Arachnid
Arachnid (əˈraknɪd)
Arachnids are a class of joint-legged invertebrate animals, in the subphylum Chelicerata. Arachnids include spiders, scorpions, ticks, and mites. They are characterized by the possession of a two-segmented body and four pairs of legs.
Etymology
The term "Arachnid" comes from the Greek ἀράχνη (aráchnē), meaning "spider".
Characteristics
Arachnids are mostly carnivorous, feeding on the pre-digested bodies of insects and other small animals. Many are venomous - they secrete poison from a specialized gland to kill prey or enemies. Others are parasites, some of which are carriers of disease.
Arachnids have two main body parts: the cephalothorax (fused head and thorax) and the abdomen. The cephalothorax is covered by a carapace, has six pairs of appendages, the first of which are the chelicerae, the next are the pedipalps and the last four pairs are the walking legs.
Classification
Arachnids belong to the phylum Arthropoda, which also includes insects, crustaceans, and myriapods. They are further classified into eleven orders - Araneae (spiders), Scorpiones (scorpions), Opiliones (harvestmen), Acari (ticks and mites), Amblypygi (whip spiders), Palpigradi (microwhip scorpions), Pseudoscorpiones (pseudoscorpions), Schizomida (shorttailed whipscorpions), Solifugae (camel spiders), Thelyphonida (whip scorpions), and Ricinulei (hooded tickspiders).
Related Terms
- Chelicerae: The mouthparts of the Chelicerata.
- Pedipalps: The second pair of appendages of the Chelicerata.
- Arthropoda: A phylum of animals that have a segmented body and jointed appendages.
- Araneae: An order of arachnids, which includes spiders.
- Scorpiones: An order of arachnids, which includes scorpions.
- Acari: An order of arachnids, which includes ticks and mites.
External links
- Medical encyclopedia article on Arachnid
- Wikipedia's article - Arachnid
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