Chelicere

Hypostome and chelicerae in the common wood tick ( Ixodes ricinus )

The characteristic feature of the jaw-claw bearer (Chelicerata) is called Chelicere (common language Chelizere ) or jaw claw . This is an extremity in the head area that has been converted into a mouth tool and is located in front of the mouth opening.

Structure and system

The chelicere is primarily tripartite and provided with scissors (chela). During embryonic development , the chelicerae are placed behind the mouth opening and then later move forward.

According to the traditional view, the chelicerae are supplied with nerves by the third part of the brain (tritocerebrum) and would be correspondingly homologous with the second antennae of the crabs. Recent studies suggest a three-part (tripartite) brain for the Chelicerata as well. Accordingly, the chelicerae are more likely to be innervated by the deutocerebrum. Accordingly, they would be homologous to the first antennae of crabs and the antennae of insects.

Within the Chelicerata, the Chelicere and the following extremity ( pedipalp in arachnids ) are modified in many ways. The three-part scissors are still found in woodlice spiders , horseshoe crabs , scorpions , palpebras and mites .

In the summarized as Megoperculata scourge scorpions , amblypygi and spiders the Chelicere consists of only two members, said second member against the first is einschlagbar (Pseudo chelators). In spiders it is also provided with a large poison gland that can reach far into the spider's front body ( prosoma ). In the original weaving spiders, such as the tarantula-like , the chelicerae are directed forward, the claws are folded down parallel to each other. This condition is known as orthognath . In more highly developed spiders ( real spiders , Araneomorphae) the chelicerae are placed vertically and at the same time turned inwards. In this way they can be opened like pliers at the base and work against each other. It is the labidognathic state.

The pseudoscorpions and roller spiders combined as Haplocnemata as well as the hooded spiders have a two-part chelicere, which, however, forms a real pair of scissors here. In the case of the pseudoscorpions, the chelicere is also equipped with the exits of the spinneret glands and cleaning combs (Serrulae: Serrula exterior and Serrula interior).

Forward-facing chelicerae (orthognath) of a red chile tarantula ( Grammostola rosea ).
Inwardly directed chelicerae (labidognathen) of the wet nurse's thorn finger ( Cheiracanthium punctorium ), a real spider . Poison leaks from the ends of the claws.

supporting documents

↑ Chelizere. In: Duden online . Retrieved June 25, 2019 .
↑ ^a ^b ^c ^d ^e ^f Peter Weygoldt: Chelicerata, arachnids. In: W. Westheide, R. Rieger (Ed.): Special Zoology. Part 1: Protozoa and invertebrates. Gustav Fischer, Stuttgart / Jena 1997, p. 449.
↑ Alessandro Minelli, Geoffrey Boxshall, Giuseppe Fusco: Arthropod Biology and Evolution: Molecules, Development, Morphology. Springer, 2013, ISBN 978-3-642-36160-9 , pp. 309-311.

literature

Peter Weygoldt: Chelicerata, arachnids. In: W. Westheide, R. Rieger (Ed.): Special Zoology. Part 1: Protozoa and invertebrates. Gustav Fischer, Stuttgart / Jena 2004, ISBN 3-8274-1482-2 .

Web links

Commons : Chelicerae - Collection of images, videos and audio files

[1] Chelizere. In: Duden online . Retrieved June 25, 2019 .

[Weygoldt_449-2] ↑ ^a ^b ^c ^d ^e ^f Peter Weygoldt: Chelicerata, arachnids. In: W. Westheide, R. Rieger (Ed.): Special Zoology. Part 1: Protozoa and invertebrates. Gustav Fischer, Stuttgart / Jena 1997, p. 449.

[3] Alessandro Minelli, Geoffrey Boxshall, Giuseppe Fusco: Arthropod Biology and Evolution: Molecules, Development, Morphology. Springer, 2013, ISBN 978-3-642-36160-9 , pp. 309-311.