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Arachnida () is a class of joint-legged arthropods, in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.Adult arachnids have eight legs attached to the cephalothorax, although the frontmost pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ἀράχνη (aráchnē, ‘spider’), from the myth of the hubristic human weaver Arachne, who was turned into a spider.Almost all extant arachnids are terrestrial, living mainly on land. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 110,000 named species, of which 51,000 are species of spiders.
Arachnids, such as spiders and scorpions, have eight legs, in contrast to insects which have six legs. They also have two additional pairs of appendages adapted for feeding, defense, and sensory perception. Arachnids lack antennae and wings and have a body divided into two sections called the prosoma (cephalothorax) and opisthosoma (abdomen). They have an exoskeleton and internal structures like cartilage for muscle attachment. Arachnids have evolved various adaptations for terrestrial life, including respiratory systems like tracheae and book lungs, specialized appendages for locomotion, and excretory structures. They are mostly carnivorous, using venom to kill prey, and their digestive system is capable of rapidly breaking down and absorbing nutrients from prey. Arachnids have two types of eyes and other sensory organs like sensory hairs and slit sense organs. They reproduce using spermatophores and exhibit sexual dimorphism. Females usually provide parental care, although some species like scorpions and certain mites are viviparous or ovoviviparous.
Die Spinnentiere (Arachnida, eingedeutscht: Arachniden oder Arachnoiden; altgriechisch ἀράχνη aráchnē „Spinne“) sind eine Klasse der Gliederfüßer (Arthropoda) mit über 110.000 bekannten Arten. Gemeinsam mit den Pfeilschwanzkrebsen bilden sie den Unterstamm der Kieferklauenträger (Chelicerata). Zu den Spinnentieren gehören die Webspinnen, aber auch Weberknechte, Skorpione, Pseudoskorpione und Milben (inklusive Zecken).
Der Artikel fasst die wichtigsten Merkmale der Spinnentiere zusammen. Der Körper der Spinnentiere besteht aus zwei Teilen, dem Prosoma und dem Opisthosoma. Sie haben vier Paar Laufbeine und keine Facettenaugen wie die Insekten. Bei der Fortpflanzung gibt es verschiedene Variationen, aber die meisten Arten haben eine innere Befruchtung oder legen Spermienpakete ab. Die Spinnentiere werden in verschiedene Ordnungen unterteilt, darunter Milben, Webspinnen, Weberknechte, Skorpione und andere. Es werden auch einige Literaturquellen und Webseiten über Spinnentiere erwähnt.