Spiders (Araneae) can be placed within a series of nested clades within Arachnida. Arachnopulmonata encompasses all arachnids with book lungs. Pantetrapulmonata encompasses arachnids with four pairs of lungs in their ground pattern. Tetrapulmonata potentially encompasses pantetrapulmonate arachnids which have reduced the number of lateral eye lenses and endites on the coxae of the first pair of walking legs. Serikodiastida encompasses arachnids with opisthosomal silk glands. Several spider-like fossils, some of which were previously interpreted as spiders, may belong either here or in the wider tetrapulmonate group. Araneida encompasses arachnids with spinnerets and a male palpal organ, and fossils reveal that the common ancestor of spiders would have retained a flagelliform telson. Araneae can thus be defined as spiders which have lost the telson, something which appears to have occurred multiple times among arachnids. The oldest fossil example of each of these clades is documented, and compared to molecular estimates of origination dates where available, to yield a broad temporal and phylogenetic framework for spider origins.
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Vol. 19 • No. sp1