Cribellate spiders

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Cribellate spiders (Cribellatae) are real weaving spiders that, thanks to special organs, are able to produce catching wool for their spider webs without any glue droplets . They are fundamentally different from the ecribellate spiders that produce threads of glue. Cribellatae and Ecribellatae were previously treated as infraorders because of their amazing differences in the production of their spider silk. Today one follows instead the division into Haplogynae and Entelegynae , which is based on the structure of the sexual organs and includes both cribellate and ecribellate spiders.

The cribellate traps

The composite catch threads of the cribellate spiders consist of one or two axis threads, strong crimped edge threads and the even finer and very dense catch wool, which is very effective even without glue and consists of single threads with a diameter of less than 15 nm. With the calamistrum on the last pair of legs, the cribellate spiders brush this trapping wool in bundles onto the axis threads. The resulting composite catch cords usually have a bluish shimmer and look like tails in which the prey are helplessly entangled. The adhesion here is not based on glue droplets, as is the case with the ecribellate spiders.

One advantage of the glue-free cribellate threads is that they do not dry out like glue threads and have to be replaced. This enables many species, such as members of the cribellate families Psechridae and the curling- wheel web spiders, to continuously build their webs of impressive size. Others form aggregations and colonies with permanent nets, such as Philoponella arizonicus and Philoponella oweni in Central America.

The cribellate spiders do without the production of this fishing wool for the production of the framework of their web. The basic construction of the trap is made solely with the stronger axle threads.

Cribellum and Calamistrum

The cribellum is very likely a homology of the anterior, middle spinnerets of the articulated spiders (mesothelae) and the four pairs of active spinnerets of the hypothetical archetype of the spider . In the case of the ecribellate spiders, there is a probably functionless hill at this point, the Colulus. The cribellum, also called spinning plate, is a plate that is densely packed with up to 40,000 or 50,000 spinning bobbins. The number of bobbins increases with each moult. These spinning bobbins are small tubes or openings from which 10–15 nm thin, knotty structured threads are excreted. As with other spiders, the silk is produced here using common spinnerets .

The calamistrum is similar to a comb that sits on the metatarsus (last leg link) of the fourth pair of legs. Each bristle of this bristle comb is covered with a row of teeth. In some species the calamistrum of the males is only indistinctly pronounced. The fishing wool is combed from the cribellum with the calamistrum and applied to the thicker axis threads.

The Cribellaten problem

Since it is unlikely that such distinctive forms as cribellum and calamistrum have arisen several times independently of one another, it is assumed that all cribellate spiders have a common ancestor. Since the cribellum is reduced to the colulus in the Ecribellates or is completely absent (like the calamistrum), it was natural to conclude that they developed from the cribellates, i.e. that the two groups are each monophyletic . Therefore, it has long been customary in the systematics of the real spiders to treat Cribellatae and Ecribellatae as infraorders .

Today it seems more likely that cribellum and calamistrum are part of the basic blueprint of modern spiders; That is, the last common ancestor of all recent spiders with the exception of the limb spiders had these structures. In the course of evolution, the ecribellate "glue web" has been developed from this convergent many times. Many families even lost both types of networks; that is, they have switched to the free-hunting way of life as a secondary feature. This view is also supported by molecular family trees (based on homologous DNA segments). This also gave new insights into the evolution of the cycle network. While it was previously assumed that this was developed independently of each other in cribellate and ecribellate spiders (i.e. convergent ), it now seems more probable that all spiders that build wheel webs, whether with cribellate or glue threads, are more closely related to one another, so that the web represents a homology .

Cribellate families

source

  • Rainer F. Foelix: Biology of the spiders . Georg Thieme Verlag, Stuttgart 1979, ISBN 3-13-575801-X
  1. ↑ Jeremy A. Miller, Anthea Carmichael, Martín J. Ramírez, Joseph C. Spagna, Charles R. Haddad, Milan Rezác, Jes Johannesen, Jirí Král, Xin-Ping Wang, Charles E. Griswold (2010): Phylogeny of entelegyne spiders : Affinities of the family Penestomidae (NEW RANK), generic phylogeny of Eresidae, and asymmetric rates of change in spinning organ evolution (Araneae, Araneoidea, Entelegynae). Molecular Phylogenetics and Evolution 55: 786-804. doi: 10.1016 / j.ympev.2010.02.021
  2. ↑ Joseph C. Spagna & Rosemary G. Gillespie (2008): More data, fewer shifts: Molecular insights into the evolution of the spinning apparatus in non-orb-weaving spiders. Molecular Phylogenetics and Evolution Volume 46, Issue 1: 347-368. doi: 10.1016 / j.ympev.2007.08.008
  3. ↑ Todd A. Blackledge, Nikolaj Scharff, Jonathan A. Coddington, Tamas Szuts, John W. Wenzel, Cheryl Y. Hayashi, Ingi Agnarsson (2009): Reconstructing web evolution and spider diversification in the molecular era. Proceedings of the National Academy of Science USA vol. 106 no.13: 5229-5234. doi: 10.1073 / pnas.0901377106
  4. ↑ a b Gertsch, Willis J .: American Spiders, 2nd edition. Van Nostrand Reinhold, New York 1979, ISBN 0-442-22649-7

Further literature

  • S. Baum (1974): On the "Cribellaten problem": The genital structures of the Oecobiinae and Urocteinae (Arach .: Aran .: Oecobiidae). Abh Verh Naturwiss Ver Hamburg 16: 101–153
  • P. Lehtinen (1967): Classification of the cribellate spiders and some allied families, with notes on the evolution of the suborder Araneomorpha. Ann Zool Fenn 4: 199-468