Taxonomy

Tarantulas belong to the family Theraphosidae. The family Theraphosidae includes over 800 different species of tarantulas, divided over 12 subfamilies. Tarantulas (Theraphosidae) are primitive spiders. The jaws (chelicerae) move in a inward motion instead of a scissoring motion and lack fine breathing tubes (tracheae) of true spiders.

Arachnids are animals that have an exoskeleton; lack an internal bone structure instead they have a stiff outer layer which acts as a hard shell. The exoskeleton is made up of layers of carbohydrates and protein, named chitin. It provides protection but no growth. Instead of growing, arachnids molt. A new exoskeleton pushes through with a thin layer of fluid separating the old from the new. Arachnids have 8 jointed legs while insects have six and they do not have a backbone. The body is divided into a two-part segmented body; the prosoma and the abdomen. The prosoma anchors the chelicerae (pincers), pedipalps (mouth parts) and four pairs of legs. They are cold-blooded; their body temperature depends on the temperature of their environment. Arachnids breathe air through book-lungs, gill-like structures. One of the largest differences between tarantulas and true spiders are the fangs. The arrangement of tarantulas fangs facilitate very little movement allowing to strike in a stabbing motion with limited capacity. True spiders have fangs capable of a much broader range of movement giving them the ability to strike prey in various angles.

Other taxomical differences; tarantulas are limited to only two pairs of spinnerets compared to true spiders three and tarantulas have two pairs of booklungs rather than one pair true spiders have. Differences like this illustrate how very little has changed from the ancient descendent tarantula to the modern day tarantula.

Classification

Kingdom: Animalia

Phylum: Arthropoda

Class: Arachnida

Order: Araneae

Suborder: Mygalomorphae

Superfamily: Theraphosoidea

Family: Theraphosidae

Subfamilies: Acanthopelminae, Aviculariinae, Eumenophorinae, Harpactirinae, Ischnocolinae, Ornithoctoninae, Poecilotheriinae, Selenocosmiinae, Selenogyrinae, Stromatopelminae, Theraphosinae and Thrigmopoeinae

Due to the complex taxonomy no one can 100% identify a tarantulas by written descriptions or image. At the best all you can get is a hypothesis; educated guess. To get a positive identification you have to send out a carcass to a lab and even then they may ask for samples from both sexes. You have to keep in mind many species have different appearances at developmental stages, sexes and climates. Due to this even the scientific community has labeled species incorrectly to only find that two differently labeled species are the same but opposing sexes.

Sources:

Spiders, HarperCollins Publishers, Paul Hillyard, 2006

Arachnida, Wikipedia, August 27, 2006: http://en.wikipedia.org/wiki/Arachnida

Tarantula, Wikipedia, August 25, 2006: http://en.wikipedia.org/wiki/Theraphosidae

Theraphosidae, Wikispecies, Tamerlan Thorell, 1870: http://species.wikimedia.org/wiki/Theraphosidae

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