Arachnids
Author: Ray Bowers

Description:
All of the orders in chelicerates were present in the Carboniferous period, from 360 to 245 million years before present. This ancient group has two distinct body regions: the prosoma, head and thorax areas, and the abdomen. These two body segments are fused in mites. The paired appendages consist of chelicerae, jaw-like structures that are used in feeding, pedipalps, that have a variety of shapes and functions, and four pairs of legs.

Gas exchange is by book lungs or trachea, air tubes. Digestion is started externally as digestive enzymes are mixed as the tissue is torn by the chelicerae. The rest of the digestion takes place in the tubular digestive tract.

Geographic Range:
Arachnids are found on every continentant. Some have a broad range and others are quite restricted.

Habitat:
All terrestrial environments have been occupied. A few groups are also aquatic.

Food Web:
Most arachnids are carnivores, and some have specialized to become external parasites.

Reproduction and Development:
Fertilized eggs may be left in suitable area in the environment or they may develop within the female. Sometimes the eggs are deposited in a silk sack that is guarded by the female. When the eggs hatch, the young may be on their own or they may ride on their mother's back until they disperse. In some groups the young disperse after the first molt, but in others several molts occur before dispersal.

Behavior:
Most arachnids are active hunters, and some use venom to help subdue their prey. Since most arachnids are predators, most have evolved unique behaviors to keep the male from becoming a meal for the female, these behaviors do not always work.

Ecosystem Roles:
The arachnids play an important role in limiting the size of other arthropod populations, especially insects.

Conservation:
Some arachnids are pests, such as ticks and mites, but most are beneficial and should be protected.

Taxonomy:

Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida, Arachnids

The following eleven orders occur in New Mexico:

Scorpiones: Scorpions, such as Vaejovis vittatus
Pseudoscopiones: False Scorpions
Solifugae: Wind Scorpions, Mata Venado, or Sun Scorpions
Palpigradi: Microwhip Scorpions
Uropygi: Whip Scorpions
Amblypygi: Amblypygids
Araneae: Spiders, such as tarantulas
Ricinulei: Ricinuleids
Opiliones: Harvestmen or Daddy-longlegs
Acarina: Mites and Ticks

References:
Borror, Donald J. and Richard E. White. 1970. A Field Guide to the Insects of America North of Mexico. Boston: Houghton Mifflin Co.

Barnes, Robert D. 1980. Invertebrate Zoology. Philadelphia: W. B. Saunders Co.

Borror, Donald J., Charles A. Triplehorn, and Norman F. Johnson. 1989. An Introduction to the Study of Insects. Philadelphia:W. B. Saunders Co.

Levi, Herbert W. and Lorna R. Levi. 1987. Spiders and Their Kin. Racine, Wisconsin: Golden Press.

Related Terms: Arachnida, Chelicerates