In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living .
Animal setae
Protostomes
Depending partly on their form and function, protostome setae may be called
macrotrichia,
,
scales, or
Common name, hairs. The setal membrane is not
Cuticle, so movement is possible.
Annelid setae are stiff bristles present on the body. They allow and their relatives to attach to the surface and prevent backsliding during peristaltic motion. These hairs make it difficult to pull a worm straight from the ground. Setae in oligochaetes (the group including earthworms) are largely composed of chitin.
have mechano- and chemosensory setae.
Setae on the integument of insects are unicellular, meaning that each is formed from a single epidermal cell of a type called a trichogen, literally meaning "bristle generator". They are at first hollow and in most forms remain hollow after they have hardened. They grow through and project through a secondary or accessory cell of a type called a tormogen, which generates the special flexible membrane that connects the base of the seta to the surrounding integument. Some insects, such as Eriogaster lanestris larvae, use setae as a defense mechanism, as they can cause dermatitis when they come into contact with skin.
Deuterostomes
Vertebrates
The pads on a
gecko's feet are small hair-like processes that play a role in the animal's ability to cling to vertical surfaces. The micrometer-scale setae branch into nanometer-scale projections called spatulae.
A
Tokay gecko's two front feet can sustain 20.1 N of force parallel to the surface using approximately 14,400 setae per mm
2. This equates to ~ 6.2 pN per seta, but does not sufficiently account for the overall stickiness behavior shown by the foot pads.
Classification uncertain
In 2017, a description of a new species of basal
deuterostome called
Saccorhytus was published. This animal appears to have seta in the pores along the side of its body.
However, in 2022,
Saccorhytus is considered to be an early
Ecdysozoa, and was described as having "lacked setae".
Fungal setae
In
mycology, "setae" refer to dark-brown, thick-walled, thornlike
cystidia found in
corticioid fungi and
polypores in the family
Hymenochaetaceae.
Though mainly microscopic, the setae of some species may be sufficiently prominent to be visible with a hand lens.
Plant setae
In
botany, "seta" refers to the stalk supporting the
sporangium of a
moss or
Marchantiophyta (both closely related in a clade called "Setaphyta"), and supplying it with nutrients. The seta is part of the
sporophyte and has a short foot embedded in the
gametophyte on which it is
parasitic. Setae are not present in all mosses, but in some
species they may reach 15 to 20 centimeters in height.
[ (2005): Biology of Plants (7th ed.). W.H. Freeman and Company.]
Chaetoceros setae
In the diatom family
Chaetocerotaceae, "seta" refers to the hairlike outgrowths of the valve, i.e. of the face of the cells.
[Tomas, C. R., Hasle G. R., Syvertsen, E. E., Steidinger, K. A., Tangen, K., Throndsen, J., Heimdal, B. R., (1997). Identifying Marine Phytoplankton, Academic Press.] These setae have a different structure than the valve. Such setae may prevent rapid sinking and also protect the cells from grazing.
Synthetic setae
Synthetic setae are a class of synthetic
that detach at will, sometimes called resettable adhesives, yet display substantial stickiness. The development of such synthetic materials is a matter of current research.
[ Setae Research ]
See also
