[01:10.74]For my project on invertebrates, I chose to study tardigrades.
[01:15.57]These are microscopic - or to
be more precise -- near-microscopic animals.
[01:20.70]There are well over a thousand known species
of these tiny animals, which belong to the phylum Tardigrada.
[01:28.27]Most tardigrades range in
length from 0.05 to 1milimetre, though the largest species can grow to be 1.2 millimetres in
length.
[01:40.46]They are also sometimes called ‘water bears’: water because that's where they thrive
best and 'bear” because of the way they move.
[01:49.51]Moss piglet is another name for tardigrades because of the way they look when viewed from the front.
[01:56.69]They were first discovered in Germany in 1773 by Johann Goeze, who coined the name Tardigrada.
[02:06.20]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.
[02:18.33]They have a body which is short, and also rounded – a bit like a barrel-and the body comprises four segments.
[02:27.65]Each segment has pair of legs, at the end of which are between four and eight sharp claws.
[02:34.88]I should also say that some species don't have any claws;
[02:39.41]what they have are discs, and
these work by means of suction.
[02:45.03]They enable the tardigrade to cling on to surfaces or to
grip its prey.
[02:50.73]Within the body, there are no lungs, or any organs for breathing at all.
[02:55.88]Instead,
oxygen and also blood are transported in a fluid that fills the cavity of the body.
[03:04.12]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.
[03:21.41]The tardigrade's mouth is a kind of tube that can open outwards to reveal teeth-like structures known as 'stylets'.
[03:30.32]These are sharp enough to pierce plant or animal cells.
[03:34.91]So where are tardigrades found?
[03:38.11]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.
[03:51.53]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.
[04:18.06]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.
[04:28.60]If conditions become too extreme and tardigrades are at risk of drying out, they enter a state called cryptobiosis.
[04:37.54]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 one percent of normal levels.
[04:50.17]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.
[04:57.99]While in a state of cryptobiosis, tardigrades produce a protein that protects their DNA.
[05:05.83]In 2016, scientists revived two tardigrades that had been tuns for more than 30 years.
[05:13.60]There was a report that,
in 1948, a 120-year-old tun was revived, but this experiment has never been repeated.
[05:24.03]There are currently several tests taking place in space, to determine how long tardigrades might be
able to survive there.
[05:33.19]I believe the record so far is 10 days.
[05:36.99]So, erm, moving on.
[05:39.21]In terms of their diet, tardigrades consume liquids in order to survive.
[05:45.93]Although they have teeth, they don't use these for chewing.
[05:50.07]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.
[06:02.19]I suppose this isn't surprising, given that tardigrades are mainly comprised of liquid and are coated with a type of gel.
[06:10.80]Finally, I'd like to mention the conservation status of tardigrades.
[06:16.07]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.
[06:26.88]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.
[06:40.02]Some researchers have described them as thriving.
[06:44.66]Does anyone have any questions they'd like to ask?
