1For my project on invertebrates, I chose to study tardigrades.
2These are microscopic, or to be more precise, near-microscopic animals.
3There are well over a thousand known species of these tiny animals,
4which belong to the phylum Tardigrada.
5Most tardigrades range in length from 0.05 to 1 millimetre,
6though the largest species can grow to be 1.2 millimetres in length.
7They are also sometimes called 'water bears':
8'water' because that's where they thrive best,
9and 'bear' because of the way they move.
10'Moss piglet' is another name for tardigrades
11because of the way they look when viewed from the front.
12They were first discovered in Germany in 1773 by Johann Goeze,
13who coined the name Tardigrada.
14As I say, there are many different species of tardigrade,
15too many to describe here, but generally speaking, the different species share similar physical traits.
16They have a body which is short, and also rounded, a bit like a barrel,
17and the body comprises four segments.
18Each segment has a pair of legs,
19at the end of which are between four and eight sharp claws.
20I should also say that some species don't have any claws;
21what they have are discs,
22and these work by means of suction.
23They enable the tardigrade to cling on to surfaces or to grip its prey.
24Within the body, there are no lungs, or any organs for breathing at all.
25Instead, oxygen and also blood are transported in a fluid that fills the cavity of the body.
26As far as the tardigrade's head is concerned,
27the best way I can describe this is that it looks rather strange, a bit squashed even,
28though many of the websites I looked at described its appearance as cute,
29which isn't exactly very scientific.
30The tardigrade's mouth is a kind of tube
31that can open outwards to reveal teeth-like structures known as 'stylets'.
32These are sharp enough to pierce plant or animal cells.
33So, where are tardigrades found?
34Well, they live in every part of the world,
35in a variety of habitats: most commonly, on the bed of a lake,
36or on many kinds of plants or in very wet environments.
37There's been some interesting research which has found that tardigrades are capable of surviving radiation
38and very high pressure,
39and they're also able to withstand temperatures as cold as -200 degrees centigrade,
40or highs of more than 148 degrees centigrade,
41which is incredibly hot.
42It has been said that tardigrades could survive long after human beings have been wiped out,
43even in the event of an asteroid hitting the earth.
44If conditions become too extreme and tardigrades are at risk of drying out,
45they enter a state called cryptobiosis.
46They curl into a ball, called a tun,
47that's T-U-N- by retracting their head and legs,
48and their metabolism drops to less than 1% of normal levels.
49They can remain like this until they are re-introduced to water,
50when they will come back to life in a matter of a few hours.
51While in a state of cryptobiosis, tardigrades produce a protein that protects their DNA.
52In 2016, scientists revived two tardigrades that had been tuns for more than 30 years.
53There was a report that, in 1948,
54a 120-year-old tun was revived,
55but this experiment has never been repeated.
56There are currently several tests taking place in space,
57to determine how long tardigrades might be able to survive there.
58I believe the record so far is 10 days.
59So, erm, moving on.
60In terms of their diet, tardigrades consume liquids in order to survive.
61Although they have teeth, they don't use these for chewing.
62They suck the juices from moss, or extract fluid from seaweed,
63but some species prey on other tardigrades,
64from other species or within their own.
65I suppose this isn't surprising, given that tardigrades are mainly comprised of liquid and are coated with a type of gel.
66Finally, I'd like to mention the conservation status of tardigrades.
67It is estimated that they have been in existence for approximately half a billion years
68and, in that time, they have survived five mass extinctions.
69So, it will probably come as no surprise to you,
70that tardigrades have not been evaluated by the International Union for Conservation of Nature
71and are not on any endangered list.
72Some researchers have described them as thriving.
73Does anyone have any questions they'd like to ask?