ACARI | Oribatida

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The Oribatida suborder includes tiny, well-armoured, hard-bodied, mostly dark-coloured, free-living mites that predominantly inhabit woodland areas where they live in the soil and leaf-litter feeding on decaying material and fungi. In this type of habitat, many species may also be found on fallen rotting deadwood, especially on the underside of small branches laying directly

on the ground, which is certainly where I've had most success photographing them. But they don't all live at ground level

and, although far more difficult to locate, it should be remembered that some species are arboreal occurring on tree trunks, lichens or amongst mosses. And, of course, they're not restricted to woodland either, as they can also be found in gardens and various other environments including wetlands.

Most oribatids have an overall body length in the region of 300-700µm which, even at the top end, is pushing the boundaries in respect of trying to locate and photograph them in their natural habitat. However, there are few better known species which are fortunately a tad larger that obviously provide better and more realistic photo opportunities in certain situations. It's hard

to gauge their size, but I'd say that virtually all of the individuals featured here range from maybe 700 or 800µm, up to 1.5mm, possibly even a fraction more and, therefore, a little easier to spot with the naked eye. They're still a challenge, but one of the attributes of oribatid mites, apart from the variety, is that when you do find them, they're invariably sitting still or moving around relatively slowly.

Their body is protected by sclerotised plates, with adults typically having two covering the dorsum, one at the front and one

at the rear, plus a varying arrangement of smaller plates on the underside. The anterior dorsal plate is called the prodorsum and is usually connected in some manner to the ventral plates, although with the ptychoid mites that can roll themselves up into a ball, it is isolated and alternatively known as the aspis. Effectively the prodorsum covers the front part of the mite, which is the gnathosoma and the leading edge of the notogaster (a defined part of the body called the proterosoma) and often projects forward such that the gnathosoma is hidden when viewed from above. The extended portion of the prodorsum is the rostral tectum, or simply rostrum. The larger dorsal plate, called the notogaster, protects the main part of the body

(an area called the hysterosoma) and sits directly behind the anterior plate with the flexible, non-hardened zone between, if present, known as the sejugal furrow. Some species that do not have the ability to roll up, have lateral plates that help to protect their legs, called pteromorphs, which can be barely visible or well-defined, such as in the Galumnidae family.

That's a simple, generalised description, but it helps to explain that oribatid mites have different body forms; dichoid where the sejugal furrow, which runs round the body between the second and third pairs of legs, is flexible allowing free movement between the protersoma and hysterosoma; ptychoid when the ventral plates are adapted so that the legs can be withdrawn, which allows the mite to retract its anterior dorsal plate effectively forming a protective ball that can be likened to the way a hedgehog rolls up; and holoid where the ventral surface is fused, such that articulation of the body is pretty much restricted to side to side movement.

A few other features to note are that oribatid mites do not have eyes, so to aid navigation and detecting movement, they have a pair of adapted sensory setae known as the sensillus that are shaped like feathers, clubs or simple bristles that arise from pits (bothridia) on the front of the prodorsum. Many species have a pair of conspicuous blade-like structures than run down the prodorsum called lamellae that usually end in a projecting cusp. The structure and form of the lamellae vary but, together with associated features such as the interlamellar setae, are important identifying characters that should be visible in photos to some degree.

The latest information at the time of writing confirms that, excluding Astigmata (see below), just over 400 species of oribatid mites have been recorded in Britain. I haven't reconciled the actual number with the listing on the Soil Biodiversity website, but assuming the data aligns, those species are in 155 genera, separated into 67 families.

During the course of putting this section together I made a concerted effort in looking for some of the species I wanted to include and am rather pleased that I was quite successful as I'm currently able to feature 18 species or genera from 14 different families. They are shown below in their listed systematic (hierarchal alphabetic) order with a header showing the full classification and with various accompanying notes regarding identification or, indeed, any other bits of information that I think could be interesting or useful in the future.

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Poronoticae > Ceratozetoidea > Euzetidae

It's quite appropriate that the first species featured here is Euzetes globulus as it's regularly credited as being one of the most photographed oribatid mites due to its size and shiny appearance, which apparently makes it stand out, and the fact that it's supposedly very common.

I'm not sure I'd agree because, even if they are common, which I would question, I wouldn't say they're particularly easy to find despite being in the region of 1-1.2mm long. That might be considered large for a mite, but they're still tiny. Yes, they're shiny, which certainly makes them easier to spot, but the downside of having a hard reflective surface is that they're tricky to photograph with flash. It's fine to have a bit of a highlight, but not a large blown-out patch. You need low flash power, a good diffuser and the right angle and, dare I say, you also need to see them on deadwood or in litter rather than on the ground as you'll struggle to get a decent shot of any dark-coloured mite on soil.

They have a certain look about them that has resulted in various common names, such as the 'black helmet mite' which is a pretty good description, except that they're very dark brown, rather than black. If you find an individual that's more of a reddish-brown colour it's either freshly moulted or possibly another species. The front rim of the 'helmet' has a distinctive shape and the pronotum, which has a pair of lamellae with setae arising from the ends of free cusps, is rather short and barely visible when viewed from above.

Euzetes globulus is the sole member of the Euzetidae family.

Euzetidae > Euzetes globulus

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Poronoticae > Galumnoidea > Galumnidae

Although Galumnidae includes eight species in four genera that can't be identified from photos, the family itself can be distinguished by the large pteromorphs which extend forward, more than backwards, from their point of attachment. These 'lobe-like' shields that help to protect the mite's legs are also present in Euzetes globulus, but are continuous with the body and barely noticeable which is much the case with many other species in the Poronoticia parvorder, whereas in Galumnidae they're particularly well-developed.

Galumnidae > undetermined species

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Poronoticae > Oribatelloidea > Achipteriidae

The Achipteriidae family includes twelve species in four genera, which are broadly distinguished by having a prodorsum with lamellae that are either closely adjacent or fused medially, and/or linked with well-developed translamella, notogaster including fixed pteromorphs that bear forward-pointing prongs, and genu IV longish and conspicuously bent inwards.

As far as I can ascertain, the individual currently featured here is Achipteria nitens, which is a tad larger than the more common species Achipteria coleoptera, at 600-800µm with a slightly more elongate shape and with much longer notogastral setae. Otherwise described as dark brown, sometimes yellowish, with a smooth, rounded body; notogaster longer than wide with minute granular cerotegument (waxy covering); pteromorphs with a knife-like tip; rostrum pointed when viewed both dorsally and laterally; lamellae fused medially, but with the cusps well separated; interlamellar setae long and thin; rostral setae long and extending beyond the tip of the rostrum.

Achipteriidae > Achipteria nitens

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Poronoticae > Oripodoidea > Oribatulidae

Oribatulidae includes 15 species in three genera, Oribatula, Phauloppia and Zygoribatula but, as far as I can ascertain, the only member of the family that you're likely to find and be able to photograph is probably Phauloppia lucorum. It's the largest species at around 600-900µm and is reasonably easy to distinguish; having a brown body comprising a well-rounded, finely punctured notogaster covered with fourteen pairs of long, slightly curved setae, and a pronounced prodorsum that has very thin, barely discernable, centrally located lamellae, and short sensillus. They're an arboreal mite, particularly associated with lichens and decaying mosses on trees.

Phauloppia nemoralis and rauschenensis are smaller (>600µm) and have shorter body setae, while Phauloppia pilosa is smaller still (>500µm) with much longer setae.

[Phauloppia lucorum is often cited alongside Lucoppia burrowsi, a similar species that occurs in Europe. It's not listed as being recorded in Britain, but I have seen it mentioned, so whether it's possibly a new species I'm not sure. Alternatively, it may just be a synonym of another species given that Phauloppia lucorum was formerly named Lucoppia lucorum].

Oribatulidae > Phauloppia lucorum

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae >

Carabodoidea > Carabodidae | Cepheoidea > Cepheidae | Cymbaeremoidea > Cymbaeremaeidae

I've lumped the following species and their associated families together despite the fact that they're taxonomically separated because, to my eyes at least, they look superficially similar at first glance and are often found together. Obviously, they're distinguishable once you're able to focus on them properly through the viewfinder, and I guess that in time I'll pick up on finer details such as the way they behave but, at present, one tiny black dot looks pretty much like another when searching, despite the differences that can clearly be seen in photos.

Fortunately, I'm not breaking the taxonomic sequence as the respective superfamily groups where these families are classified sit alongside each other so, from that respect alone, the species are related.

Carabodidae is placed within the Carabodoidea together with a small family Tectocepheidae. There are 14 species in two genera, Carabodes and Odontocepheus, with all but one in the former. Although Odontocepheus elongatus can be distinguished as it has four long, forward-pointing setae along the front edge, the various Carabodes species can't be reliably determined from photos as you need to closely examine the sculpturing of both the notogaster and pronotum, and probably the distribution of setae.

They are pretty much characterised by their large and broad pronotum, which is around half the length of the notogaster. That detail alone gives them a very distinctive appearance. The chunky body form gives the impression that they're relatively large by mite standards, but they're not. In fact, they're pretty much the same size as the other species I grouped together here, averaging around 500-700µm long, but with some species as small as 300µm.

With antennae and eyes, they would pass for a tiny black carabid ground beetle, hence the scientific names Carabus, and here Carabodes, coming from the Greek word 'karabos', which means beetle, but with the added 'odes' suffix, to confirm the similarity.

They can often be found on rotting deadwood in the company of other species, especially Cepheus as featured below, but also on mosses and lichens growing on trees. I've also found on them in relatively large numbers feeding on wood fungi.

Carabodidae > Carabodes sp.

Although I know that it's highly unlikely that enough detail could be captured in a photograph taken in the field, it is interesting to note the different sculpturing on both the prodorsum and notogaster, and any other specific features that can be seen such as the appearance of any notogastral setae. I'm not going to read too much into it, but even from the photos featured here there are at least two different species. Records are almost non-existent so I don't have very little information regarding the species that are likely to be seen, but I am aware that there are only a few that grow in excess of 600µm, which is a sort of guideline for the smallest mites that I'm likely to try to photograph and, quite frankly, that's pushing the boundaries. I did find a list of characters that was put together for carabodids that have been recorded in Eastern Europe, which is interesting as it covers most of the British species. The details for the four largest species are:

Carabodes coriaceus - 565-725µm, prodorsal area with two chitinized elevations and notogaster with irregular ridges (I've also read that this species has a wide cleft between the back of the pronotum and the notogaster); Carabodes femoralis - 600-715µm, prodorsal area with fine ridges and notogaster with longitudinal ridges and annulation; Carabodes rugosior - 520-650µm, prodorsal area with two tubercles in the posterior part and the notogaster with one long and several irregular ridges; and, Carabodes areolatus - 480-615µm, prodorsal area and the notogaster with areolate sculpturing. Carabodes affinis, labirinthicus and marginatus come up in searches, but they're smaller species averaging around 450-550µm.

Carabodidae > Carabodes cf.coriaceus

Carabodidae > Carabodes sp.

Cepheidae is in its own superfamily Cepheoidea. There are only eight species, but they're placed in five genera; Cepheus, Conoppia, Ommatocephus, Protocephus and Tritegeus. They are distinguished in part by having a well-defined dividing line between the prodorsum and notogaster, and a body that has knobbly or densely networked sculpturing on the dorsal surface or rough sculpturing restricted to the sides.

The Cepheus genus includes four reddish-brown species that have an almost round, slightly flattened, strongly sculptured dark-coloured back with an edge border. The rostrum is covered by large lamellae that near enough meet at the cusps. They're relatively easy to recognise, but can only be identified properly under a microscope.

That said, Cepheus cepheiformis is regarded as the 'type species' and the one that's usually cited due to its attractive juveniles which carry the exuviae of proceeding moults on their back, best seen at the deutonymph stage as they would normally have both the larvae and protonymph remains radiating out in a leaf-like pattern.

They are only 400-600µm long and pretty much colourless and, consequently, near impossible to see with the naked eye.

Cepheidae > Cepheus sp. (nymph)

Fortunately, the adults are a tad larger averaging around 600-750µm long and 400-500µm wide. You'll most likely find them in woodland and forest clearings on fallen, rotting deadwood. They are slow moving, incredibly difficult to spot on dark wood and, in my opinion, an absolute bugger to photograph.

Cepheidae > Cepheus sp.

Cymbaeremaeidae includes a single, easily recognisable species Cymbaeremaeus cymba, which one well-known acarologist aptly describes as looking like a "flat-topped raisin with a wrinkly face". It is placed within the Cymbaeremoidea superfamily together with another small family Micreremidae with just two species. It is most often found on trees amongst moss or lichens, but my encounters to date are where I've found an individual within a mixed community of other mites including the two previously mentioned species and, occasionally, some of those featured below.

Cymbaeremaeidae > Cymbaeremaeus cymba

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae > Damaeoidea > Damaeidae

Oribatid mites have many different body forms, but none look like the typical members of this family that you find crawling through leaf-litter or over rotting deadwood on their long, rather spindly legs. Although somewhat variable in size and general appearance to some degree, they're pretty much unmistakeable. The notogaster is well rounded, almost globular, and is well differentiated from the triangular-shaped prodorsum. They're generally dark-coloured in varying shades of brown or grey, to almost black. Smaller species tend to be lighter, but they shouldn't be confused with the many nymphs you'll regularly come across.

The Damaeidae family is represented in Britain by 16 species that are usually placed in eight genera or, sometimes, in a lesser number with sub-genera. They can't be specifically identified without sticking them under a microscope and pain- stakingly counting setae on certain parts of the legs and checking whether they have tiny spines on the front edge of the notogaster, so the common practice, it seems, is to simply refer to photographed individuals as Damaeus / Belba sp.

They are the two primary genera with the others having names such as Epidameous, Kunstidameous or Damaeobelba, Metabelba etc., which I suspect are alternatively regarded as subgenera.

Damaeidae > Damaeus / Belba sp.

As a consequence of their diet compared with their predacious relatives, most oribatids grow slowly and take a relatively long time to fully develop, which leaves the nymphs particularly at risk of being attacked and eaten as their protective exoskeleton is shed between growth stages. Not to be outdone by the various defence mechanisms that the adults have developed in addition to the protection given by their body plates, such as having pteromorphs to shield their legs or the ability to roll up, nymphs of a number of species, but particularly members of this family, have their own strategy as they are often seen wearing their moulted body parts as armour. It looks bizarre, but it's remarkably effective as it provides a degree of protection as well as acting as camouflage and making the nymph look much larger than it is. Some adults also adopt this tactic by using various bits of debris.

Damaeidae > Damaeus / Belba sp.

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae > Gustavioidea > Liacaridae

The Liacaridae family includes nine species in five genera, which are characterised in part by having a rounded shape and a small and somewhat pointed prodorsum with converging lamellae that in the species featured here are fused apically.

The Liacarus genus is represented in Britain by four species. They are rather variable and, as such, the identity of the smart little brown specimen featured here is tentative. It's probably Liacarus coracinus, but that assessment is pretty much based on its general appearance as the primary contenders Liacarus nitens and Liacarus subterraneus have slightly different body shapes and certain features that you should be able to see. They are also slightly larger, averaging nearer to 1200µm, whereas Liacarus coracinus is in the region of 700-900µm. If I manage to find one of those two, I will research further and update the account accordingly , but for now I'm happy that at least I've got a few reasonable photos of this individual. The remaining member of the genus is Liacarus xylariae, but I don't have any information about that species. The same with Dorycranosus splendens, which I believe is superficially similar, albeit darker, but certainly another liacarid that perhaps needs to be considered.

Liacaridae > Liacarus cf.coracinus

We then have the two Xenillus species, Xenillus clypeator and Xenillus tegeocranus, which are rather nice mites to photograph as they are a tad larger than most of the other oribatids they often hang out with.

The more common species is Xenillus tegeocranus, which I thought could be distinguished quite easily as they are typically darker than Xenillus clypeator with the notogaster having a slightly rougher and duller texture. The pronotum also looks to have a slightly different shape with the lamellae wider spaced, although that's purely my interpretation, not an official feature of the species. Xenillus clypeator on the other hand has a different appearance to my eyes as the individuals I've seen have been much paler - distinctly mid-brown rather than dark brown - with the notogaster appearing shiny with a smoother texture. They also have shorter, slightly clubbed, sensillus, whereas in Xenillus tegeocraus they're noticeably longer, and never have any conspicuous interlamellar setae.

The problem, is that Xenillus tegeocranus does have interlamellar setae just in front of the dorsal transverse line between the prodorsum and the notogaster which, unlike the sensillus, is very difficult to capture in photos. Personally, I'm not too bothered as the general appearance alone should be sufficient, but it's an important distinguishing feature that would need to be visible for recording purposes.

Liacaridae > Xenillus clypeator

Liacaridae > Xenillus tegeocranus

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae > Gustavioidea > Peloppiidae

Closely allied to the Liacaridae, the Peloppiidae family is only represented in Britain by two species, Ceratoppia bipilis and Ceratoppia sexpilosa. They are around 700-900µm long with a reddish to dark-brown colouration, a notogaster that is shiny and rounded posteriorly, and a triangular projecting prodorsum bearing lamellae ridges that extend into long horns, tipped with setae. The sensillus are long, and the interlamellar bothridial setae are very long and bristly.

Although Ceratoppia bipilis (including associated subspecies) appears to be the common form, I believe that the individual featured here is Ceratoppia sexpilosa as it has three pairs of long, conspicuous posterior notogastral setae, whereas Ceratoppia bipilis only has two. Initially I wasn't sure that I was interpreting the arrangement correctly, but I've now seen a diagram showing the location of the additional pair at position h1 which are in addition to the lower pairs at p2 and p3. They are very clearly visible in at least one of these photos.

Unfortunately, my current experience of the species is limited to one short encounter when I found this particular specimen on the underside of a piece of deadwood in a dry, but seasonally wet, area of the New Forest. Despite its tiny size, it managed to scurry away and hide remarkably quickly, giving me very little time to react. Hopefully, I'll get another opportunity at some point, but at least these photos show the important distinguishing features noted above.

Peloppiidae > Ceratoppia cf.sexpilosa

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae > Hermannielloidea > Hermanniellidae

Meet Herman, a somewhat variable, but rather distinctive little mite that always seems to be on a mission. When I found my first colony of these foraging on a piece of deadwood, I assumed that there were two species due to quite a distinct colour difference with some of the paler individuals looked rather unkempt compared with their darker relatives.

Subsequent research quickly revealed that there are indeed two species on the British list, Hermanniella granulata and a much rarer form Hermanniella punctulata, so it's pretty safe to assume that they're all the common species. And the reason for the variable appearance is that the remains of the tritonymphal exuvia adheres very closely and takes a while to wear off, which explains why some individuals look as though they're moulting.

They average around 650-850µm long and, from my experience, are extremely difficult to photograph due to a combination of their size and that they're invariably on the move, which never seems to be in a straight line. You work out which way they're headed, then faff around getting in position and, as soon as you think you've acquired focus, they do a U-turn or head off in a completely different direction. But there's no denying the fact that Herman has got real character, so you just need to persevere despite the frustration.

I love their large bothridia that can easily be mistaken for a pair of goggle-eyes, which together with the very conspicuous interlamellar setae and the presence of projecting funnel-like lateral gland openings on the sides of the notogaster, set Herman apart from any other oribatid mites.

Hermanniellidae > Hermanniella cf.granulata

Although not currently represented here, it's important to note that the Hermanniella genus is in the Hermanniellidae family, which should not be confused with the closely related Hermannia species in the Hermanniidae family.

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Brachypylina > Pycnonoticae > Neoliodoidea > Neoliodidae

There are a number of oribatid species that either carry remnants of their nymphal scalps, or have deliberately adorned themselves with various bits of detritus to help disguise their true appearance, but the various members of this family have taken the art to whole new level. They are heavily sclerotized mites that bear concentric nymphal exuviae - the shed skins of their previous development stages. Adults will have the remains of the larval scalps on top followed, in theory, by the protonymphal, deutonymphal and tritonymphal scalps siting underneath; a bit like the growth rings on a tree, which gives a guide to their relative age. They're certainly different and, once seen, they're not likely to be misidentified unless you find a completely 'clean' individual on its own like the one pictured below.

The Neoliodidae family occurs in many areas of the world with over fifty species recorded that are placed in four genera; Neoliodes, Platyliodes, Poroliodes and Teleioliodes. In Britain we have three species although, as far as I can ascertain, only two are normally considered. The first is Neoliodes theleproctus, regarded as the 'type species' of the family, and the second is Poroliodes farinosus as featured here.

They are closely related to the Hermanniellidae and, from my limited experience, are often found in the company of Hermanniella granulata. Immature individuals are about the same size, certainly under a 1mm, but adults are significantly bigger, probably nearer to 1.5mm and, because of their 'package' are one of the larger oribatids that you could hope to encounter. Neoliodes theleproctus is an arboreal species that appears to favour drier habitats. I'm not sure whether Poroliodes farinosus has the same ecology, but all of the individuals here and that I've subsequently found have been on very dry deadwood or bark on the hillside of a coniferous forest.

Finally, and without wanting to make the classification of these species more complex than it already is, but it's worth mentioning that the family was historically known as Liodidae until it was noted that the type genus Liodes could be confused with the fungus beetle genus Leiodes.

Neoliodidae > Poroliodes farinosus

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Nothrina > Crotonioidea > Camisiidae

Depending on the source of the classification system being referenced, Camisiidae is one of five, or possibly six, families within the Nothrina hyporder (cohort). The primary identification features of these particular families relate to whether the coxae are fused, and details regarding the structure of the genital shields. Obviously, those details can't be determined when attempting to photograph mites in their natural habitat, so it's fortunate that the representative species featured here can be visually distinguished to some degree.

The Camisia genus includes nine species that have a very distinctive oblong-shaped notogaster with central ridges and lateral depressions. They are tiny, slow-moving creatures that often try to camouflage themselves by carrying an encrusted layer of dirt and other bits of organic debris on their back.

Camisidae > Camisia sp.

The second individual is probably Platynothrus peltifer, although I'm a bit wary confirming that for certain as there are four species in the genus that I presume are similar. However, Platynothrus peltifer is generally regarded as the 'type species' as it's found in many areas of the world and has been well-studied as an important decomposer of organic material. Although primarily found in damp forest soils and litter, they have been recorded from many other habitats including wetlands. In addition to the role it plays in recycling nutrients back into the soil it is also a popular food source for various small insects and spiders, especially certain species of ants and beetles.

Platynothrus peltifer is a slightly larger species with mature adults typically averaging a little over a 1mm long. They may also be seen carrying fragments of soil and various bits of debris, which is a characteristic trait of most of the members of the family.

Camisidae > Platynothrus peltifer

The Crotonioidea superfamily also includes the Nothridae family, which includes five species in the Nothrus genus. They are superficially similar to the above and, I believe, of a size that can be found and photographed, so hopefully it's another species that can be added at some point.

ACARIFORMES > Sarcoptiformes > Oribatida

Mixonomata (=Mixonomatides) > Euptyctima > Phthiracaroidea > Phthiracaridae

The final section in this collection includes the 'box mites' that have a ptychoid body form where the ventral plates are adapted, which allows the mite to withdraw its legs and roll or fold-up into a protected ball.

They are classified within the Mixonomata infraorder, which is positioned almost at the bottom of the oribatid taxonomic tree. There are two divisions, Dichosomata and Euptyctima. The former is very small with just four species, even though three families are represented. Euptyctima also includes three families, Euphthiracaridae with four species in three genera, Oribotritiidae with just three species in two genera, and Phthiracaridae as featured here with twenty-one species in four genera.

The largest genus by far is Phthiracarus with 14 recognised species, but regardless of their variable size and colour they can't be specifically identified from photos. In fact, despite their very distinctive appearance you really need to see the ventral shields to eliminate any chance of confusion with similar species from either of the other two families. Fortunately, these mites have a habit of tripping over and ending up on their backs for a while until they can flip themselves back over. It's a shame, but obviously it provides an opportunity of getting a few shots of the underside that would otherwise be very difficult in the field. Another possibility, is if you find one rolled up on its side. You can't be sure, but it's highly likely that, even if it's not the individual you're photographing, it will be the same family. In Phthiracarus, there's a genital shield fused to an adjoining anal shield which are broad and aligned, with the rear edge of the anal shield being rounded. If they're long and narrow, you need to refer to the key to determine the family.

Phthiracaridae > Phithiracarus sp.

Last up we have another very distinctive mite Steganacarus magnus, which can be identified or at least determined 'very likely' if the body setae are of similar size, sticking up on the top, and a bit more 'slicked back' on the sides. Ideally, it would also be good if you can see long hairs on the anal shield, but you need a bit of luck like I had with the individual featured here that had fallen over and, even though it was the wrong way round, they were still visible. There are three other species in the genus though, so if in doubt I just label them as Steganacarus sp.

Phthiracaridae > Steganacarus magnus (confirmed)

I'm not going to read anything into the colour as it probably covers every shade of brown, but I've photographed a lot of these and have noticed that different populations seem to have a consistent colour between the individuals that can almost be defined as tan-brown, reddish-brown or dark chestnut-brown.

The good thing with these mites are that they're relatively common, slow moving and probably the largest oribatid you're going to find as they're typically around 1.5mm, so they give you plenty of opportunities.

Phthiracaridae > Steganacarus sp.

ACARIFORMES > Sarcoptiformes > Oribatida

Desmonomata (=Desmonomatides) > Astigmata (=Astigmatina)

I'm conscious that I didn't mention Astigmata in the main introduction as I can't represent them. In fact, I'm not even sure whether I've seen one. They are closely allied to Oribatida, but are usually treated as a separate group. There are 370 or so species, mainly white to pale-brown in colour, soft-bodied, poorly sclerotised, usually narrower at the front than the back, and often with long hairs. They are mainly associated with animal nests, tree holes or regarded as pest species found indoors (house mites) that can cause damage to furnishings or stored produce. I've also read that unlike regular oribatids, these mites are quick-moving which, together with their tiny size, probably explains why you see very few photos taken in habitat.