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The Acariformes, also known as the Actinotrichida, are the more diverse of the two superorders of
mite Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...
s. Over 32,000 described
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), ...
are found in 351 families, with an estimated total of 440,000 to 929,000 species, including undescribed species.


Systematics and taxonomy

The Acariformes can be divided into two main
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s – Sarcoptiformes and Trombidiformes. In addition, a
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
group containing primitive forms, the Endeostigmata, was formerly also considered distinct. The latter is composed of only 10 families of little-studied, minute, soft-bodied mites that ingest solid food, such as
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
,
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
, and soft-bodied
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
s such as
nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...
s,
rotifer The rotifers (, from Latin 'wheel' and 'bearing'), sometimes called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic Coelom#Pseudocoelomates, pseudocoelomate animals. They were first describ ...
s, and
tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them . In 1776, th ...
s. These clades were formerly considered
suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
s, but this does not allow for a sufficiently precise classification of the mites and is abolished in more modern treatments; the Endeostigmata are variously considered to form a suborder on their own (the old view) or are included mainly in the Sarcoptiformes, thus making both groups
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
. The superfamily
Eriophyoidea Eriophyoidea are a superfamily of herbivore, herbivorous mites. All post-embryonic instars lack the third and fourth pairs of legs, and the respiratory system is also absent. The taxonomy of this group has always been confused. There were famili ...
, traditionally considered members of the Trombidiformes, have been found to be basal mites in genomic analyses, sister to the clade containing Sarcoptiformes and Trombidiformes. Another group often mentioned is the Actinedida, but in treatments like the present one, this is split up between the Sarcoptiformes (and formerly the separate Endeostigmata) and Trombidiformes (which contains the bulk of the "Actinedida"), because it appears to be a massively paraphyletic " wastebin taxon", uniting all Acariformes that are not "typical" Oribatida and Astigmatina. The Trombidiformes present their own problems. The small group Sphaerolichida appears to be the most ancient lineage among them. However, the
Prostigmata Prostigmata is a suborder of mites belonging to the order Trombidiformes, which contains the "sucking" members of the "true mites" (Acariformes). Many species are notorious pests on plants. Well-known examples of prostigmatan plant parasites ...
are variously subdivided into the Anystina and Eleutherengona, and Eupodina. The delimitation and interrelationships of these groups are entirely unclear; while most analyses find one of the latter two, but not the other to be a subgroup of the Anystina; neither of these mutually contradicting hypotheses is very robust; possibly this is a simple error because phylogenetic software usually fails in handling non
dichotomous A dichotomy () is a partition of a set, partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothi ...
phylogenies. Consequently, it may be best for the time being to consider each of the three main prostigmatan lineages to be equally distinct from the other two.


Fossil record

The oldest fossils of acariform mites are from the
Rhynie Chert The Rhynie chert is a Lower Devonian Sedimentary rock, sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield ...
, Scotland, which dates to the early
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
, around 410 million years ago The
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
'' Immensmaris chewbaccei'' had idiosoma of more than in length and was the largest fossil acariform mite and also the largest erythraeoid mite ever recorded.


Diversity

The Sarcoptiformes ingest solid food, being mainly microherbivores, fungivores and
detritivore Detritivores (also known as detrivores, detritophages, detritus feeders or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...
s. Some Astigmatina – the Psoroptidia – have become associated with
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s and nest-building
insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...
s. These include the well known
house dust mite House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies. Biology Species The curren ...
s, scab mites and mange mites, stored product mites, feather mites and some fur mites. The relationships between their main groups are not well-resolved and subject to revision. In particular it appears as if the Oribatida need to be split up in two, as the Astigmatina are closer to some of them (e.g. certain Desmonomata) than the latter are to other "Oribatida". The Trombidiformes are most noted for the economic damage caused by many
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...
species. All of the most important plant
pests PESTS was an anonymous American activist group formed in 1986 to critique racism, tokenism, and exclusion in the art world. PESTS produced newsletters, posters, and other print material highlighting examples of discrimination in gallery represent ...
among the
Acari Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as ea ...
are trombidiformans, such as spider mites (Tetranychidae) and Eriophyidae. Many species are also predators, fungivores, and animal parasites. Some of the most conspicuous species of free-living mites are the relatively large and bright red velvet mites, that belong to the family
Trombidiidae Trombidiidae, also known as red velvet mites, true velvet mites, or rain bugs, are small arachnids (eight-legged arthropods) found in plant litter and are known for their bright red color. While adults are typically no more than in length, so ...
. Oribatid mites and to a much lesser extent others are a source of alkaloids in poison frogs (namely small species like the strawberry poison-dart frog ''Oophaga pumilio''). Such frogs raised without these oribatids in their diets do not develop the strong poisons associated with them in the wild.


Parthenogenesis

Acariformes species appear to have evolved from a sexual ancestor and the primary manner of reproduction during the course of evolution has been
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
. However, within the super order Acariformes,
parthenogenetic Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means the development of an embryo from an unfertiliz ...
species have arisen numerous times during the course of evolution. In contrast to the commonly held view that parthenogenetic lineages are short lived, four species-rich parthenogenetic clusters of the order Oribatida are very ancient and likely arose 400-300 million years ago. In some parthenogenetic species that undergo
automixis Automixis is the fusion of (typically haploid) nuclei or gametes derived from the same individual. The term covers several reproductive mechanisms, some of which are parthenogenetic. Diploidy might be restored by the doubling of the chromosomes ...
(a kind of self-fertilization that retains
meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
) sexual reproduction has re-emerged.


Examples

Eriophyidae, plant
parasites Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...
, e.g. '' Acalitus essigi'' (redberry mite) ; Sarcoptiformes * Cheese mites * Epidermoptidae * Gastronyssidae *''
Sarcoptes scabiei ''Sarcoptes scabiei'' (/sɑː''r''ˈkɒptiːz skeɪˈbiːaɪ/ Traditional English pronunciation of Latin) or the itch mite is a parasite, parasitic mite found in all parts of the world that burrows into skin and causes scabies. Humans become Inf ...
'' ; Trombidiformes * Demodecidae, e.g. ''Demodex'' mites * Erythraeidae * Labidostommatidae *'' Polydiscia deuterosminthurus'' * Smarididae * Spider mites, e.g. '' Tetranychus urticae'' * Tarsonemidae, a number of which are plant
pests PESTS was an anonymous American activist group formed in 1986 to critique racism, tokenism, and exclusion in the art world. PESTS produced newsletters, posters, and other print material highlighting examples of discrimination in gallery represent ...
, e.g. '' Acarapis woodi'' * Tydeidae


References


Further reading

* {{Authority control Arthropod superorders