Arachnids
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Arachnida
Orders
Acarina Amblypygi Araneae Opiliones Palpigradi Pseudoscorpionida Ricinulei Schizomida Scorpiones Solifugae Uropygi

The arachnids, Arachnida, are a class of invertebrate animals in the subphylum Chelicerata. Arachnids are named for the mythological figure Arachne. They are chiefly terrestrial arthropods, some 65,000 to 73,000 species including the spiders, scorpions, harvestmen, ticks, and mites. The arachnids are easily distinguished from the insects by the fact that they have eight legs instead of six. The pedipalpi (leg-like mouthparts) of some species has instead been adapted for sensory, prey capture or reproductive functions. In solpugids the palpi are quite leg-like and make solpugids appear to have ten legs. Larval mites have only six legs: they grow their fourth pair when they molt into nymphs.

Arachnids are mostly carnivorous, feeding on the pre-digested body of insects and other small animals. Many are venomous - they secrete poison from specialized glands to kill prey or enemies. Others are parasites, some of which are carriers of disease. Arachnids usually lay eggs, which hatch into immature adults.

Orders

• Amblypygi - "Blunt rump" tailless whip scorpions with front legs modified into whip-like sensory structures as long as 25 cm or more
• Araneae - Spiders (40,000 species)
• Opiliones - Phalangids, harvestmen or daddy longlegs (4,500 species)
• Palpigradi - Microwhip scorpions
• Pseudoscorpionida - Pseudoscorpions
• Ricinulei - Ricinuleids, Hooded tickspiders
• Schizomida - "Split middle" whip scorpions with divided exoskeletons
• Scorpiones - Scorpions (2,000 species)
• Solifugae - Solipugids; wind scorpions, sun spiders or camel spiders (900 species)
• Uropygi - whip scorpions, with first legs modified as whip-like sensory organs and with a long thin tail at end of abdomen (60 species)
• Acarina - Mites and ticks (30,000 species)
  • Acariformes
    • Sarcoptiformes
    • Trombidiformes
  • Opilioacariformes
  • Parasitiformes - Holothyrans, ticks and mesostigmatic mites

Also see the following articles for links to species by common name:

• List of scorpion common names
• List of spider common names
• List of false scorpions

External links

• Arachnid Photo Gallery (http://www.americanarachnology.org/gallery_entrance.html) (The American Arachnological Society)
• International Society for Arachnology (http://www.arachnology.org)

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