Mygalomorphae
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Mecicobothriidae |
The Mygalomorphae, (also called the Orthognatha), are an infraorder of spiders. The latter name comes from the orientation of the fangs which point straight down and do not cross each other (cf araneomorph).
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[edit] Description
This suborder includes the heavy bodied, stout legged spiders popularly known as tarantulas as well as the dangerous Australasian funnel-web spiders.
Like the "primitive" Mesothelae, they have two pairs of book lungs, and downward pointing chelicerae. Because of this, the two groups were once believed to be closely related. Later it was realized that the common ancestors of all spiders had these features (Symplesiomorphy), and that the mygalomorphs just retained them, while the closely related araneomorphs evolved new features (including a cribellum). [1]
Almost all species have eight eyes, however there are some with less (Masteria lewisi has only six eyes).
They have ample poison glands that lie entirely within their chelicerae, but only spiders of the Australian genus Atrax can be really harmful to humans. Their chelicerae and fangs are large and powerful. Occasionally members of this suborder will even kill small fish, small mammals, etc.
While the world's biggest spiders are mygalomorphs (Theraphosa blondi (LATREILLE, 1804) has a body length of 10cm, and a leg span of 28cm), some species are less than one millimeter long. Mygalomorphs are capable of spinning at least slightly adhesive silk, and some build elaborate capture webs that approach a meter in diameter.[1]
Unlike Araneomorphae, which die after about a year, Mygalomorphae can live for up to 25 years, and some don't reach maturity until they are about six years old.[2]
[edit] Distribution
Most members of this infraorder occur in the tropics and subtropics, but their range can extend farther north, e.g. into the southern and western regions of the United States.
Only few species occur in Europe. These are of the orders Atypidae, Nemesiidae, Ctenizidae, Hexathelidae, Theraphosidae and Cyrtaucheniidae, together with only a dozen species.
[edit] Systematics
The Mygalomorphae are divided into two infraorders, the Tuberculotae and Fornicephalae.
Mecicobothrioidea:
+--Mecicobothriidae (8 species)
+--------------------------|
| +--Microstigmatidae (13 species)
+--Tuberculotae-|
| | +-------------------------Hexathelidae (86 species)
| +---| +-----------------------Dipluridae (175 species)
| +-| +---------------------Nemesiidae (ca. 340 species)
| +-| +-------------------Barychelidae (ca. 300 species)
| +-| +--Paratropididae (8 species)
-| +-Theraphosoidea-|
| +--Theraphosidae (ca. 900 species)
|
| +--Atypidae (40 species)
| +----------------Atypoidea-|
| | +--Antrodiaetidae (32 species)
+-Fornicephalae-|
| +-------------------------Cyrtaucheniidae (126 species)
+---| +---------------------Idiopidae (ca. 270 species)
+---| +------------------Ctenizidae (120 species)
+--| +--Actinopodidae (41 species)
+------Migoidea-|
+--Migidae (91 species)
- Cladistic hypothesis for Mygalomorphae, after [3]. Line length does not relate to evolutionary distance.
[edit] References
- ^ a b Coddington, J.A. & Levi, H.W. (1991). Systematics and Evolution of Spiders (Araneae). Annu. Rev. Ecol. Syst. 22:565-592
- ^ About Spiders
- ^ Raven, Robert, J. (1985). The spider infraorder Mygalomorphae: Cladistics and systematics. Bull. Am. Mus. Nat. Hist. 182:1-180
- Goloboff, P.A. (1993). A Reanalysis of Mygalomorphae Spider Families (Araenae). American Museum Novitates 3056. PDF
