In
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, setae (singular seta ; from the Latin word for "
bristle") are any of a number of different bristle- or
hair-like structures on living
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...
s.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. They help, for example,
earthworms 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 (a group including earthworms) are largely composed of
chitin. They are classified according to the limb to which they are attached; for instance, notosetae are attached to
notopodia; neurosetae to
neuropodia.
Crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s have mechano- and chemosensory setae.
Setae are especially present on the mouthparts of crustaceans
and can also be found on grooming limbs.
In some cases, setae are modified into scale like structures.
Setae on the legs of
krill
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish.
Krill are consi ...
and other small crustaceans help them to gather
phytoplankton. It captures them and allows them to be eaten.
Setae on the
integument
In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind.
Etymology
The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...
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
In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind.
Etymology
The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...
. Depending partly on their form and function, setae may be called hairs, macrotrichia,
chaetae, or
scales. The setal membrane is not cuticularized and movement is possible. 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.
* Gekko's seta: According to Kellar Autumn, "Two front feet of a tokay gecko (''
Gekko gecko'') can withstand 20.1 N of force parallel to the surface with 227 mm
2 of pad area (Irschick et al. 1996). The foot of a tokay bears approximately 3600 tetrads of setae per mm
2, or 14,400 setae per mm
2 (Schleich and Kastle 1986; pers. obs.). Consequently, a single seta should produce an average force of 6.2 pN, and an average shear stress of 0.090 N⋅mm
−1 (0.9 atm). However, single setae proved both much less sticky and much more sticky than predicted by whole animal measurements, under varying experimental conditions, implying that attachment and detachment in gecko setae are mechanically controlled (Autumn et al. 2000)."
Classification uncertain
In 2017, a description of a new species of basal
deuterostome called ''
Saccorhytus
''Saccorhytus'' (from Latin ''saccus'' "bag" and Ancient Greek ῥύτις ''rhytis'' "wrinkle") is an extinct genus of animal possibly belonging to the superphylum Ecdysozoa, and it is represented by a single species, ''Saccorhytus coronarius'' ...
'' 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
ecdysozoan, and was described as having "lacked setae".
Fungal setae
In
mycology, "setae" refer to dark brown, thick-walled, thorn-like
cystidia
A cystidium (plural cystidia) is a relatively large cell found on the sporocarp of a basidiomycete (for example, on the surface of a mushroom gill), often between clusters of basidia. Since cystidia have highly varied and distinct shapes that ar ...
found in
corticioid
The corticioid fungi are a group of fungi in the Basidiomycota typically having effused, smooth basidiocarps (fruit bodies) that are formed on the undersides of dead tree trunks or branches. They are sometimes colloquially called crust fungi or pa ...
and
poroid fungi in the
family Hymenochaetaceae
The ''Hymenochaetaceae'' are a family of fungi in the order Hymenochaetales. The family contains several species that are implicated in many diseases of broad-leaved and coniferous trees, causing heart rot, canker and root diseases, and also es ...
. Though mainly microscopic, the setae of some species may be sufficiently prominent to be visible with a hand lens.
Plant setae
In
botany
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
, "seta" refers to the stalk supporting the
capsule of a
moss or
liverwort
The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...
(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
A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...
on which it is
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
. Setae are not present in all mosses, but in some
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
they may reach 15 to 20 centimeters in height.
Chaetoceros setae
In the diatom family
Chaetocerotaceae
Chaetocerotaceae is a diatom family ( Bacillariophyta). This family comprise the three genera ''Attheya'' T. West, '' Bacteriastrum'' Shadbolt and ''Chaetoceros'' Ehrenberg. ''Chaetoceros'' is perhaps the largest and most species rich genus of m ...
, "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
adhesives 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
*
Chaeta
*
Synthetic setae
*
Van der Waals force
References
{{reflist, 28em
Plant anatomy
Animal hair
Fungal morphology and anatomy