The Protura, or proturans, and sometimes nicknamed coneheads,
are very small (0.6-1.5mm long), soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. The Protura constitute an
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
of
hexapods that were previously regarded as insects, and sometimes treated as a
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differently ...
in their own right.
[
Some evidence indicates the Protura are basal to all other hexapods,] although not all researchers consider them Hexapoda
The subphylum Hexapoda (from Greek for 'six legs') comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura (all of these were once considere ...
, rendering the monophyly
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...
of Hexapoda unsettled. Uniquely among hexapods, proturans show anamorphic development, whereby body segments are added during moults.
There are close to 800 species, described in seven families. Nearly 300 species are contained in a single genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
, ''Eosentomon
''Eosentomon'' is a genus of proturans in the family Eosentomidae
The Eosentomidae are a family of hexapods in the order Protura
The Protura, or proturans, and sometimes nicknamed coneheads, are very small (0.6-1.5mm long), soil-dwelling ani ...
''.
Morphology
Proturans have no eyes, wings, or antennae, and, lacking pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
ation, are usually white or pale brown. The sensory function of the antennae is fulfilled by the first of three pairs of five-segmented legs
A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element c ...
, which are held up, pointing forward and have many tarsal sensilla and sensory hairs. They walk with only four legs. The head is conical, and bears two pseudoculi with unknown function. The body is elongated and cylindrical, with a postanal telson
The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on acco ...
at the end. The mouthparts
Mouthparts may refer to:
* The parts of a mouth
** Arthropod mouthparts
The mouthparts of arthropods have evolved into a number of forms, each adapted to a different style or mode of feeding. Most mouthparts represent modified, paired append ...
are entognathous (enclosed within the head capsule) and consist of thin mandibles and maxillae. There are no cerci at the end of the abdomen, which gives the group their name, from the Greek ''proto-'' (meaning "first", in this case implying primitive), and ''ura'', meaning "tail". The first three abdominal segments bear short limb-like appendage
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 ante ...
s called "styli". First pair of styli is two-segmented, while the second and third pair are two-segmented or unsegmented. The genitalia
A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
are internal and the genital opening lies between the eleventh segment and the telson of the adult. The genitalia are everted from a chamber in both sexes. Only the two families Eosentomidae
The Eosentomidae are a family of hexapods in the order Protura
The Protura, or proturans, and sometimes nicknamed coneheads, are very small (0.6-1.5mm long), soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. ...
and Sinentomidae
''Sinentomon'' is the only genus in the family Sinentomidae, in the hexapod order Protura
The Protura, or proturans, and sometimes nicknamed coneheads, are very small (0.6-1.5mm long), soil-dwelling animals, so inconspicuous they were not notic ...
possess a simple tracheal system with a pair of spiracles on both mesothorax and metathorax (but never on the abdomen), while those in the other families lack these structures and perform gas exchange
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...
by diffusion
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
.
Ecology
Proturans live chiefly in soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
, moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ...
es, and leaf litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...
of moist temperate forests that are not too acidic. They have also been found beneath rocks or under the bark
Bark may refer to:
* Bark (botany), an outer layer of a woody plant such as a tree or stick
* Bark (sound), a vocalization of some animals (which is commonly the dog)
Places
* Bark, Germany
* Bark, Warmian-Masurian Voivodeship, Poland
Arts, e ...
of trees, as well as in animal burrows. They are generally restricted to the uppermost , but have been found as deep as . Although they are sometimes considered uncommon, they are probably often overlooked because of their small size: densities of over 90,000 individuals per square metre have been measured.
The diet of proturans is not yet sufficiently observed, but they feed on mycorrhizal fungi, dead Acari
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
, and mushroom powder in culture, and are thought to feed on decaying vegetable matter and fungi in the wild. The styliform mouthparts suggest the Protura are fluid feeders, with evidence that some species suck out the contents of fungal hyphae.
Proturans which live near the soil surface generally have one generation per year and have longer legs, while those that live deeper have shorter legs and reproduce less seasonally, although some migratory species move to deeper layers for the winter and shallower layers for the summer.
Development
The nymph
A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ...
has 8 abdominal segments plus telson, but the number increases through moulting
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
until the full adult number of 11 is reached. Further moults may occur, but do not add any more body segments, and it is not known whether the adults continue to moult through their lives. Eggs have only been observed in a few species. Five developmental stages follow: the prenymph hatches from the egg and has only weakly developed mouthparts and 8 abdominal segments; nymph I follows and has fully developed mouthparts; nymph II has 9 abdominal segments; maturus junior has 11 abdominal segments and is followed by the adult. The family Acerentomidae differs in having an extra preimago stage, with partially developed genitalia, between the maturus junior and the adult.
History
Proturans were first discovered in the early 20th century, when Filippo Silvestri and Antonio Berlese discovered the animals independently. The first species to be described was '' Acerentomon doderoi'', published in 1907 by Silvestri, based on material from near Syracuse, New York
Syracuse ( ) is a city in and the county seat of Onondaga County, New York, United States. It is the fifth-most populous city in the state of New York following New York City, Buffalo, Yonkers, and Rochester.
At the 2020 census, the city' ...
.
Impact on humans
Proturans aid in decomposition by helping in the breakdown of leaf litter and recycling organic nutrients back into the soil. They thus play a role in soil formation and composition, which can be vital in soil restoration.
References
External links
*
*
Proturans
on the University of Florida
The University of Florida (Florida or UF) is a public land-grant research university in Gainesville, Florida. It is a senior member of the State University System of Florida, traces its origins to 1853, and has operated continuously on its ...
/ Institute of Food and Agricultural Sciences
The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is a teaching, research and Extension scientific organization focused on agriculture and natural resources. It is a partnership of federal, state, and county governmen ...
''Featured Creatures'' website
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Arthropod orders
Taxa described in 1907
Taxa named by Filippo Silvestri