Minute Creatures (Mighty Mites)

The other day one of my work companions showed me a strange creature (so he thought) in an equally strange structured object he had put on the work bench. He kept saying: "Its moving". Looking at the obviously dead Sassafras seed capsule, I wondered what he was on about. Then I looked more closely! Sure enough, there were things moving around in there.
As I have indicated, the main object was easy enough to work out. It was the seed capsule from a Sassafras Trees. In this case the whole seed capsule had fallen from a Sassafras tree.

The local Sassafras trees flowered very heavily last spring. This is the result. The Sassafras seeds have been blowing around us all the time, over the last two weeks, and if one is house painting, it is a challenge to keep one's work clean from these hairy seeds, which blow around so profusely on the wind. As you can imagine, they stick to wet paint very readily. Annoyingly so.

Loose Sassafras seeds blown onto the ground.

Each seed is in a soft shell, attached below the hairs, which allow the seed to be blown on the wind, sometimes for hundreds of metres.
Inside the seed capsule (Top image above) were lots of tiny dark red-brown creatures.
As with yesterday's posting, a leg-count seemed in order: Six legs for insects, eight legs for Spiders, Ticks and Mites. Well, try as I might I cannot get 8 legs on these creatures, yet, it is pretty obvious that they are some kind of Mite.
They look like over-bloated micro-sized Spiders similar in shape (only) to the familiar Red-backed Spider. That's about the best I can do to describe them.

Apparently they feed on vegetable material, or certainly they are feeding within vegetable material. But perhaps they are hunting ever-smaller creatures. They were very active, scrambling through the hairs of the unreleased seeds in the leathery capsule of the Sassafras tree.

In case you are wondering about Mites, (being related to Spiders, but being "vegetarians") read this:

• "The only group of arachnids that has managed to break out of the predatory habit on a large scale is the mites, which have diversified into an extraordinary range of niches. Many are still predatory, but there are also thousands of species of plant feeders, fungivores, saprophytes, pollen and nectar feeders, microbial filter feeders, and internal and external parasites on a wide range of vertebrates and invertebrates."
• Source: http://www.australasian-arachnology.org/arachnology/acari/
  

My creatures are about 2mm long, with very high set body and a triangular shaped head and mouth arrangement (the "capitulum"). The body is extremely round ("bloated" as I said) (It is called the "idiosoma")

Note the protruding "v" shaped head portion
(partially hidden at top left of the Mite)

Their legs are all located in towards the front of the body, in a way which almost seems make them look overbalanced. Yet they manage to scramble through the dense hairs of the seeds with nimble ease.

Larval mites are usually hexapod (6 legs); nymphs and adults usually octopod (8 legs). (Wikipedia)
Once again, there's that issue of juvenile stages of various multi-legged creatures developing their full sets of legs later in life, as Bob Mesibov explained in the "comments" section yesterday. That process is called "anamorphosis", and the adjectival form is "anamorphic". So, with six legs, but looking and behaving like Mites, I conclude that these are larval stage Mites.

I mentioned that these are large Mites, simply because many (most) species of mites are so small that they are invisible to the naked eye. Many are microscopic creatures which parasitise airways of birds (notably the endangered Gouldian Finch) and the ears of dogs and cats. That same group of Mites (as the dog and cat ear mites - Sarcoptiformes) also causes Mange in Wombats.

Click to enlarge this next image.
This is the rear view of the Mite.
(it is walking on its side away from camera)
You can clearly see a lateral groove running around the side and rear.

That groove, is called a "peritreme - a groove or gutter on the surface connecting to a stigmatal opening. In Mesostigmata the peritremes are lateral and run above the coxae of the legs and usually run to near the anterior margin of the idiosoma, but they may be very short or vestigial." Source: Glossary of Acarine Terms

I think my Mites might belong to the order Holothyrida.
(Grateful for any advice to set me straight - THIS IS NOT MY AREA OF SPECIALISATION).

The website for the Australasian Arachnology Society (yes folks, it is 2010, of course they have their own Webpage!) tells me that:

• "The order Holothyrida includes large mites (larger than 2 mm) with a heavily sclerotised and highly-arched body, which feed readily on dead arthropods (Walter and Proctor 1998). The order includes about 25 species in three families, and has a Gondwanan distribution. Only three species have been described from Australia, all in the family Allothyridae (van der Hammen 1983), but many other undescribed species have been collected and await study."

In the Lucid Key to Invasive Mites, the illustrated member of the order Holothyrida is a member of the genus Allothyrus.

Here is an Electron Microscopic image of Allothyrus - Photo by D.E.Walter, Colorado State University, from the Lucid Key to Invasive Mites. (details below).

Note the body shape, and the prominent peritrematal groove (at rear).
Mite: Allothyrus

Sources: Walter, D.E., Invasive Mite Identification: Tools for Quarantine and Plant Protection, Lucid v. 3.3, last updated July 24, 2006, Colorado State University, Ft. Collins, CO and USDA/APHIS/PPQ Center for Plant Health Science and Technology, Raleigh, NC.
[date accessed 27.04.2010] -
http://www.lucidcentral.org/keys/v3/mites/