Tardigrades (Phylum Tardigrada, Superphylum Ecdysozoa) Polyextremophiles

Tardigrade Biology Facts:

• Common Names - water bears or moss piglets.
• Phylum Tardigrada, part of the superphylum Ecdysozoa.
• More than 1000 species have been identified.
• They are microscopic, water-dwelling, segmented animals with 8 legs (see image).
  
• Adults may grow to length 1.5 mm.
• Smallest adults can be below 0.1 mm.
• Larvae on hatching can be smaller than 0.05 mm.
• Locations - Himalayas to the deep sea (below 4,000 m) as well as equator to polar regions.
• Can be found on lichens & mosses.
• Most tardigrades are phytophagous (plant eaters), or bacteriophagous (bacteria eaters).
  

Tardigrade Anatomy:

• Have a body with four segments (this does include the head).
• Consist of 4 pairs of legs without joints.
• Have feet with claws or toes.
• Surface cuticle which contains chitin and is able to be moulted.
• Contain a ventral nervous system with one ganglion per segment.
• There is a multilobed brain.
• Tardigrades have rhabdomeric pigment-cup eyes.
• Have a haemocoel rather than a coelom (except around the gonad, coelomic pouch).
• They have a sucking type pharynx.
• Males & females are usually present, each with a single gonad.
• Some species are, however, parthenogenetic.

Polyextremophile Capabilities:

• Tardigrades are polyextremophiles - i.e. can survive in extreme environments that would kill almost any other animal.
• Some tardigrades can survive temperatures of -273°C, close to absolute zero. [1]
• Some can survive temperatures as high as 151 °C (303 °F).
• Can survive 1,000 times more radiation than other animals such as humans. [2]
• Have been described as going for almost a decade without water. [3]
• Some have even reported to survive the vacuum of outer space. [4]

Tardigrade History:

• Tardigrades were first described by Johann August Ephraim Goeze in 1773 (kleiner Wasserbär = little water bear).
• Name Tardigrada was given by Lazzaro Spallanzani in 1777 and means "slow walker".
• The name water bear comes from their gait - which looks like a bear walking.

Tardigrade Phylogeny:

• Recent sequencing data (DNA & RNA) suggest that tardigrades are related to the arthropods & Onychophora. [5]
• Considered in some schemes as Ecdysozoa.

References:
[1] - Becquerel P. (1950). "La suspension de la vie au dessous de 1/20 K absolu par demagnetization adiabatique de l’alun de fer dans le vide les plus eléve". C. R. hebd. Séances Acad. Sci. Paris 231: 261–263.
[2] - Radiation tolerance in the tardigrade Milnesium tardigradum
[3] - Crowe, John H.; Carpenter, John F.; Crowe, Lois M. (October 1998), "The role of vitrification in anhydrobiosis", Annual Review of Physiology 60: 73–103
[4] - K. Ingemar Jönsson, Elke Rabbow, Ralph O. Schill, Mats Harms-Ringdahl and Petra Rettberg (2008). "Tardigrades survive exposure to space in low Earth orbit". Current Biology 18 (17): R729–R731.
[5] - http://faculty.uml.edu/rhochberg/hochberglab/Courses/AdvancedInvertZool/Tardigrada/Tardigrade%20DNA%20Taxonomy.pdf

Image by Goldstein lab - tardigrades (cc)
Scanning electron micrograph of an adult water bear (tardigrade), Hypsibius dujardini.
by Bob Goldstein & Vicky Madden, UNC Chapel Hill tardigrades.bio.unc.edu/


Posted by ALCHEssMIST.
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