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Arachnids are arthropods in the class Arachnida (/ ə ˈ r æ k n ɪ d ə /) of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons. [2] Adult arachnids have eight legs attached to the cephalothorax.
Diagram of a spider leg and pedipalp – the pedipalp has one fewer segment. Arachnid legs differ from those of insects by the addition of two segments on either side of the tibia, the patella between the femur and the tibia, and the metatarsus (sometimes called basitarsus) between the tibia and the tarsus (sometimes called telotarsus), making a total of seven segments.
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 ventral side of a brown widow spider . The epigastric plates and furrow are visible, as well as the hourglass marking on the underside of the abdomen, which is a characteristic feature of widow ...
The Opiliones (formerly Phalangida) are an order of arachnids, colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs (see § Etymology below). As of July 2024, over 6,650 species of harvestmen have been discovered worldwide, [1] [2] [3] although the total number of extant species may exceed 10,000. [4]
The word arthropod comes from the Greek ἄρθρον árthron ' joint ', and πούς pous (gen. ποδός podos) ' foot ' or ' leg ', which together mean "jointed leg", [4] with the word "arthropodes" initially used in anatomical descriptions by Barthélemy Charles Joseph Dumortier published in 1832. [1]
Pedipalps (commonly shortened to palps or palpi) are the secondary pair of forward appendages among chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and anterior to the first pair of walking legs.
An intriguing arthropod ancestor. The 3D scans revealed two nearly complete specimens of Arthropleura that lived 300 million years ago. Both fossilized animals still had most of their legs, and ...
Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids. [5]Trigonotarbids share many superficial characteristics with spiders, including a terrestrial lifestyle, respiration through book lungs, and walking on eight legs, [6] with a pair of leg-like pedipalps near the mouth and mouth parts.