Evolution of spiders

Common card · No. 382886

Spiders have existed for at least 380 million years. The group's origins lie within an arachnid sub-group defined by the presence of book lungs (the tetrapulmonates); the arachnids as a whole evolved from aquatic chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. There may be more than 120,000 species. Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. Both extant and fossil species are described annually by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion.

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