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A chaeta or cheta (from
Both lobes of the parapodium, the notopodium and neuropodium can bear chaetae. Chaetae on the notopodium are called notochaetae and those on the neuropodium are called neurochaetae. Thick, internal chaetae that provide support for well-developed notopodia or parapodia are called
Lepidonotus F166815 neurochaetae.png, unidentate neurochaetae from a ''Lepidonotus'' sp. specimen from Museums Victoria
Lepidonotus neuro F64528.jpg, bidentate neurochaetae from a ''Lepidonotus'' sp. specimen from Museums Victoria
A chaeta or cheta (from Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
χαίτη “crest, mane, flowing hair"; plural: chaetae) is a chitinous bristle or seta
In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
found in annelid worms, (although the term is also frequently used to describe similar structures in other invertebrates such as arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s). Polychaete annelids, ('polychaeta' literally meaning "many bristles") are named for their chaetae. In Polychaeta, chaetae are found as bundles on the parapodia
In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...
, paired appendages
An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...
on the side of the body. The chaetae are epidermal
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
extracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
structures, and clearly visible in most polychaetes. They are probably the best studied structures in these animals.
Use in taxonomy and identification
The ultrastructure of chaetae is fundamentally similar for all taxa but there is vast diversity in chaetal morphology. Moreover, chaetae bear precise characters for determination of species and taxonomic assessment. The shape, absolute and relative size, number, position, ornamentation and type are important taxonomic characters and specific types are often associated with families or genera. They are sometimes also species-specific and in some cases can be used to differentiate otherwise identical-looking species.Types of chaetae
Both lobes of the parapodium, the notopodium and neuropodium can bear chaetae. Chaetae on the notopodium are called notochaetae and those on the neuropodium are called neurochaetae. Thick, internal chaetae that provide support for well-developed notopodia or parapodia are called acicula
Acicula (singular: aciculum) are strong, stout internal chaetae that provide support to parapodia
In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protr ...
.
A wide range of chaetal shapes and arrangements exists:
Basic forms are capillaries and spines. Capillaries are the most common form of chaetae and are very thin and tapering. Spines are also common but are thicker and stouter than capillaries and may be curved or straight and can be distally dentate (e.g. unidentate or bidentate).
Furcate (also called comb, forked or brush) chaetae are similar to capillaries for most of their length but expand distally into a flattened comb- or fork-like tip.
Hooks are stout cheatae that curve distally and may be dentate or strongly curved (falcate). These chaetae may also be capped with a translucent hyaline hood.
Compound chaetae possess a joint or hinge toward the distal end that allows a distal blade or appendage to articulate around it.
Uncini are highly modified chaetae in which the shaft is reduced (or virtually absent) and the tip is broadened to create short, stout structures. These are often present in sedentary taxa.
See also
*Chaetotaxy
Chaetotaxy is the arrangement of bristles (macrochaetae) on an arthropod or annelid, or taxonomy based on their position and size. For example, it is important in Diptera, in which group it was formalised by Ernst August Girschner. The term chaeto ...
References
{{reflist Annelid anatomy