Two species groups of the social spider genusAnelosimusare revised. Theethicusgroup contains six species found in South America, in an area ranging from the Guianas to southern Brazil and Argentina. Of these,A. rabusLevi, 1963,A. ethicus( Keyserling, 1884 ), andA. nigrescens( Keyserling, 1884 ) are redescribed, whileA. nigrescensis removed from synonymy withA. ethicus. Three new species are described:A. misionessp. nov.,A. sumisolenasp. nov. andA. inhandavasp. nov.Anelosimus ethicusis reportedly either subsocial or solitary, while the behaviour of the other species in the group is unknown. Therupununigroup contains two quasisocial species,A. rupununiLevi, 1956 andA. lorenzoFowler & Levi, 1979, from the Caribbean and tropical South America. Both are redescribed here. A parsimony analysis of morphological characters provides support for the monophyly of both groups. In the phylogeny, subsociality optimizes to the base ofAnelosimus, indicating that the common ancestor of theethicusgroup was subsocial. Its members can thus be predicted to be subsocial, or secondarily solitary. Quasisociality arosede novoin therupununigroup, representing one of 6−7 independent origins in theridiids. Study of the biology ofAnelosimusis important to advance our understanding of the evolution of sociality in spiders.
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Ingi Agnarsson (2005) studied this question.
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