biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

, setae (; seta ; ) are any of a number of different bristle- or

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and ...

-like structures on living

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

Animal setae

Protostomes

Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae,

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

, or informally, hairs. The setal membrane is not cuticularized, so movement is possible.

Annelid The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...

setae are stiff bristles present on the body. They allow

earthworm An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass, depending on the author) Oligochaeta. In classical systems, they we ...

s and their relatives to attach to the surface and prevent backsliding during

peristaltic Peristalsis ( , ) is a type of intestinal motility, characterized by symmetry in biology#Radial symmetry, radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an wikt:anterograde, anterograde dir ...

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 Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...

. They are classified according to the limb to which they are attached; for instance, notosetae are attached to

notopodia In invertebrates, the term parapodium (Greek language, Gr. ''para'', beyond or beside + ''podia'', feet; : parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in Annelid, annelids, where they ar ...

; neurosetae to neuropodia. The setae on polychaete worms are referred to as chaeta due to their differing morphology.

Crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

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 ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

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, Exoskeleton, shell, germ or Peel (fruit), rind. Etymology The term is derived from ''integumentum'', which is Latin for "a coverin ...

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

. 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. Diptera setae are bristles present throughout the body and function as mechanoreceptors.

Deuterostomes

Vertebrates

The pads on a

gecko Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates. They range from . Geckos are unique among lizards ...

's feet are small hair-like

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management * Business process, activities that produce a specific s ...

es 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 mm². 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 ecdysozoan, and was described as having "lacked setae".

Fungal setae

mycology Mycology is the branch of biology concerned with the study of fungus, fungi, including their Taxonomy (biology), taxonomy, genetics, biochemistry, biochemical properties, and ethnomycology, use by humans. Fungi can be a source of tinder, Edible ...

, "setae" refer to dark-brown, thick-walled, thornlike cystidia found in corticioid and poroid fungi in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Hymenochaetaceae The ''Hymenochaetaceae'' are a family (biology), 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 disea ...

. Though mainly microscopic, the setae of some species may be sufficiently prominent to be visible with a hand lens.

Plant setae

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

, "seta" refers to the stalk supporting the capsule of a

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

liverwort Liverworts are a group of non-vascular land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry ...

(both closely related in a clade called "Setaphyta"), and supplying it with nutrients. The seta is part of the

sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...

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 se ...

on which it is parasitic. Setae are not present in all mosses, but in some

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

they may reach 15 to 20 centimeters in height.

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 Synthetic setae emulate the setae found on the gecko feet, toes of a gecko and scientific research in this area is driven towards the development of Dry glue, dry adhesives. Geckos have no difficulty mastering vertical walls and are apparently cap ...

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

References

{{reflist, 28em Plant anatomy Animal hair Fungal morphology and anatomy