Taxonomy and Phylogeny of Spiders
More than 47.000 species are listed in the World Spider Catalog (2018). These are classified into 116 families. Every day new species are described and estimates reach 120.000 spider species on Earth.
Systematics of spiders (major clades) is relatively stable, but monophyly of several classic groups as well as the position of families (and genera) in the Tree of Life are still changing according to new data and analyses and discussed steadily.
Recent analyses of a transcriptome-based data set comprising 70 ingroup spider taxa led to a much better resolution of spider evolutionary relationships (Garrison et al. 2016). Previous incongruences between the traditional spider classification scheme and (non-phylogenomic) molecular systematics appear to be caused by just too few data. Non-molecular datasets to date have been restricted to a relatively small set of morphological and/or behavioral characters whereas molecular analyses addressing deep spider relationships have largely employed relatively few, rapidly evolving loci (Garrison et al. 2016).
The new phylogenomic analyses corroborate several well-accepted high level groupings: Opisthothele, Mygalomorphae, Atypoidina, Avicularoidea, Theraphosoidina, Araneomorphae, Entelegynae, Araneoidea, the RTA clade, Dionycha and the Lycosoidea. On the other hand, they question the monophyly of Eresoidea, Orbiculariae, and Deinopoidea. The composition of the major paleocribellate and neocribellate clades, the basal divisions of Araneomorphae, appear to be falsified and traditional Haplogynae is in need of revision. Many families were still not included and several positions remain uncertain.
Some important new perceptions
Palaeocribellatae include only one recent family (Hypochilidae) and Neocribellatae all other Araneomorphae (with venom glands reaching into the prosoma).
The orb web originated earlier than previously supposed, but got lost at least three times independently.
Contrary to the contemporary paradigm that the evolution of the orb web and adhesive
sticky threads elevated rates of diversification among the araneoid spiders, the new analysis indicates that the highest rates of diversification likely occurred among the RTA spiders followed by mygalomorphs and then araneoids as a distant third, the latter driven–in part–by the secondarily non-orb weaving theridiids and linyphiids.
This interestingly implies that other foraging strategies like cursorial hunting and irregular sheets were a more ‘‘successful’’ strategy than the orb, probably related to the enormous diversification of insects (among them litter inhabiting ants and beetles) during the Cretaceous Terrestrial Revolution.
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