Download A Key to Soil Mites in the UK Test version 1: 7 March 2014

A Key to Soil Mites in the UK
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Test version 1: 7 March 2014
Felicity Crotty, and Matthew Shepherd
With thanks to David Harding for figures and some text.
Introduction
Mites (Sub-class Acari) are at first glance similar to spiders (Arachnida). However mites can be distinguished from
spiders by their lack of a waist between the thorax (where the legs are attached) and the abdomen. This gives the
characteristic appearance of a single oval body, with head and legs attached to it. This key should help you to
distinguish the major groups of mites found in UK soil and litter. It aims to enable you to distinguish major groups of
soil mites based on untreated, undissected specimens using a compound microscope with top and bottom lighting.
Mite Ecology
Mites and ticks are a heterogeneous collection of arachnids, including herbivorous, parasitic and saprophagous
(detritus-feeding) species as well as predators. In fact there are almost no lifestyles to which mites have not become
adapted, with some generating and living within plant galls, and some Demodex sp. even living on human foreheads!
This diversity in ecology and behaviour is likely to be the reason for the vast diversity in morphological
characteristics, with different groups adapted in different ways to their surrounding environments. Many species of
mite change their ecological niches at different stages in their life, with parasitic nymphs, phoretic stages that hitch a
lift on other animals, and active hunting adults. The diversity of species of mites within just one ecosystem has
perplexed scientists for many years, with many wondering how so many different species can be living in the same
space
Habitats
Mites can be found in all ecosystems globally, from soil in desert and arctic environments to grasslands and tropical
rainforests. Mites can be found living in arboreal environments, within plant galls, parasitic on other invertebrates
and vertebrates and some mites are even aquatic. This key concentrates on those mites that can be found in soil and
litter habitats, however it should also work for mites inhabiting suspended soils in canopies.
Feeding
Soil mites are generally recognised to be mostly decomposers/microbivores or predators. Feeding mode, will affect
the morphology of mouth parts, typically particulate feeders have large chelate chelicerae (e.g. Oribatid and
Mesostigmatid mites), whilst for suctorial feeders mouthparts are more elongated (e.g. Prostigmatid mites). Most
Mesostigmata are active, well-armoured predators, but some (Uropodidae) are slow-moving fungal feeders.
Oribatids are considered to be decomposers, consuming fungi and bacteria on organic matter
(mycophagy/microbivory), or the organic debris itself (detritivory/saprophagy). Prostigmatid mites have a more
cosmopolitan feeding strategy, being a mixture of predators, fungivores or omnivores, however all known
Prostigmata consume their food by fluid feeding.
Breeding
Mites breed both sexually and asexually (parthenogenetically) depending on species. Sexual reproduction can
involve the transfer of sperm either directly or indirectly. Sperm transfer can be via the chelicera, or via the
aedeagus directly to the female genital opening or even just by leaving a spermatophore (stalked sperm packet) in
the environment to be picked up by a female later.
Growth and Development
Mites go through five instars between egg laying and maturity. These include a prelarva (sometimes prolarva) stage,
larva, protonymph, deutonymph (or deuteronymph also sometimes hypopus depending on species), tritonymph,
before becoming an adult. Before full development as an adult it is common for the mites to have a reduced number
of legs, have a non-feeding stage of development, or use this stage for dispersal by phoresy. It is very difficult to
identify a mite using this key if it is not an adult.
Dispersal
Mites are known to disperse actively (through movement across / within soils) and passively (via rafting, wind
dispersal) as well as by phoresy (hitching a lift on other organisms). Through passive dispersal and phoresy they can
be transported many km’s across habitats. The distance covered by active dispersal is species dependent – oribatid’s
for example have been found to travel 0.3-2.1 cm per day although predatory Mesostigmata have been found to
travel faster than this across habitats.
Predators
During the growth and developmental stages all mites go through to get to adulthood, all mites are initially at risk
from predation, from their own species as well as other mites and the other large predators that reside in the soil
(e.g. pseudoscorpions, centipedes and staphylinid beetles). However, for some species once they reach maturity
they actually suffer from very little predation pressure, usually because they have invested in predator defence
mechanisms like sclerotisation/armour, this is why sometimes it is suggested that Oribatids live in an enemy-free
space.
Trends and threats
There is such a huge diversity of mite species, that to the beginner acarologist could seem quite a daunting task,
however, everything is not everywhere! Some mites are specialists to certain habitats and there is still a large
potential for biodiversity loss through habitat destruction – much like other faunal groups. We unfortunately are also
suffering from a taxonomic impediment, where it is difficult to cultivate expertise in mite taxonomy and when it has
been taught, it is very difficult to retain these experts within scientific and naturalist jobs, threatening our knowledge
of this fascinating group.
A Taxonomic Apology
The taxonomic groups which this key can identify are not at the same taxonomic levels. This is both for practical
reasons – resolving specimens to greater taxonomic detail may require specimens cleared in lactic acid, phase
contrast, oil immersion, require both male and female specimens, or complicated approaches based on the locations
of hairs (setae) or sensory organs. However, it also reflects the seemingly constant changes in mite taxonomy, with
groups that were previously considered at the same level, now appearing at very different places in taxonomic
diagrams. Increasing knowledge of the genetics of mites is gradually resolving taxonomy so that it’s no longer based
on observation of features, which may be misleading, and becoming based on the pattern of evolutionary change, as
evidenced by the clues left in each species genetic material. This should, we hope, enable the taxonomy to become
more settled, longer lasting and valid in evolutionary terms.
The “trunk” of this evolutionary tree is not so very complicated. Mites fit into the tree of life as part of the animal
kingdom, in the ecdysozoa (animals that shed their exoskeletons), among the arthropod phylum (jointed limbs) and
in the chelicerata (animals with pincer-like mouthparts) and the class Arachnida (spiders, scorpions,
pseudoscorpions, ticks and mites).
However, within the sub-class Acari things get more complex. There is a major division between Super-order
Acariformes and Parastiformes, and these are further divided into six orders. Some orders only contain a single
super-family, and so once you’ve identified the order, you’ve already got down to super-family level. However, most
of the soil-dwelling orders have a variety of levels, some with sub-orders within them, these are split (in some cases)
into super-cohorts, then cohorts, some with sub-cohorts, under which lie superfamilies, familes and (finally!) genera
and species. Figures 1 and 2 provide schematics showing how the two superorders are subdivided, indicating which
groups are unlikely to be found in the UK, and showing the taxonomic level to which this key can take you.
These levels are used for general identification of mites for ecological monitoring purposes, and identification to
these groups should help to separate groups playing different roles within the soil and litter ecosystem.
If you’re really bitten by the acarology bug, following the keys in Dindal or “The Manual of Acarology”, may help, but
these may require a more complicated process, access to both male and female specimens, and may require some
dissection and clearing of specimens.
Figure 1: Taxonomy of Acari in the super-order Parasitformes. Grey boxes are groups not normally found in the UK, and the blue box shows those not normally found in
soil. Superfamilies are indicated by bold italic text, and are included under those groups for which there are no further subdivisions. These are named where there is only
one superfamily, or the number of superfamilies given. The most detailed taxonomic levels which this key can identify are identified in red text.
Figure 2: Taxonomy of Acari in the super-order Acariformes, following the system used in figure 1 above.
Mite Anatomy
Where possible, terms in common usage have been used, but it’s worth getting to know some specific terms.
The basic division of the acarine body is into two sections: the gnathosoma (jaw-body or “head”) and the idiosoma
(distinct-body or main body) although depending on group it can be referred to differently (Figure 3). The
gnathosoma bears mouthparts comprising a pair of chelicerae (often pincer like) and paired palps (or pedipalps)
which are leg-like appendages either side of the mouthparts. The idiosoma bears four pairs of legs in the vast
majority of species, although young mites often start with only three pairs, whilst gall mites have only two pairs.
Legs and palps are divided into segments which are named from their tip (distal end - furthest from the body), which
may also bear another structure (claws, hooks, pads or projections) called an apotele, or setae (hairs) which often
act as sensory organs. Counting back from the distal end, the leg segments are:
Tarsus – Tibia – Genu – Femur – Trochanter – Coxa
Where segments have been lost through evolutionary change, the naming runs from the distal end (tip), thus a 4segmented palp has only a tarsus, tibia, genu and femur.
The simple body division into gnathosoma and idiosoma is most easily seen in ticks and Mesostigmata, but can be
subject to fusion and subdivision in other groups. For this reason mites in different groups often have different
names for different parts of the body. In several groups the idiosoma is divided by a furrow called the sejugal furrow
into two sections, which may be evident on the dorsal (back) side or on both dorsal and ventral side. These two
sections are called the opisthosoma (rear body / abdomen) and the propodosoma (front-foot-body) which bears the
first two pairs of legs.
Figure 3: Arbitrary/jargon body divisions in mites.
Many mites breathe through holes in their exoskeleton called stigmata (singular is stigma) which is often associated
with a channel called a peritreme. These peritremes can be located on the sides of the animal (Mesostigmata), or
around the mouthparts (Prostigmata), or may not be visible at all (Oribatida).
The body parts of each of the major groups of acari are illustrated in the following sections.
Ticks – Ixodidae and Argasidae
Ticks are not normally found in soil, being blood-sucking parasites of vertebrates. Although they can be found living
in nests or on vegetation. Superficially similar to mestostigmatid mites they do not feature in this key, but diagrams
provided here should help in case a tick is found by accident.
Besides hard ticks (ixodidae) there are also soft ticks (argasidae) which, in the UK, are parasites of bats, pigeons and
seabirds. Subcapitulum with denticulate hypostome (attachment organ), palps usually with four or fewer segments
and without an apotele. You are unlikely to find these in soil.
Mesostigmata
About one quarter of all mite species identified belong to the Mesostigmata. Mesostigmata are able to move all 6 leg
segments independently, whereas in other orders the coxae are fused or absent. Mesostigmata undersides are a
series of shields which differ between male and females, with flexible tissue between the shields called integument.
Mesostigmata have a pair of lateral stigmatal openings usually around the level of coxae II-IV, often associated with
elongated peritremes. A transverse genital aperture (cat flap) in the intercoxal region of the female covered by 1-4
epigynal shields.
Astigmata
Astigmata (also referred to as Astigmatina, Acaridaiae and Acaridida in some text books) are part of the
Sarcoptiformes, and allied to the Oribatids, and recent phylogenies place them within the Oribatida. They tend to be
white, hairy, range from relatively small to quite large and have only five free leg segments with the coxae fused to
their body and reduced to internal sclerotized channels called apodemes. They can be very common within
disturbed soils, and dust mites are part of this group. Astigmata do not have stigmatal opening or peritremes, and
the gnathosoma is exposed. Perpendicular genital and anal openings (“bomb bay doors”), males aedeagus visible,
females usually with two genital papillae.
apodemes
Oribatida
Oribatids (sometimes referred to as beetle, box or moss mites): most oribatid mites inhabit the soil-litter layer and
are considered to be the main decomposers of litter and organic matter. They have their idiosoma split into at least
two sections when viewed from above (dorsal), comprising a front shield (the “prodorsum” ) covering the front of
the body (proterosoma) often extending far forward covering the “head”. The rear “notogaster” (back-stomach),
covering the hysterosome (rear of body). The prodorsum often supports two trichobothria, which are feather-like or
other-shaped projections set in pits in the shield called bothridia (sing. bothridium).
The true gnathosoma of these mites is often hidden under the projecting front part of the proterosome called a
camerostome (“chamber-hole”). In most oribatids, the mouthparts can be seen to support two club-like organs
called rutella (sing. rutellum) when viewed from the underside. The presence or absence of these, and the line
where these join the underside of the head can be an important features depending on whether they form a straight
line (diarthric) typical of most brachypyline mites, an angled line (stenarthric like a Ʌ), or are not jointed at all
(anarthric). The chelicerae are often hard to see, tucked deep within the camerostome and are usually twosegmented and commonly chelate-dentate (although occasionally pelopsiform (elongated / suctorial)).
The underside of Oribatids bear genital and anal plates, which in this group characteristically are arranged to enable
them to open up along a vertical suture, rather like the bomb-bay doors of an aircraft.
Prostigmata
These mites are very variable in their form, and have the largest size range across all the mite groups (from very
small <0.1mm to very large >1cm). They are mainly soft-bodied, with the idiosoma often wider towards the front
than at the back. They can have eyes, which are rare among other groups, and may have strongly modified palps
and chelicerae. They can either be brightly coloured (especially in larger species such as velvet mites) or very tiny
and more or less transparent. Their genital and anal openings are not typically sclerotized and often only a suture
line is visible (although still opening vertically like bomb-bay doors). They often have highly modified legs, which can
finish in brooms of long seta, or large claws. The stigmatal opening is often difficult to see under a dissecting scope,
however it is located near the chelicerae or at the top margin of the idiosoma.
Collecting, handling and examining soil mites
Soil mites can be collected for casual observation or recording simply by searching through litter or soil and
collecting moving mites with a pooter. When you appreciate the scale of soil mites, however, the size of the meshes
often provided on standard entomologists’ pooters can seem alarmingly large, and it probably worth adapting a
small pooter with as fine a mesh as you can find. Placing litter or soil into a white plastic tray makes it easier to
locate mites, by moving the litter to one side and watching for mites moving against the tray’s base. Placing litter or
soil into a coarse mesh (>2mm) and gently agitating it over the plastic tray to let the mites fall into the tray along
with smaller debris, can also be effective. It is worth noting that the faster moving predatory mites are relatively
easy to spot using this technique, but slower moving microbivores may be harder to spot (particularly the box mites,
which close up when disturbed). The hardest part is adapting your search technique to see the mites which are much
smaller than other invertebrates obtained with a pooter – but once you have adapted to this scale, you will see them
everywhere! Sweep nets can also be used to collect mites from vegetation.
A more thorough and rigorous method for collecting mites is to extract the mites and other mesofauna from a litter
sample or soil core using a Tullgren funnel. Litter or very fine flakey soil may benefit from being placed on top of a
layer of wide-mesh cloth (e.g. muslin or cheesecloth) to prevent too many mite-sized particles from falling through
the Tullgren funnel.
Soil cores can be collected in any manner, but if you’re interested in using your data to describe the numbers or
density of animals it’s best to collect a soil core of known volume. Because most soil mesofauna inhabits the topsoil,
monitoring work such as that carried out for the Countryside Survey, or by Natural England, collects soil cores from 0
– 10cm deep, by driving lengths of plumber’s waste pipe into the soil and then digging it out, intact, with a trowel.
Taping a gauze over the top of these pipes before driving them into the soil will stop the larger more active surface
fauna from escaping once the core has been driven in. Once extracted from the soil, you should wrap up the core in
clingfilm, or place within an individual plastic sample bag and keep it cool (a fridge at 4oC is ideal) until you’re ready
to extract the soil animals.
Tullgren funnels can be easily set up by amateurs using kitchen supplies and household goods, but if you’re doing a
lot of work on mites, you’ll probably need to build something more elaborate. A Tullgren funnel is a funnel lined
with a 2mm mesh suspended over a container of liquid, and held under a 40 watt incandescent light bulb (energy
saving bulbs don’t emit enough heat!). This set up can also be created by using fairy lights placed directly within top
of drainpipe, over mesh (Figure). Your litter or soil core is placed in the funnel and the soil organisms will be driven
out of the sample by the light, heat and dryness, go through the mesh and fall into the liquid trap at the bottom.
When using soil cores carefully remove any mesh from the core, and place it upside down in the funnel, with the
original soil surface facing downwards. This is because larger organisms tend to inhabit the upper layers of soil, and
may not be able to travel through the smaller pores found lower down in the soil. It normally takes 5 days to
complete the extraction (however a lot depends on the size and wetness of the soil core), with a slow drying helping
the animals to move through the soil, rather than drying them out in situ.
The liquid can be water, if you’re interested in keeping your specimens alive (however you should aim to change
collecting vial daily to prevent losses through predation). Springtails often float on the surface, while mites sink to
the bottom. More commonly, you can use alcohol to kill and preserve your specimens until you’re ready to examine
them. You can buy 70% industrial methylated spirits (without the purple dye) from suppliers of cleaning products,
which is fine for preserving specimens, but if you’re interested in submitting your samples for genetic analysis then
stronger alcohol is recommended. Of course, if you’re using alcohol you should keep it in a safe place, away from
children and set up your extraction in a well ventilated area, child-free and away from sources of ignition.
Preserving and recording
You should aim to record details of your collection, even if you can’t identify the animals to species level, as is the
case with this key. A good way to do this is to keep your specimens in at least 70% alcohol in a small glass or plastic
vial, sealed with a bung, and include a slip of paper with key details of the specimen. You should use pencil (biro will
dissolve in alcohol) and write your name, the date the sample was collected, the location (postcode is good, grid
reference is better), habitat and what you think the specimen is. Because mites are usually very small, the
immediate location can be described according to micro-habitat.
Unfortunately most biological recording systems (such as www.irecord.org) will only allow you to record data at the
level of species, or sometimes genus. This is a tall order for an amateur acarologist! This does not mean that your
records are not useful, however. Much scientific research has been conducted usefully using taxonomic levels that
are similar to, or at lower resolution, than the levels provided in this key.
The Key
This key is dichotomous, which means it relies on following one of two choices, based on a description of features.
Choose the description that fits your specimen best, and if this seems to lead to the wrong answer, retrace your
steps using the numbers in brackets, and explore whether you’ve gone down the correct route.
The 4 major groups of mites in soil have their backgrounds colour coded with orange for Mesostigmata, pale blue for
Astigmata, pale brown for Oribatida and pink for Prostigmata. Parts of the key leading to one or more of these
groups are in white.
Photographs of features as they appear under a light microscope, with bottom or top lighting, illustrate the features
described. Please note that the features on your specimen may not always look exactly like the pictures here. Mites
are very variable creatures.
1.
2.(1)
3.(2)
Three pairs of legs (do not confuse
palps with legs!)
Four pairs of legs
Six free leg segments (ie. coxae not
fused into ventral shield or absent);
palps with apotele on last segment.
Stigmata and lateral peritremes always
visible. Either disc-shaped animals or
predatory mites “spider-like”, no
trichobothria.
Mite larva1
Five free leg segments (not counting
claw, coxae fused to body) OR leg
segments are inside a shell-like
arrangement of shields and cannot
easily be counted.
Rear leg (leg IV) with small plate
inserted near the base of the underside
of the tarsus (segment nearest foot)
bearing 2 bristles (setae). Epigynal
shield either with 6 setae (rarely 2-4)
Sejida; or a complex of 2-4 genital
shields Trigynaspida.
11
Rear leg has no such small plate at the
base of the tarsus. One epigynal shield
with only 0-1 pairs of setae.
1
2
Order:
Mesostigmata 3
Small plate
(intercalary
sclerite)
Order:
Mesostigmata
Sub-orders:
Trigynaspida or
Sejida 10
Order:
Mesostigmata
Sub-order:
Monogynaspida 4
You may still be able to key out a major group for this specimen – go to question 2 but be careful that some features may not
match exactly. The exoskeletons of six-legged larvae may not be as well-armoured, for example.
4.(3)
Roundish disc shaped animal (flying
saucer like), each leg can be withdrawn
into a hollow beside it (pedofossae).
Beware that some oribatids can do this
– count leg segments carefully and look
for peritremes and stigmata!
Order:
Mesostigmata
Cohort Uropodina,
Sub-cohort
Uropodiae
pedofossa
Stigmata
5.(4)
6(5)
7.(6)
Not matching this description
Animals with a pair of disc-shaped
suckers either side of the anus, roughly
circular and flattened. Parasites of
myriopods. (rare)
Not matching this description
5
Order:
Mesostigmata
Cohort
Heterozerconina
6
Dorsum covered by more than two
shields, including a pygidial shield/plate
(back rear end) with setae
Order:
Mesostigmata
Cohort
Microgynoidea
Order:
Mesostigmata
Cohort Gamasina 7
Order:
Mesostigmata
Sub-cohort
Epicriiae,
Dorsum (usually) covered by single
shield no free mesonotal or pygidial
plates with setae
Dorsal side of body covered in patterns
of numerous 3-4 lobed warts, sides
with paired tubercles and long hairs –
peritremes not visible. Tarsi with
clubbed setae and paired claws.
8.(7)
Body without patterns of warty lumps,
tubercles. Predatory mites usually with
peritremes visible along the lateral sides
of the body behind the legs when
viewing venter. Stigmata visible
between legs III and IV. With or without
paired claws.
Dorsal shield resembles a police badge.
In female – genital shield comes to a
triangular point at its front edge. Male
has spurs on leg IV only.
In male there is a groove-like
spermatotreme on the movable digit of
the chelicerae.
8
Female genital shield squarer or axeshaped. Male has either unmodified
chelicerae or long spermatodactyl, and
may have spurs on leg II.
9
Adult females with a truncated dorsal
shield not covering all of opisthonotal
region (Males all covered). Pygidial
sclerite resembling infinity (∞) (without
Order:
Mesostigmata
Sub-cohort:
Arctacariae,
Order:
Mesostigmata
Sub-cohort:
Parasitiae
9.(8)
setae). Chelicerae enlarged. Peritremes
extending to level of legs I or II only.
(Very rare in UK)
Animal not matching this description.
Peritremes may be long (over many
coxae) or short. Male: moveable digit
of chelicerae with spermatodactyl, male
genital opening at the front edge of
ventral shield, males may have spurs or
tubercles on legs II and or IV. Sternal
shield entire with 2-4 pairs of setae.
May lack claws on tarsus I. (Most
common group).
10.(3)
11.(2)
12.(11)
Females have a truncated diamond
shaped genital plates made up of a
small, rear central shield and two larger
lateral shields (Tri = three and gynaspid
= genital shield), although can be 2-4
shields. Males have genital opening at
the front edge of a plate. Chelicerae
may have mop- or brush-like
excrescences at their bases.
Female genital plate is a simple flap,
males genital plate is a sub-circular
valve set into the plate between the
coxae (leg bases). Chelicerae without
excresences, body often with tubercles
or horn-like protrusions. Epigynal shield
with 6 (or more) setae (occasionally
only 2-4).
Animals with only vestigial head and
mouthparts present between front legs
(Deuteronymph stage), and sucker-discs
at the rear ventral side
Animals with fully formed mouth parts
and no sucker plates
Often tiny animals, adult females with
stigmatal opening either side of
gnathosoma (near palps). End of leg IV
not developed in females, hind legs
either modified into long brush/broomlike structures, reduced to thin prongs,
long whip-like hairs or single massive
Superfamily
Arctacaroidea
Order:
Mesostigmata
Sub-cohort:
Dermanyssiae
Superfamilies
within sub-cohort:
1) Veigaioidea
2) Rhodacaroidea
3) Eviphidoidea
4) Ascoidea
5) Phytoseioidea
6) Dermanyssoidea
Order:
Mesostigmata
Sub-order:
Trigynaspida
Order:
Mesostigmata
Sub-order: Sejida
Order:
Sarcoptiformes;
Sub-order:
Oribatida;
Cohort: Astigmata,
Hypopi (phoretic
life stage)
12
Order:
Trombidiformes;
Sub-order:
Prostigmata;
Super-Cohort:
Eleutherengonides;
Cohort:
13.(12)
claws. Palps usually reduced to 2-3
segments.
Heterostigmata
Animal may be strongly or weakly
sclerotised, but hind legs with claws or
pads, all legs fully developed - never
with brush/broom- or whip-like
structures. Stigmatal openings at base
or on gnathosoma, or not visible at all.
Palps variable but usually 3-5 segments.
Teardrop-shaped animals, leg coxae
fused into ventral plate with
apodemes, body normally white, often
with long hairs, trichobothria always
absent, with single claws or no claws.
Females with v-shaped genital plates,
male with aedegus and anal suckers.
13
Sejugal furrow
Simple setae
– no
trichobothria
Order:
Sarcoptiformes;
Sub-order:
Oribatida;
Cohort: Astigmata
V-shaped genital
plates
Male anal
region
14.(13)
Animals not fitting this description,
may/may not have trichobothria, may /
may not have sejugal furrow, zero,
single or multiple claws. Males do not
have anal region as above.
Animals with genital and anal plates
open longitudinally like bomb-bay doors
on aircraft. Commonly strongly
sclerotised and redish, brownish or
blackish, at least on legs. Body shape
narrower at front than back (tear-drop).
Mouthparts may have rutella, and
14
Order:
Sarcoptiformes;
Sub-order:
Oribatida 15
chelicerae typically chelate (rarely
modified) and palps are simple (never
with thumbclaw, although not always
easy to see). Often with dark-spots (oil
glands) on both the rear flanks. Legs I-IV
with 1 or 3 claws (rarely bidactyl),
empodium claw or sucker-like never
pad-like. Stigmata and peritremes
NEVER present or visible.
15.(14)
Genital and anal openings without
plates. Often weakly sclerotised (beanbag-like), although some forms strongly
sclerotized (labidostommatides), body
often wider at front than at back, colour
can be white, yellow, green, red.
Mouthparts without rutella. Palps and
chelicerae often modified (rarely
chelate) always fairly visible. At least
legs II and III with 2 lateral claws,
empodium may be pad-like, often with
tenant hairs. Lacking oil glands.
Stigmata opening between cheliceral
bases on gnathosoma.
Order:
Trombidiformes;
Sub-order:
Prostigmata 22
Animals ptychoid – prosoma and
opisthosoma hinged (dorsal shields split
into front and back that can fold up to
enclose the animal – a bit
armadillo/hedgehog-like).
16
16.(15)
17. (15)
Animals not capable of folding up like
this
Body sclerotisation strong. Mouthparts
with rutella broad (massive). Rear sides
of body (opisthosome) may have oil
glands Hyseterosoma not segmented.
Genital and anal openings touching
each other (resembles a sash window
with four panes). Pretarsi often
monodactyl or tridactyl
Mouthparts lacking rutella/rutella
narrow. Body sclerotisation strong.
Opisthosomal glands absent.
Hysterosoma sometimes segmented.
Pretarsi various although usually
monodactyl.
Animals with obvious “knees” – genu is
shorter than other leg segments
(particularly tibia) and leg usually bends
more here. Legs often within a deep
pockets in body – like a ball and socket
joint (acetabula). Genital and anal
plates are set apart from each other,
with no adjacent small adanal or
adgenital shields, and are entirely
enclosed in a single fused ventral shield,
which continues to the mouthparts.
Subcapitulum usually diarthric (no
ventral sejugal furrow). [most common
super-cohort].
17
Sub-order:
Oribatida
Super-cohort:
Mixonomata,
Infra-orders:
Euptyctima and
Dichosomata.
(Common name –
box mites)
Sub-order:
Oribatida
Super-cohort:
Enarthronota
Sub-order:
Oribatida
Super-cohort:
Brachypylina –
Higher oribatids
(Euoribatida)
Infra-orders:
Pycnonoticae and
Poronoticae.
Small
“knees”
Genital and anal
plates set apart in
single shield
Animals with most leg segments a
similar size - genu not noticeably
different from other leg segments.
Genital and anal plates can be adjacent
to each other, or not completely
surrounded by ventral shield, or with
adgenital or adanal plates. Ventral
shield may be separated from coxal
plates, and sejugal furrow may be
present.
Genu ~same as
tibia not knee
like
Genital and anal plates
may be adjacent
18.(17)
Sub-order:
Oribatida
Macropyline –
Super-cohorts:
Parhyposomata,
Palaeosomata,
Desmonomata.
Lower Oribatids 18
Adanal and adgenital
plates present
Weakly sclerotised bodies, often with
long black hairs. Mouthparts always
visible from above (astegasime) without
rostral tectum. Femur (fourth from end
of leg) divided – so appears to have 6
free leg segments (do not confuse with
Mesostigmata). Never with oil glands
on the sides of the opisthosoma, and
legs never ending with single claw (2 or
3 claws).
Sub-order:
Oribatida
Super-cohort:
Palaeosomata
Femur divided
here
2 or 3 (as here) claws
Femurs not divided, legs with only 5
free segments. Mouthparts can be
hidden under projecting dorsal shield.
Bodies usually light/dark brown with
noticeable sclerotisation (rarely
19
19.(18)
unsclerotised to some extent).
Opisthosomal oil glands may be
present, single claws may be present.
Normal hairs on notogaster.
Holoid body type - always lacking
flexible cuticle between leg pairs II and
III (though a furrow may be present).
Adults always strongly sclerotised
(though nymphs can be weakly
sclerotised, wrinkly, with unsclerotised
anal plates and single claws). Usually
with distinct adgenital and/or adanal
plates, always with opisthosomal oil
glands, mouthparts always concealed
under projecting front dorsal shield
(stegasime).
Sub-order:
Oribatida
Super-cohort:
Desmonomata
Dichoid body type - with flexible cuticle
between legs 2 and 3, strongly or
weakly sclerotised animals with or
without oil glands, mouthparts
concealed or visible from above.
20
Flexible cuticle
20.(19)
21.(20)
Rutella either diarthic (connected to
underside of head with joints in a
relatively straight line) or fixed (not
jointed). Oil glands absent. Usually only
one claw on pretarsi. Notogastral
scissures present (1-3).
Rutella stenarthric (joined to underside
of head with angled joints). Oil glands
may be present. Notogastral scissures
either not present or only 1 present.
Notogaster entire with no scissures
(cracks), never divided into 3 sections.
Mouthparts normally hidden under
projecting front dorsal shield. Oil glands
may be absent (secondarily lost) or
present. Brown, reddish, beige or
yellow.
Sub-order:
Oribatida
Super-cohort:
Enarthronota (non
– ptychoid)
May have 1 scissure in notogaster,
however notogaster often split into 3
Sub-order:
Oribatida
21
Sub-order:
Oribatida
Super-cohort:
Mixonomata (non
ptychoid)
22.(14)
sections – Trichoid body type
(opistonotum divided after leg IV), with
lateral, usually protruding oil glands.
Mouthparts sometimes visible from
above. White or tan coloured, weakly
sclerotised. Legs ending in 1, 2 or 3
claws.
Palps with fewer than 5 segments, no
thumb claws on palp tibia.
Palps with 5 segments, palp tibia with
thumb claws.
23.(22)
24 (23)
Super-cohort:
Parhyposomata
23
25
24
Palps with 4 segments, large/obvious.
Stigmatal opening at base of
gnathosoma (no peritreme), on
gnathosoma (with peritreme) or absent.
Cheliceral bases not fused together.
Relatively large mite >1mm.
Palps with 3 or fewer segments – may
be hard to see, although legs usually
have a well-developed terminal claw
and pad-like empodium. In females
stigmata on either side of gnathosoma
(near palps / shoulders of mite) no
peritremes. Males often have genital
suckers for copulation. White yellow or
brown colouring. Never more than 1
pair of trichobothria present (on
females only), and always capitate, like
a blob on a short stalk). Usually smaller
animals (<1mm), often have a parasitic
or phoretic (travelling on insects) stage.
Palps with 4 segments, with unusual
fusion of genu and tibia, lacks
thumbclaw. Coxae on venter
expanded/plate like (Arnold
Schwarzenegger mite – looks like a 6pack!). Dorsum and venter with alveolar
ornamentation (to varying extents
dependent on species). Stigmata opens
at base of chelicerae. Femora of legs
subdivided (up to 3 times). Heavily
sclerotized.
Sub-order:
Prostigmata;
Super-Cohort:
Eleutherengonides;
Cohort:
Heterostigmata
Sub-order:
Prostigmata;
Super-cohort:
Labidostommatides
25
26.(25)
Palps with 4 segments (rarely 1-5),
sometimes borne on the sides of an
extended snout. May have up to 2 pairs
of trichobothria (various shapes), eyes
and naso usually present. Can be large
and brightly coloured animals (white,
pink, yellow, green, red), although still
weakly sclerotised. Leg I can be long
and antenna-like, and femur IV is often
swollen.
Sub-order:
Prostigmata;
Super-cohort
Eupodina (incl.
superfamily
Bdelloidea - snout
mites)
Trichobothria absent, leg tarsi with
tenent (flattened tip – resembles head
of a nail) hairs. Normally with modified
chelicerae (as whips, blades, stylets),
naso always absent, eyes usually
present. Genital papillae absent in all
stages of development. Adults are small
to medium in size. Males with an
aedagous.
Trichobothria present (1 or 2 pairs).
Genital papillae present normally 2-3
(but can be 0-3 pairs or reduced in
size). Tenent hairs absent.
Peritremes usually absent, however if
present, located between cheliceral
bases. Eye lenses well developed. Often
hypertrichous (hairy) in terrestrial
species. Have 1-2 pairs of trichobothria.
Often medium to large animals, red or
orange in colour, many with velvet-like
coating.
Sub-order:
Prostigmata;
Super-Cohort:
Eleutherengonides;
Cohort
Raphignathae
Peritremes well developed often as
grooves across prodorsum at the base
of the mouthparts, linear, or may
emerge to form prongs with channels.
Chelicerae often sickle-like, bases
separate. Animals may be smaller, often
purple, red, pink or brown. Not
normally velvety. Usually with naso and
well-defined thumb-claw. Not
hypotrichous.
26
Sub-order:
Prostigmata;
Super-Cohort:
Anystides;
Cohort
Parasitengona
(Velvet Mites)
(Large and diverse
clade, with four
sub-cohorts. Larvae
typically parasitic)
Sub-order:
Prostigmata;
Super-Cohort:
Anystides;
Cohort: Anystina