PhD Arthur Decae 2010 - Ghent Ecology - Universiteit Gent

most seen and studied groups, but actually they represent the exception rather than the rule. It
is insufficiently realized by students of spiders (arachnologists) that the most conspicuous
spiders naturally draw most of the attention and that much hypothesizing and theorizing in
Arachnology is biased to explaining the ways of these ‘aberrant’ spiders. Most spider species,
as virtually all their arachnid relatives, are nocturnal and secretive creatures that live in hidden
and sheltered positions and that, because of this, have attracted little attention from zoologists.
Following conventional taxonomical wisdom the Order Araneae (spiders) contains two
Suborders: Mesothelae and Opisthothelae. The Mesothelae contain only one family of living
spiders: Liphistiidae. The Opisthothelae are further subdivided into two Infraorders (see frontpage
illustration): Mygalomorphae and Araneomorphae (Platnick & Gertsch 1976). Only the
Mygalomorphae are of further concern here.
Mygalomorphae
Mygalomorph spiders are a prime example of a group of understudied secretive living
arachnids. Nevertheless, the mygalomorph spiders are a major group of animals in themselves
(320 genera, 2643 species known). They occur in most terrestrial and some semi-aquatic
environments on all continents except Antarctica. In many habitats they are among the
dominant predators of ground living arthropods and some species at least incidentally prey on
other animal groups including small vertebrates (Raven 2010). Mygalomorphae are primitive
spiders that have retained many ancestral traits including their way of living. Just as in the
true spiders of the Infraorder Araneomorphae however, some successful diversification has
taken place within the Mygalomorphae. The large bird-spiders of the family Theraphosidae
are a fine example. Some species in this family that have adopted a more actively hunting and
wandering way of life, have been very successful. Their biological success is reflected in the
highest known species diversity among mygalomorph spiders and an almost worldwide
distribution in the warmer climate zones.
Table1. List of Arachnida taxa, with their first appearance in the fossil record and their status of being,
living or extinct (after Dunlop & Selden 2009). Note the Paleozoic origin of all taxa except
Schizomida and Palpigradi. Fossil traces of these two taxa of small and fragile bodied animals have
not as yet turned up in Paleozoic rocks.
TAXON OLDEST RECORD GEOLOGICAL PERIOD STATUS
myBP
1 Scorpiones 428 Silurian Living
2 Trichonotarbida 419 Silurian Extinct
3 Phalangiotarbida 411 Devonian Extinct
4 Opiliones 410 Devonian Living
5 Acari 410 Devonian Living
6 Pseudoscorpiones 392 Devonian Living
7 Uraraneida 392 Devonian Extinct
8 Ricinulei 319 Carboniferous Living
9 Thelyphonida 319 Carboniferous Living
10 Haptopoda 312 Carboniferous Extinct
11 Araneae 312 Carboniferous Living
12 Amblypygi 312 Carboniferous Living
13 Solifigae 308 Carboniferous Living
14 Schizomida 34 Oligocene Living
15 Palpigradi 5 Pliocene Living