Acarina
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Acarina or Acari is an order of arachnids that consists of mites and ticks. Though acarina are small to minute, they are extremely numerous. More than 30,000 species have been described (as of 2005), and it is estimated that there are half a million more still undescribed.
Morphology
The body is oval and the two segments (prosoma (cephalothorax) and opisthosoma (abdomen)) are usually undifferentiated. Most adults have four pairs of legs, like other arachnids. However, the larvae hatch with only three pairs of legs; the fourth one is only acquired at the first molt. Some acarina have less than three pairs of legs, like the gall mite Phyllocoptes variabilis (Family Eriophyid), which is wormlike and only has two pairs of legs. The immature instars between the first molt and adulthood are called nymphs.Diversity and lifestyles
Acarina are extremely diverse. They live in practically every habitat, and include aquatic (freshwater and sea water) and terrestrial species. They outnumber other arthropods in the soil organic matter and detritus. Many are parasitic, and they affect both vertebrates and invertebrates. Most parasitic forms are external parasites, while the free living forms are generally predaceous and may even be used to control undesirable arthropods. Others are detritivores that help to break down forest litter or dead skin debris. Others still are plant feeders and may damage crops.Economic importance
The damage made to crops is one economic effect of acari, but this is not the most important. Some parasitic forms affect humans and other mammals, causing damage by their feeding, and can even be vectors of disease. A well known effect of acarina on humans is their role as an allergen and the stimulation of asthma in people affected by the repiratory disease. Their potential utility for pest control is also of importance.Suborders
The phylogeny of the order is still disputed.
- Acariformes is a suborder consisting mostly of mites.
- Superfamilies:
- *Trombidiformes
- *Sarcoptiformes
- **Endeostigmata
- **Oribatida
- **Astigmata
- Parasitiformes is a suborder consisting mostly of ticks.
- Superfamilies:
- *Mesostigmata
- *Ixodida (ticks)
- *Holothyrida
- Opilioacariformes is a small suborder of atypic acarina that are elongate and leathery with a segmented abdomen and bright colours. They are omnivorous or predatory and superficially similar to harvestmen (opiliones, hence their name).
- There are also a number of unassigned genera.
References
- [Acari]
- *[Acariformes]
- *[Parasitiformes]
- [Key to Families and Subfamilies of Water Mites (Hydracarina) in Australia]
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