Arachnid
Acarina
Amblypygi
Araneae
Opiliones
Palpigradi
Pseudoscorpionida
Ricinulei
Schizomida
Scorpiones
Solifugae
Uropygi
</table>
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:
