What is Arachnid?
{{Automatic taxobox | name = Arachnids | image = Arachnida collage (Update).jpg | image_upright = 1.3 | image_caption = '''Left to right''': ''[[Phidippus mystaceus]]'' ([[Araneae]]), [[Pseudoscorpion]] (Pseudoscorpiones), ''[[Hottentotta tamulus]]'' ([[Scorpiones]]), ''[[Ixodes ricinus]]'' ([[Ixodida]]), ''[[Heterophrynus]]'' ([[Amblypygi]]), ''[[Aceria anthocoptes]]'' ([[Trombidiformes]]), [[Harvestman]] (Opiliones), ''[[Galeodes|Galeodes caspius]]'' ([[Solifugae]]), and a [[Whip scorpion]] (Thelyphonidae). | fossil_range = {{Fossil range|435|0}}<small>[[Llandovery epoch|Early Silurian]] – [[Holocene|present]]</small> | taxon = Arachnida | authority = [[Lamarck]], 1801 | subdivision_ranks = Orders | subdivision = *[[Ricinulei]] * [[Opiliones]]&nbsp;– harvestmen * [[Solifugae]]&nbsp;– camel spiders * [[Acariformes]] mites * [[Parasitiformes]] mites and ticks * [[Pseudoscorpions|Pseudoscorpiones]]&nbsp;– pseudoscorpions * [[Scorpiones]]&nbsp;– scorpions * †[[Phalangiotarbi]] (extinct) * †[[Trigonotarbida]] (extinct) * †[[Uraraneida]] (extinct) * [[Spider|Araneae]]&nbsp;– spiders * †[[Haptopoda]] (extinct) * [[Amblypygi]]&nbsp;– whip spiders * [[Schizomida]]&nbsp;– short-tailed whipscorpions * [[Palpigradi]]&nbsp;– micro-whipscorpions * [[Thelyphonida]]&nbsp;– vinegaroons * ?[[Xiphosura]]&nbsp;– horseshoe crabs }} [[File:Spider-characteristics.png|thumb|right|230px|Basic characteristics of arachnids include four pairs of legs (1) and a body divided into two segments: the cephalothorax (2) and the abdomen (3).]] The '''arachnids''' are a [[Class (biology)|class]] of eight-legged [[arthropod]]s.<ref>Ruppert E.E. Fo, R.S. and Barnes R.D. 2004. ''Invertebrate zoology'' 7 ed, Brooks/Cole. p520 {{ISBN|0030259827}}.</ref> They are a highly successful group of mainly terrestrial [[invertebrate]]s: [[spider]]s,<ref>Foelix, Rainer F. 1996. ''Biology of spiders''. Oxford University Press. {{ISBN|0-19-509593-6}}.</ref> [[scorpion]]s, [[Opiliones|harvestmen]], [[tick]]s, and [[mite]]s, and a number of smaller groups.<ref>Sch