Spiders are ecologically important predators with complex
venom and extraordinarily tough silk that enables capture of large prey. Here
we present the assembled genome of the social velvet spider and a draft assembly
of the tarantula genome that represent two major taxonomic groups of spiders.
The spider genomes are large with short exons and long introns, reminiscent of
mammalian genomes. Phylogenetic analyses place spiders and ticks as sister
groups supporting polyphyly of the Acari. Complex sets of venom and silk
genes/proteins are identified. We find that venom genes evolved by sequential
duplication, and that the toxic effect of venom is most likely activated by
proteases present in the venom.