Chaeta
As chaeta (Greek χαίτη Chaite ), plurality Chaetae (χαῖται chaîtai ), sometimes also Seta , plurality of setae that for are polychaetes and Oligochaeta characteristic bristles at annelids referred consisting of chitin consist and pockets of the body wall - in the polychaetes to the parapodia - are formed and protrude from these to the outside.
The bristles of annelids consist of protein and sheet-like β- chitin , which are deposited by ectodermal cells in the body wall pockets known as bristle follicles and by a basal cell with many cellular runners, also known as chaetoblast. The bristles consist of an outer cortex, produced by the bristle follicle, and an inner marrow, which comes from the chaetoblast. Free spaces between the branches of the chaetoblast lead to the fact that a characteristic cavity and thus a tubular structure is also formed in the bristle. When the bristle is fully developed, the chaetoblast dies.
In the case of the polychaetes, different characteristics of the bristles are decisive for the determination of the species. Thereby, there are mostly different types of bristles on the different segments of an individual. Almost all species have non-articulated (hinge-less), pointed hair-shaped bristles, which are also known as capillaries (capillary-like bristles). They can have a smooth surface or they can be finely haired or barbed. There are also spiky, hook-shaped, hatchet-shaped, feather-like and comb-like chaetae. Many species also have two-part bristles with a joint.
Thick bristles, which serve as the inner skeleton of the parapodia in some multi-bristle bristles, are called acicula (plural aciculae).
The chaetae are an important characteristic within the annelids and give their name to the polychaeta with their numerous bristles sitting on the parapodia, as well as for the little bristle (oligochaeta), which have only a few bristles. Among the leeches (Hirudinea) only the bristle leeches (Acanthobdellida) have bristles, while the other leeches are bristleless.
The bristles support the annellids in locomotion and in the perception of mechanical stimuli. In addition, there are poisonous bristles that break off, for example, in the fire bristle worms, which serve to ward off enemies.
literature
- RA Merz, SA Woodin (2006): Polychaete chaetae: Function, fossils, and phylogeny. Integrative and Comparative Biology 46 (4), pp. 481-496.
- H. Hausen (2005): Chaetae and chaetogenesis in polychaetes (Annelida). Hydrobiologia 535/536, pp. 37-52.
- Stanley J. Edmonds: Fauna of Australia, Volume 4A. Polychaetes & Allies. The Southern Synthesis 4. Commonwealth of Australia, 2000. Class Polychaeta. Pp. 5, 71f.
Web links
- Bristles . In: Lexicon of Biology , online edition.