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Diplura


  Diplura

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Diplura


  Diplura

 

Diplura
 

Diplurans, sometimes known as the two-pronged bristletails, are seldom seen and when they are, are often mistaken for symphylans or millipedes. But for me, they're far more interesting. And much harder to find.
They are eyeless, whitish, and, like Collembola and Protura, are entognathous, sharing most of the characteristics of the other two's retractable mouthparts, held inside a pouch. This is the main difference that taxonomists held up to initially separate the Entognatha from Insecta, with their grossly inferior and not cool at all external mouthparts. And the lack of wings.

As mentioned on other pages, each of the three members of the still kind of valid but probably polyphyletic class of Entognatha are very unusual. Each has characteristics peculiar to itself, while sharing some others. Diplurans like the Campodeoidea are able to completely regenerate their bead-like antennae, legs and cerci, the long tail appendages, over a series of moults. This unique ability amongst the hexapods hints a little of their ancient pancrustacean ancestors. Modern crustaceans like lobsters are experts, able to start regenerating limbs within days, with moulting aiding the process.

Diplura keep growing and moulting throughout their short, usually one year lives, although it's possible that some species can live around three years, like Collembola. Both diplurans and collembolans look like miniature adults as a newly hatched instar. However, unlike the first instars of Collembola, diplurans spend their first few days immobile, as a pre-larva, similar to pre-larval mites, moulting before beginning to eat and explore their surroundings.

Collembola can also regenerate their antennae to some extent, but it's an incomplete process. This even partial ability is only possible due to the moulting that continues throughout adulthood.
Some insects like the order Blattodea, the cockroaches, are able to regenerate an entire limb in a single moult but only as moulting instars.
All insects, including cockroaches, stop moulting on reaching adulthood, with the exception of Archaeognatha and Zygentoma. These are commonly known as the jumping bristletails, silverfish and firebrats, more unusual ancient hexapods that used to be in a subclass known as Thysanura, together with the three Entognatha. This was before more recent research split them up again, although for some reason, the decision was made to continue calling them insects. One day they'll achieve their own class...

But back to diplurans.

 

Dipluran from Binna Burra, Lamington National Park, Queensland, Australia.

          Fast moving dipluran Somerset, Dec 2013

 

They are incredibly fast. Above you can see a Campodeidae at full pelt, giving some idea why most photos of diplurans are taken from above, rather than the side, as in this one. According to Colin Little in The Colonisation of Land, they can run up to 54mm/s, which works out as twenty seven body lengths per second, or 27 bl/s. A cheetah, in comparison, only travels at 16 bl/s, around 110km/h. For the cheetah to travel at the same relative speed as the mite, it would have to be travelling at 186 km/h.

Both Campodeiodea and Projapygoidea are typically generalist feeders, although with a few rare predatory species in the mix. Even so, many species seem to be largely herbivorous, or detritivores. In comparison, the entirety of Japygoidea are predatory hunters, although still capable of detritivore behaviour.

Diplurans have abdominal appendages on many of their segments, called styli. Archaeognatha and some genera of Zygentoma also have abdominal styli which they use as extra legs in certain situations. it's been presumed that they are functionless in diplurans. This isn't correct, at least with the Campodeidae.
Usually, when traversing a flat surface, the dipluran's body is held out horizontally. But when climbing over uneven surfaces, the styli come into play, walking the abdomen over the surface. To the best of my knowledge, the photo below is the first documented evidence of this behaviour. 

 

         Side view of dipluran, showing abdominal styli in action Wetherby, W. Yorkshire UK Dec 2014

          Close-up of styli on Meinertellidae family of Archaeognatha/Bristletail- Tairua, New Zealand Feb 2016

          Close-up of styli on Australiatelura tasmanica, Zygentoma/silverfish NW Tasmania Jan 2016

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Diplura


Diplura


Happy dipluran Superfamilies
 

Diplurans are usually considered to have three lineages- Campodeoidea, Japygoidea and Projapygoidea. The different superfamilies are defined by the three different types of cerci found across all the dipluran families. 

The Campodeoidea have two long, thread-like cerci on their final abdominal somite, elongated even further in some cave species like this one below, from Slovenia.

Cave dipluran, Divaška cave, Slovenia, April 2017

 

The Japygoidea have adapted, pincer-shaped cerci, as shown in the photos below. The pincers are fully functional and are used to hold down prey. The photo shows an undescribed cave species from the South Island of New Zealand. 
Some members of the predatory Japygoida can reach up to 60mm, but most diplurans are around 2-5mm.

 
          Undescribed cave Burmjapyx species, Takaka hill, Nelson, NZ

          Undescribed cave Burmjapyx species, Takaka hill, Nelson, NZ

          Japygidae, Haida Gwaii, British Columbia, Canada

Projapygoidea are the third superfamily, and are far less studied, due to the difficulty in finding them. Annoyingly, I don't have any photos.
Recent studies have found some genetic linking to Campodeoidea, rather than the morphological missing link between Campodeoidea and Japygoidea as was once suspected. Even so, they do share different attributes from both of the two other superfamilies.
They also have some unique adaptions, such as two abdominal spinning glands on the ends of their shortened, cone-like-like cerci. The spinning glands produce threads, used to immobilise prey, as if pincers or jaws weren't enough.

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Diplura


Dipluran, Melbourne, Australia, Jan 2016

Diplura


Dipluran, Melbourne, Australia, Jan 2016

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Diplura


Dipluran, Tairua, New Zealand, Feb 2014

Diplura


Dipluran, Tairua, New Zealand, Feb 2014

 

While diplurans all show adaptations to soil or cave life, being sightless and lacking pigment, some species like this one above, from New Zealand, do have copious amounts of yellow pigment probably taken up through diet.