The tracheal arrangement and the classification of linyphiid spiders

The tracheal arrangement of 121 species of European Linyphiidae has been examined. Tracheal systems support the division of the family into two major groups: Linyphiinae have four simple tracheae arising from the spiracular atrium which are confined to the abdomen, whilst Erigoninae have large medial trunks which divide into numerous small branches before passing as two bundles through the pedicel to the prosoma, and short, simple lateral tracheae. In the majority of Erigoninae the medial branches are without taenidia and can be regarded as tracheoles but in Hilaira, Donacochara, Leptorhoptrum and Drepanotylus the branches possess taenidia. Allomengea is anomalous in that the medial tracheae are extensively branched but remain confined to the abdomen. Carorita, Mioxena, Wiehlea, Lessertiella, Jacksonella, Asthenargus, Aphileta and Ostearius, which have been regarded as Erigoninae on the grounds of genital anatomy, all possess linyphiine tracheal systems. The significance of these findings is discussed.