It’s Independence Day in the USA and freedom is always worth celebrating, so here is a somewhat gaudy mite celebration of July the 4th. This mite is a predator, probably specializing in nematodes and other soft-bodied prey (based on the few species that have been studied), and the family is very well represented in the Northern Hemisphere, especially in boreal and montane systems. This particular mite was collected by a colleague from Idaho and sent to me in Australia to help in producing a key to families.
Most of my mite art gallery is comprised of Australian mites, but a few yanks have made it into the mix. I can’t go beyond family for this mite, because the Zerconidae is absent from Australia and I’m not familiar enough with its representatives to put a name on it from a lateral view. Actually, even when they are on slides, I have difficulty putting names on most Zerconidae. The family is extraordinarily diverse in the Northern Hemisphere with about 37 genera and subgenera currently recognized. Unfortunately, as yet no one has pulled the literature together into a coherent whole, so the novice must deal with a plethora of languages, generic concepts, chaetotactic nomenclature, and proliferating hairs.
Chaetotaxy – the taxonomy of setae – is one of the most useful tools in the morphological analysis of mites. ‘seta, setae’ – is a fancy term for ‘hair, hairs’. I sometimes forget that students don’t necessarily know this and it takes a few minutes of uncomprehending stares to remind me to explain, but the term is used primarily for the hair-like mechanoreceptors that jut out all over the body and appendages of arthropods. Like a cat’s whiskers, setae use contact to pass information to a mite’s nervous system about what is around them. In this zerconid, the setae on the dorsal shield are short and bushy – densely covered in short, barb-like processes. Setae can take all kinds of forms from simple, needle-like hairs to highly branched, tree-like structures. One likes to think that these various forms have somewhat different functions, but supporting data is rare.
For most mites, every seta has a name, or rather several names, since there are usually two or three major systems in the literature for any particular group – a taxonomic Tower of Babel. Zerconids can be especially confusing because they appear to be basal to one of the major radiations of mites (the gamasine Mesostigmata) and like many ‘primitive’ groups, tend to have lots of structures. In the Zerconidae this has been complicated by a tendency to multiply their setae, making assigning a name to any particular seta somewhere between difficult and arbitrary. Fortunately, a Canadian (Lindquist) and a Spaniard (Moraza) have been working together to make sense of the Zerconoidea and seem to have made excellent progress. Now, if they would only take the time to produce a decent key to genera, I could start handing out names.