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Arthropoda - Arthropods
 Arthro - joint, Pod - foot

Arthropods comprise around 80% of all described animal species, currently there are over 1 million described arthropod species.

They are one of the oldest animal groups with fossils as old as 555 million years. One of the best known of all fossils, Trilobites are Arthropods and were present in significant diversity 530 million years ago.

Arthropods are found everywhere on earth in every kind of habitat, they fly, swim, crawl, burrow, and live as external and internal parasites.

The combined mass of Arthropods is easily greater than that of all other animals combined. The total human mass on earth has been estimated at being similar to the world termite total, the figures for ants are up to twenty times greater (both are insects).

The combined biomass of a crustacean, Euphausia superba, the Antarctic krill is in the region of 500 million tonnes making it by mass, the most abundant single species on earth.

However you look at it, it is difficult not to be convinced that earth is the planet of the Arthropods, they are older than nearly other animal groups, more numerous and of much greater biomass. Wherever you go on earth, if there is an animal living there it will most likely be an Arthropod, if it is on land, it will probably be an insect, in the sea a crustacean.


A fossil Trilobite, Paraceraurus, an early Arthropod from the Ordovician period (480-440 Million years ago)
Volchow River area, Russia
picture used permission of Vassil
published under Creative Commons Attribution ShareAlike 3.0 Unported License

 Basic Features:
  • Exoskeleton made of chitin, which leads to a discontinuous pattern of growth (the animal grows into it, then it can't get bigger until the next stage)
  • Metamorphosis common
  • Segmented bodies, segments not always evident externally though
  • Jointed appendages used for feeding and locomotion
  • Gas exchange through gills, tracheae or book lungs
  • Nitrogenous excretion through gills or Malpighian tubules
  • Bilateral symmetry (one line of symmetry down the middle - like you)

 

Kingdom - Animalia
Phylum - Arthropoda
Classes:

  • Arachnida - spiders, scorpions, ticks, mites
  • Chilopoda - centipedes
  • Diplopoda - millipedes
  • Crustacea - crabs, lobsters, shrimps, woodlice, barnacles etc.
  • Insecta - beetles, butterflies, true flies, bugs etc.

 

 


Sally lightfoot crab, Graspus graspus
 A modern Arthropod from the Galapagos Islands

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