Tridactylidae
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The Tridactylidae are a
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
in the insect order
Orthoptera Orthoptera () is an order of insects that comprises the grasshoppers, locusts, and crickets, including closely related insects, such as the bush crickets or katydids and wētā. The order is subdivided into two suborders: Caelifera – gras ...
. They are small, mole-cricket-like insects, almost always less than long when mature. Generally they are shiny, dark or black, sometimes variegated or sandy-coloured. They commonly live in short tunnels and are commonly known as pygmy mole crickets, though they are not closely related to the true "
mole cricket Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole" * Golden mole, southern African mammals * Marsupial mole, Australian mammals Other common meanings * Nevus, a growth on human skin ** Melanocytic nevus, a specific type of ...
s" (
Ensifera Ensifera is a Order (biology), suborder of insects that includes the various types of crickets and their allies, including cricket (insect), true crickets, Rhaphidophoridae, camel crickets, Tettigoniidae, bush crickets or katydids, Prophalangops ...
), as they are included in the
Caelifera The Caelifera are a suborder of orthopteran insects. They include the grasshoppers and grasshopper-like insects, as well as other superfamilies classified with them: the ground-hoppers ( Tetrigoidea) and pygmy mole crickets ( Tridactyloidea). ...
suborder (related to
grasshopper Grasshoppers are a group of insects belonging to the suborder Caelifera. They are amongst what are possibly the most ancient living groups of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grassh ...
s).


Description

The Tridactylidae are small members of the Orthoptera, most species being less than 10 mm in length, though some approach 20 mm. They have a wide, but patchy, distribution on all continents but
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
. Being so small and inconspicuously coloured, while living in shallow burrows in moist sandy soil, they are not generally familiar to non-entomologists. They have several unusual features, for example, the posterior
femora The femur (; : femurs or femora ), or thigh bone is the only bone in the thigh — the region of the lower limb between the hip and the knee. In many four-legged animals the femur is the upper bone of the hindleg. The top of the femur fits in ...
are greatly enlarged, being strongly adapted for leaping; in some species those hind femora actually are larger than the abdomen. Correspondingly, in support of their powerful jumping capabilities, the hind tibiae bear movable plates towards their
distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...
ends. These vary in number according to the genus, and they are called natatory lamellae (meaning literally "swimming plates"). Ordinarily the insect keeps the plates closely pressed against its tibiae but it can fan them out for swimming, which most species can do very well, some even being able to dive and swim under water. Apart from scrabbling over the water or swimming, some species actually can jump off the water surface. It is probable that the natatory lamellae are what makes such implausible leaps possible. The plates also may aid jumping on land, which Tridactylidae certainly can do impressively. The posterior tibiae also bear articulated spines near their tips, plus spurs longer than the hind tarsi, which may be entirely absent or else are at best
vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
, having only a single segment. The insect uses its hind tibial spurs for digging, which is unusual for an insect's hind leg. The
anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
four tarsi, in contrast to the posterior two tarsi, generally have two segments each.Comstock, J. H. An Introduction to Entomology, Comstock Publishing. 1949 The tegmina are reduced in size, rather as in the
Tetrigidae Tetrigidae is an ancient family in the order Orthoptera, which also includes similar families such as crickets, grasshoppers, and their allies. Species within the Tetrigidae are variously called groundhoppers, pygmy grasshoppers,Borror DJ, Tripp ...
, but there is no corresponding extension of the
pronotum The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...
. The vestigial tegmina are horny, almost without veins, and without stridulating organs. In keeping with the lack of stridulatory adaptations, the fore tibiae do not bear
tympanal organ A tympanal organ (or tympanic organ) is a hearing organ in insects, consisting of a tympanal membrane ( tympanum) stretched across a frame backed by an air sac and associated sensory neurons. Sounds vibrate the membrane, and the vibrations are s ...
s such as those found in many
Orthoptera Orthoptera () is an order of insects that comprises the grasshoppers, locusts, and crickets, including closely related insects, such as the bush crickets or katydids and wētā. The order is subdivided into two suborders: Caelifera – gras ...
. Rear wings generally are present, often longer than the abdomen, but their presence in any particular species need not imply that the insect is capable of flight. Tridactylidae give the impression of having two pairs of cerci; this is because, in addition to the true cerci, the two podical plates (comprising the divided sternum of the eleventh abdominal segment) are greatly elongated and each bears a terminal segment that looks like a stylus or
cercus Cerci (: cercus) are paired appendages usually on the rear-most segments of many arthropods, including insects and symphylans. Many forms of cerci serve as sensory organs, but some serve as pinching weapons or as organs of copulation. In many in ...
. The antennae are fairly short, typically
filiform Filiform, thread or filament like, can refer to: * Filiform, a common term used in botany to describe a thread-like shape *Filiform, or filiform catheter, a medical device whose component parts or segments are all cylindrical and more or less un ...
or moniliform, with eleven segments. Some species have vestigial ovipositors, whereas others have ovipositors similar to those of the
Acrididae Acrididae are the predominant family of grasshoppers, comprising some 10,000 of the 11,000 species of the entire suborder Caelifera. The Acrididae are best known because all locusts (swarming grasshoppers) are of the Acrididae. The subfamily Oedi ...
, suited to depositing the eggs in sandy soil.


Taxonomy

Historically Tridactylidae affinities have been the occasion for confusion. Originally they were seen as a subfamily, Tridactylinae, of the
Gryllidae The family Gryllidae contains the subfamilies and genera which entomologists now term true crickets. Having long, whip-like antennae, they belong to the Orthopteran suborder Ensifera, which has been greatly reduced in the last 100 years (''e.g ...
, the true crickets, closely related to the Gryllotalpidae or Gryllotalpinae, but their placement has long been accepted as a parallel or
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
with the 'true' mole crickets. Detailed study of genitalia however, subsequently led to the suggestion that they were nearer to the
Acrididae Acrididae are the predominant family of grasshoppers, comprising some 10,000 of the 11,000 species of the entire suborder Caelifera. The Acrididae are best known because all locusts (swarming grasshoppers) are of the Acrididae. The subfamily Oedi ...
, the grasshoppers. They eventually were assigned to their own family, Tridactylidae which, together with the Cylindrachetidae, form the superfamily Tridactyloidea (Rentz 1996). The family Tridactylidae in turn were split into two families, the Tridactylidae and the Ripipterygidae, or "mud crickets" (Günther 1994; Flook et al. 1999). , ''Orthoptera Species File'' lists two extant (living) subfamilies and one extinct.


Dentridactylinae

Auth. Günther, 1979 # '' Bruntridactylus'' Günther, 1979 # '' Dentridactylus'' Günther, 1974 # '' Paratridactylus'' Ebner, 1943 * †'' Burmadactylus'' Heads, 2009
Burmese amber Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 100 million years ago, during the latest Albian to earliest Cenomanian ages of the mid-Cretaceous period. Th ...
, Myanmar,
Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...
* †'' Cascogryllus'' Poinar, 2018 Burmese amber, Myanmar, Cenomanian * †'' Guntheridactylus'' Azar & Nel, 2008
Oise amber Oise amber () is a type of amber found near the Oise river near Creil in northern France. Oise amber is around 53 million years old, dating to the Early Eocene (Ypresian). Oise amber is softer than Baltic amber, although Oise amber is older ...
, France,
Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...
* †'' Magnidactylus'' Xu et al. 2020 Burmese amber, Myanmar, Cenomanian


Tridactylinae

Auth. Brullé, 1835 * '' Afrotridactylus'' Günther, 1994 * '' Asiotridactylus'' Günther, 1995 - Africa to central Asia * '' Ellipes'' Scudder, 1902 -
Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...
* '' Neotridactylus'' Günther, 1972 - Americas * '' Tridactylus'' Olivier, 1789 * '' Xya'' Latreille, 1809 * †'' Archaeoellipes'' Heads, 2010
Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree '' Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil in ...
,
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
* †'' Cratodactylus'' Martins-Neto, 1990
Crato Formation The Crato Formation is a geologic formation (stratigraphy), formation of Early Cretaceous (Aptian) age in northeastern Brazil's Araripe Basin. It is an important Lagerstätten, Lagerstätte (undisturbed fossil accumulation) for palaeontology, pa ...
, Brazil,
Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...


Extinct genera

* subfamily †Mongoloxyinae Gorochov, 1992 ** †'' Baisoxya'' Gorochov & Maehr, 2008
Zaza Formation The Zaza Formation is a geological formation located in Buryatia (Russia). It dates to the Lower Cretaceous. The age of the formation is disputed, and is considered likely to be Valanginian-Hauterivian, or Aptian in age. It comprises sandstones, ...
, Russia, Aptian ** †'' Birmitoxya'' Gorochov, 2010 Burmese amber, Myanmar, Cenomanian ** †'' Cretoxya'' Gorochov, Jarzembowski & Coram, 2006
Lulworth Formation The Lulworth Formation is a geologic formation in England. It dates from the late Tithonian to the mid Berriasian. It is a subunit of the Purbeck Group. In Dorset, it consists of three members, which are in ascending order, the Mupe Member, the ...
, United Kingdom,
Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 143.1 ±0.6 Ma and 137.05 ± 0.2 (million years ago) ...
** †'' Mongoloxya'' Gorochov, 1992 Dzun-Bain Formation, Mongolia, Aptian ** †'' Monodactyloides'' Sharov, 1968 Zaza Formation, Russia, Aptian * ''
incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
'' ** †'' Paraxya'' Cao, Chen & Yin, 2019 Burmese amber, Myanmar, Cenomanian ** †'' Magnidactylus'' Xu, Fang & Jarzembowski, 2020 Burmese amber, Myanmar, Cenomanian


Biology

The typical habitat of Tridactylidae is moist, sandy soil near water, such as dams, lakes, streams, and sometimes the sea. In such places they dig small tunnels, in which they live, sometimes together with other inoffensive neighbours such as sundry beetles.George W. Folkerts. Egg guarding and its significance in the heterocerid beetle,Dampfius collaris (Kies.) Journal of Insect Behavior Volume 2, Number 1, 139-141, They seem to feed largely on organic detritus, plant material, and in particular, algae, including microscopic algae coating sand grains; they accordingly emerge mainly to feed on moist soil in the light, which permits the growth of the algae on which they depend for food. In some species breeding takes place in their tunnels, eggs being laid in batches of a few dozen. Other species with well-developed ovipositors lay eggs singly in moist soil, but at least some of those species have since been assigned to the family Ripipterygidae, also within the superfamily Tridactyloidea. There is not much available information on such details of their biology.


References

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