don't use these for chewing. |
| They suck the juices from moss, or extract fluid from seaweed, |
| but some species prey on other tardigrades, |
| from other species or within their own. |
| I suppose this isn't surprising, given that tardigrades are mainly comprised of liquid and are coated with a type of gel. |
| Finally, I'd like to mention the conservation status of tardigrades. |
| It is estimated that they have been in existence for approximately half a billion years |
| and, in that time, they have survived five mass extinctions. |
| So, it will probably come as no surprise to you, |
| that tardigrades have not been evaluated by the International Union for Conservation of Nature |
| and are not on any endangered list. |
| Some researchers have described them as thriving. |
| Does anyone have any questions they'd like to ask? |