Class Arachnida

Major Attributes:
  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.

Some Interesting Facts:

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.

(Rebecca Langlais, Fall 1994; edited by T. Shultz, Spring 1995)