Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda, Subphylum Chelicerata

Common name: chelicerates, arachnids

Chelicerata is a division within the Arthropoda, containing animals such as spiders, scorpions, harvestmen, mites and ticks. Like all arthropods, they have a segmented body and segmented limbs and a thick chitinous cuticle called an exoskeleton. Chelicerates have two body segments; a cephalothorax and an abdomen. They have no antennae, but have six pairs of appendages. The most anterior appendages are called the chelicerae and are normally modified into pincers or fangs. The following pair, the pedipalps, are also commonly modified. The posterior four pairs of appendages are normally used for walking. Other than the marine horseshoe crabs, the Chelicerata are found primarily in terrestrial environments worldwide. Around 8,000 described species are found in Australia, with approximately 80,000 recognised species worldwide. The only class within Chelicerata which is not entirely marine is the Arachnida. The arachnids are grouped into ten orders, the Scorpiones (scorpions), the Pseudoscorpiones (pseudoscorpions), the Araneae (spiders), the Amblypygi (whip-spiders), the Shizomida (schizomids), the Palpigradi (palpigrades), the Opiliones (harvestmen), and three groups of mites and ticks: Opilioacariformes, Acariformes and Parasitiformes.

Araneae - Idiomatta sp. male
Image credit: Mark Harvey � Western Australian Museum
used with permission

Araneae - Peacock spider
Image credit: Jurgen Otto
used under a Creative Commons Attribution-NonCommercial-NoDerivs license

Amblypygi - Charon (Charontidae) from the Kimberley

Amblypygi - Charonsp. (Charontidae) from the Kimberley
Image credit: Mark Harvey � Western Australian Museum
used with permission

Pseudoscorpiones
Image credit: � Sophie Harrison
used with permission

Opiliones - Triaenonychini
Image credit: Marshal Hedin
used under a Creative Commons Attribution-NonCommercial license

Scorpiones - Urodacus armatus
Image credit: Mark Harvey � Western Australian Museum
used with permission

Parasitiformes - Kangaroo tick
Image credit: Jean and Fred Hort
used under a Creative Commons Attribution-NonCommercial license

Acariformes - Velvet mite
Image credit: Jurgen Otto
used under a Creative Commons Attribution-NonCommercial-NoDerivs license

References and further information

ABRS Australian Faunal Directory: Chelicerata
Atlas of Living Australia: Chelicerata
Encyclopedia of Life: Chelicerata
Tree of Life: Arthropoda: Chelicerata

This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Australia License.