2007 Volume 22 Pages 20-30
The spider genera Cybaeus (Cybaeidae) and Arcuphantes (Linyphiidae) comprise numerous species endemic to Japan. They are considered to have diverged as the result of geographic isolations, probably enhanced by their low dispersal abilities. The current paper analyses the species composition and geographic differentiation in the genera Cybaeus and Arcuphantes in western Honshu and adjacent areas. The genus Cybaeus contains species with a wide range body lengths (from ca. 3 to 15mm), with local species assemblages usually consisting of representatives of different size classes. Local species assemblages often constitute a group of closely related species, together with other similar-sized species that are allopatrically or parapatrically distributed with one another. Diversity in genital morphology and geographic differentiation patterns are discussed for species-groups of Cybaeus (C. nipponicus, C. kuramotoi-group, C. miyosii-group and C. hiroshimaensis-group) in western Japan. The kuramotoi-group, which contains species of medium size (approximately 5 to 7mm in body length), has the most diverse genital morphology and is characterized by the presence of a mating plug. The Arcuphantes longiscapus-group is composed of closely related but distinct species based on their morphology and geographical distribution. The group contains eight species that are distributed in western Honshu, northeastern Shikoku and some adjacent islands, Japan, but the distribution patterns are parapatric except for a few cases of narrow overlap. Among these species, morphology of the male palp and female epigynum was strictly speciesspecific. They operate like a lock-and-key system, so that mating is only possible between individuals of the same species.
Circular of the Japanese Society of Systematic Zoology
