Phylum Tardigrada Summary:

Phylum Tardigrada Summary:

A. Tardigrades and Gummy Bears

Tardigrades have been compared to gummy bears because:

1. they come in a variety of colors

2. have a gummy outside

3. look like miniature bears

B. Walks like a bear, looks like a bear, must be a bear...not exactly.

Tardigrade characterisitics:

1. have bilateral symmetry

2. body length of 0.5-1.2 mm

3. look like miniature bears in motion

4. they cling and waddle through substrate

5. have no circulatory or respiratory system

6. breathe throught their skin

7. body is divided into segments

8. have weel developed muscles

9. entire body acts as a pump for fluids within

10. their wide variety of colors could come from the pigments within their cuticle, left overs from what they ate, and internal body fluids

11. they may be armored or not

12. they have two piercing stylets in which they pierce their prey's cells with to suck their juices out with their buccal apparatus.

13. Pharnyx acts as a pump to suck the juices in.

14. They eat plants, small worms, nematodes, fungi, and other tardigrades.

15. they molt their cuticle

16. have eyespots

17. have four sets of unjointed legs with claws at the the end of them

18. body has more then two cell layers.

19. body has a fixed number of cells ( Eutelic)

20. Body growth is by cell size and not by number

21. reproduction normall sexual and gonochoristic, but can be

parthenogenetic

C. Water bears back claws function.

1. back legs placed further back and out from the other set of three.

2. grasping objects

3. gaining distance

D. Reproduction and Embryology

1. Parthenogenesis

2. Sexual

a. females lay eggs in the exuvium as they molt, after which males ejaculate spermatozoa in the old cuticle

b. as a female is molting, males may introduce spermatozoa into the gonopore or cloaca. The spermatozoa travel up the oviduct into the ovary

where fertilization occurs.

3. Cleavage is total and equal

4. Tardigrades use their claws to break out of the ornamental egg.

E. Tardigrades and Arthropods

1. Believe they sit close to one another on evolutionary tree

2. DNA evidence

a. Phylogentic analysis confirms that tardigrades are associated with arthropods, and that 18S rRNA gene phylogeny is consisitent with the morphology-based hypothesis of tardigrade evolutionary relationships.

F. So what makes a Tardigrade a Tardigrade?

1. Cryptobiosis- the way tardigrades have been able to manipulate themselves to be able to survive under all sorts of enviromental stress.

a. it is a truly death-like state

b. metabolism is lowered to less than 0.01% of normal, and body water is decreased to less than 1%

c. cryptobiotic methods:

1. Anoxybiosis- a bloated stage in reaction to a lack of oxygen in their environment. They can float around until conditons become better for about two-four days.

2. Anhydrobiosis- reaction to a loss of water within their enviroment. They go into a tun stage, which looks similar to a cocoon. The sugar Trehelose triggers this reaction, in which the tardigrades muscles contract, their legs are pulled in, and their body forms a tight ball. They can like this for a long time, and will return to normal when water is returned to their environment.

3. Cryobiosis- another tun stage, but as a result to freezing. Tardigrades can withstand below freezing temperatures due to the tun stage.

4. Osmobiosis- another tun stage as a result of increased salinity in their environment.

D. when tardigrades are in tun they are resistant to the following conditions;

1. x-rays of 570,000 roentgens ( 500 is lethal to humans)

2. Vaccums like outer space

3. boiling alcohol

4. pressures six times greater then the deepest oceans.

E. Tardigrades ARE NOT extremeophiles!

1. they are not adapted to live in extreme environments, instead they can merely survive those conditions. The longer the exposure the more of their chance of dying.

G. Where are Tardigrades found?

1. Everywhere

http://www.microscopy-uk.org.uk/mag/artmay99/dwbear.html

this website has more information about where to find them

2. where ever there is moss or leaf litter , you may have a chance of finding a water bear. They live within the tiny water droplets of the moss, and that is how they got their name.

3. due to their ability to survive extreme conditions, they have been spotted everywhere on the planet.

H. Why aren't they studied more?

1. size

2. trained eye and patience is needed

I. Interesting research concerning water bears and you

1. scientists are trying to harness the sugar Trehelose, the sugar that makes the water bear go into tun , and if they are successful, they may be able to apply to organ transplants.

a. they applied to a rat's heart, and let it sit for ten days in a "tun" stage. Ten days later, they were able to make it beat again. Right now, the human heart can only withstand being out of the body for four hours.

b. application for space travel

c. hypothesis of what life looks like on other planets (extreme animals remember)

J. References:

Garey, James R. 2003. Tardigrade Phylogeny: congruency of Morphological and Molecular Evidence

Elsberry, Wesley. 1982. Phylum Tardigrada.

Nickel, Kenneth. 2003. Collecting and Preserving Tardigrades

Miller, William. 1997. Tardigrades: Bears of the Moss.

Kinchin, Ian M. The Biology of the Tardigrades.

Pechenik, Jan A. 2000. Biology of the Invertebraes. pp. 400-401

Zoology. McGraw-Hill Book Company. pp. 106, 153-154.

Marine Invertebraes of the Pacific Northwest. pp. 296.

Mach, Martin. The Incredible Water Bear.