Functional organization of the spinning apparatus of Cyrtophora citricola with regard to the evolution of the web (Araneae,Araneidae)

Summary The spinning apparatus of Cyrtophora citricola closely corresponds to that of orb-weaving Araneidae, two peculiarities excepted. Firstly the spigots of the piriform glands differ extremely in size, the smallest of them being numerous and having a unique location on the anterior spinnerets. Secondly, the triad complex (on the posterior spinnerets) used by other Araneidae for producing gluey capture threads is lacking. Both these characteristics are correlated with the construction of a fine meshed sheet of dry silk by Cyrtophora instead of orbwebs with capture spirals. The sheet can be understood as being a very much enlarged central area of orb-webs. Since vestiges of triads could be found in early developmental stages of C. citricola, the origin of the meshed sheet from orb-webs with gluey capture threads is clearly demonstrated. The paper includes a study on how the spider produces thread attachments by means of the secretions of the piriform glands.