Abstract
The desmitracheate system in a “micronetine” genus Nippononeta Eskov, 1992 is recognized for the first time in the present study. This makes the subfamilial placement of this genus problematic. A morphological study was conducted for Nippononeta kurilensis Eskov, 1992 (the type species of Nippononeta) and Nippononeta coreana (Paik, 1991). Characters of genitalia and tracheal system, as well as some somatic characters were studied in detail by using scanning electronic microscopy (SEM), and compared with those of Agyneta. Updated descriptions of the genus Nippononeta and its two species are presented. Putative synapomorphies for Nippononeta and Agyneta are provided, as well as some putative synapomorphies shared by the two genera. The results imply that both scaped epigynum and desmitracheate tracheal system are probably homoplastic. The placement of Nippononeta and Agyneta within Linyphiidae need to be resolved in future studies.
Highlights
Linyphiidae Blackwall, 1859 is the second largest spider family, including over 4,500 species (World Spider Catalog 2014)
Analyzing more groups that possess transitional characters between the typical “micronetine” and erigonine versions may help us infer the character evolution and resolve the phylogenetic relationships among linyphiid groups. We report another “micronetine” genus Nippononeta Eskov, 1992, having a scaped epigynum, and a desmitracheate system
The putative synapomorphies based on genital characters suggest that the four desmitracheate “micronetine” genera: Nippononeta, Agyneta, Tennesseellum, and Anibontes have a common ancestor
Summary
Linyphiidae Blackwall, 1859 is the second largest spider family, including over 4,500 species (World Spider Catalog 2014). The epigynum furnished with a scape carrying copulatory grooves and openings (referred to as “scaped epigynum” below) was used as the main diagnostic feature for Micronetinae Hull, 1920 (Millidge 1984; Saaristo and Tanasevitch 1996), and the desmitracheate tracheal system, in which the median trunks are extensively branched and extend into the prosoma, was used as the main diagnostic feature for Erigoninae (Blest 1976; Millidge 1984) Both scaped epigynum and desmitracheate system can be found in the “micronetine” genera: Tennesseellum Petrunkevitch, 1925, Agyneta Hull, 1911 (including Meioneta Hull, 1920, a junior synonym of Agyneta), and Anibontes Chamberlin 1924 (Millidge 1986; Hormiga 1994; Dupérré 2013). Putative synapomorphies were proposed for Nippononeta and Agyneta, which need to be tested in future studies
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