The subphylum Chelicerata comprises two classes; the Merostomata and the Arachnida. Whereas merostomes are aquatic, the arachnids are confined to the terrestrial realm, except for a few forms which are secondarily adapted to living in water.
The Arachnida encompass all spiders, scorpions, pseudoscorpions, mites, ticks, harvestmen and opiliones.
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Last updated: 20.11.05
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