Pygidium
The pygidium (pl.: pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is composed of fused body segments, sometimes with a tail, and separated from thoracic segments by an articulation.[1]
Chelicerates
In arachnids, the pygidium is formed by reduction of the last three opisthosomal segments to rings where there is no distinction between tergites and sternites. A pygidium is present in Palpigradi, Amblypygi, Uropygi, Schizomida, Ricinulei and in the extinct order Trigonotarbida. It is also present in early fossil representatives of horseshoe crabs.
Trilobites
In trilobites, the pygidium can range from extremely small (much smaller than the head, or cephalon) to larger than the cephalon. They can be smooth, as in order Asaphida, or spiny, as in order Lichida. They can be classified into four categories according to their relative size in comparison to the cephalon.[2]
- Micropygous – the pygidium is considerably smaller than the cephalon.
- Subisopygous – the pygidium is slightly smaller than the cephalon.
- Isopygous – the cephalon and the pygidium are more or less of equal size.
- Macropygous – the pygidium is larger than the cephalon.
They can further be subdivided in their morphological similarity to the thorax. Pygidia that are similar in shape and form to the thoracic segments are termed homonomous, while pygidia that vary significantly from the shape and form of the thoracic segments (like by the presence or absence of spines) are heteronomous.
Insects
In insects, the pygidium is the dorsal tergite of the last external abdominal segment.[3]
Other uses
Pygidium is also a superseded genus of fish of the family Trichomycteridae. Most species of this genus have been reassigned to the genus Trichomycterus. Some worms also have a pygidial appendage, like Polychaeta of the genus Ophryotrocha[4]
See also
References
- ^ Shultz, J.W. (1990). Evolutionary Morphology And Phylogeny of Arachnida. Cladistics 6: 1–38.
- ^ Samuel M. Gon III (November 12, 2009). "The Pygidium". A Guide to the Orders of Trilobites. Retrieved April 13, 2011.
- ^ G. Gordh, D. Headrick. 2003. A Dictionary of Entomology. CABI Publishing. p. 757.
- ^ https://www.researchgate.net/publication/277452269_Three_Species_of_Dorvilleidae_annelida_Polychaeta_Associated_With_Atlantic_Deep-Sea_Reducing_Habitats_With_The_Description_of_Ophryotrocha_Fabriae_New_Species
External links
Content Disclaimer
Informasi ini disarikan dari Wikipedia dan disajikan kembali untuk tujuan edukasi. Konten tersedia di bawah lisensi CC BY-SA 3.0. Kami tidak bertanggung jawab atas ketidakakuratan data yang bersumber dari kontribusi publik tersebut.
- The information displayed on this website is sourced in part or in whole from Wikipedia and has been adapted for the purpose of restating it. We strive to provide accurate and relevant information, however:
- There is no guarantee of absolute accuracy. Wikipedia is an open, collaborative project that can be edited by anyone, so information is subject to change.
- It is not intended to constitute professional advice. The content displayed is for informational and educational purposes only. For important decisions (e.g., medical, legal, or financial), please consult a professional.
- Content copyright. Wikipedia is licensed under the Creative Commons Attribution-ShareAlike License (CC BY-SA). This means that content may be reused with appropriate attribution and shared under a similar license.
- Responsible use. Any risk arising from the use of information from this website is entirely the responsibility of the user.