Class Arachnida (Arachnids)
- Possess chelicera.
- Powerful sucking stomach or muscular pharynx.
- Possess a number of sense organs.
- Internal fertilization.
- Absence of compound eye.
- Production of silk.
- Successful predators.
- Possess poison glands.
- 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:
- 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
- Arachnids kill their prey by crushing or injecting them with a venon.
Some Pertinent Books Found in Lamson Library:
- Barnes, R.S.K., Calow, P., and Olive, P.J.W. 1988. The
Invertebrates: a new synthesis. Oxford: Blackwell
- Snow. 1970. The Arachnids: An Introduction. New York:
(Rebecca Langlais, Fall 1994; edited by T. Shultz, Spring 1995)