Class Arachnida

1. Possess chelicera.
2. Powerful sucking stomach or muscular pharynx.
3. Possess a number of sense organs.
4. Internal fertilization.
5. Absence of compound eye.
6. Production of silk.
7. Successful predators.
8. Possess poison glands.
9. Body divided into two parts: prosoma and opisthosoma.

The land-based arachnids comprise over 98% of living chelicerate species and display a number of marked adaptions to terrestrial existence. The arachnids consist of 6 major groups: ticks and mites, scorpions, spiders, harvestmen, pseudoscorpions, and sun spiders. They have a malpighian-tubule excretory system and also have internal air-breathing gaseous exchange organs. They have a cuticle that is waterproofed by a wax layer.

• Arachnids range in size 0.1mm to 18cm and include over 62,000 species. The scorpions are the largest of the arachnids and measure 5-8 inches in length. Mites usually measure less than 1mm in length.
• They are fliud-feeders and obtain their food from living or dead animals or plants.
• Ticks are regarded as one of the most serious pests known to humans and domestic animals. They can cause physical damage, and may produce severe illness or even death.
• Spiders are mostly harmless to humans. Their prey is captured either by being grasped and physically overcome by being trapped in a silken web.
• Arachnids kill their prey by crushing or injecting them with a venon.

Some Pertinent Books Found in Lamson Library:

1. Barnes, R.S.K., Calow, P., and Olive, P.J.W. 1988. The Invertebrates: a new synthesis. Oxford: Blackwell Scientific Publications.
2. Snow. 1970. The Arachnids: An Introduction. New York: Columbia University.