right|thumb|upright|[[Earwig with large cerci (top)]]

Cerci (: cercus) are paired appendages usually on the rear-most segments of many arthropods, including insects and symphylans. Many forms of cerci serve as sensory organs, but some serve as pinching weapons or as organs of copulation. It is not clear that other structures so named are homologous. In the Symphyla they are associated with spinnerets.

Morphology and functions

Most cerci are segmented and jointed, or filiform (threadlike), but some take very different forms. Some Diplura, in particular Japyx species, have large, stout forcipate (pincer-like) cerci that they use in capturing their prey.

The Dermaptera, or earwigs, are well known for the forcipate cerci that most of them bear, though species in the suborders Arixeniina and Hemimerina do not. It is not clear how many of the Dermaptera use their cerci for anything but defense, but some definitely feed on prey caught with the cerci, much as the Japygidae do.

Some hexapods such as mayflies, silverfish and diplurans possess an accompanying third central tail filament which extends from the tip of the abdomen. This is referred to as the terminal filament and is not regarded as a cercus.

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File:Pamphagidae Hoplolopha abdomen cerci IMG 0862s.JPG|Short cerci on abdomen of a species of pamphagid grasshopper

File:Lepismatidae Ctenolepisma longicaudata 9815s.jpg|Long sensory cerci on Ctenolepisma, flanking the median cerciform appendage and paired stylets

File:Diplura Campodea Japyx.jpg|Two forms of Diplura, illustrating cerci with sensory glandular function, as contrasted with forcipate forms of cerci used in predation

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References

  • University of Sydney Biology Dept