The segmentation of many organisms, i. H. the division of the body into primarily similar ( homologous and analogous ) sections is a result of pattern formation processes in the embryonic stage (→ morphogenesis ). Segmentation is particularly noticeable in worms (e.g. earthworm ) and arthropods (e.g. millipedes ).
Mostly, segmentation can be observed during early ontogenesis , after which the body segments often fuse together.
In beltworms , segmentation is traced back to a kind of "budding": early divisions of the flatworm embryo give rise to teloblast cells, which are stem cells that divide asymmetrically.
In insects , segmentation is particularly evident in the early larval stages. All vertebrates , too, have a fundamentally segmental structure (e.g. somites , vertebrae or ribs with nerves and blood vessels in between). The zebrafish is the preferred object for studying segmentation in vertebrates.
In many groups of animals, e.g. B. in arthropods, individual segments are fused into body sections, the Tagmata . Secondarily, individual segments can experience functional differentiation in the course of phylogenesis ( homology but no analogy ).
The individual segments are also called metamers . However, metamerism is not completely synonymous with segmentation, but a distinction is made between coelomatic metamerism ( coelom structured), homonomic metamerism (segments of the same shape) and heteronomous metamerism (segments shaped differently).
Segmentation in plants is mainly found in lower and higher algae .
- ↑ GE Budd: Why are arthropods segmented? In: Evolution and Development . tape 3 , no. 5 , 2001, p. 332 , doi : 10.1046 / j.1525-142X.2001.01041.x .
- ^ D. Tautz : Segmentation. In: Dev Cell. Volume 7, No. 3, 2004, pp. 301-312. doi: 10.1016 / j.devcel.2004.08.008 . PMID 15363406 .
- ^ AD Peel, AD Chipman, M. Akam: Arthropod Segmentation: Beyond The Drosophila Paradigm. In: Nat. Rev. Genet. Volume 6, No. 12, 2005, pp. 905-916. doi: 10.1038 / nrg1724 . PMID 16341071 .
- ↑ O. Cinquin: Understanding the somitogenesis clock: what's missing? In: Mech. Dev. Volume 124, No. 7-8, 2007, pp. 501-517. doi: 10.1016 / j.mod.2007.06.004 . PMID 17643270 .