Continued Adventures with Rake-legged Mites

Dorsal view of Neocaeculus kinnearae; photo modified for Taylor (2014).

It's been a noteworthy couple of weeks here at chez CoO. My contract at the university has reached its end, and I've become a Free Agent ('free' as in 'I don't get paid for any of this stuff'). That bit in the sidebar where I describe myself as "an entomologist working on the identification of terrestrial invertebrates" is, for the nonce, more of an aspiration. Or, to put another way, a lie. And my lunch breaks have gotten a lot more generous. Time will tell how long this state of affairs will continue, but in the meantime, there's still research to be done and papers to produce. Which segue's nicely into the subject of today's post: my newest paper, "Two further Neocaeculus species (Acari: Prostigmata: Caeculidae) from Barrow Island, Western Australia".

Back in December, I commented on the publication by myself and my colleagues of the rake-legged mite Neocaeculus imperfectus. In the comments for that post, I indicated that N. imperfectus was not the only new rake-legged mite species that I had on hand*. As it turns out, there was a total of five different species of caeculid in our collection (including N. imperfectus). Two of these were species that had already been described by Coineau & Enns (1969), but two more were new. The first of these I have dubbed Neocaeculus kinnearae, after my colleague Adrianne Kinnear, to whom I owe all of my understanding of mites. Adrianne first identified many of the Barrow Island mites, and trained me in mite identification prior to her recent retirement. Neocaeculus kinnearae is very similar to a species originally described from the Kimberley region of northern Western Australia, N. knoepffleri (some of you not familiar with Australian geography may still know the Kimberley as one of the few regions that diamonds come from). The two primarily differ in size (N. kinnearae is distinctly smaller) and while the large leg-spines in N. knoepffleri end in sharp points, those of N. kinnearae are blunter. Interestingly, N. knoepffleri is also present on Barrow Island, which did lead me to wonder if the specimens I ended up assigning to N. kinnearae might be just smaller individuals of N. knoepffleri. But I have seen several specimens of both from Barrow by now, and I'm yet to see any overlap between the two, so I do think that they are both good species.

*You may wonder why, if I knew that there was more than one species present, I didn't just put them all in the one paper. The reason was that, because I had never prepared a mite taxonomic paper before, I wanted to just do the one species at first as a test run, and then do the others once I felt a bit more confident that I knew what I was doing.

Neocaeculus knoepffleri also has a particular claim on my affections in that I've seen it alive. This is a bigger deal than it sounds: caeculids are cryptic and slow-moving, so observing them in the field is notoriously difficult. I already explained in my earlier post how I've never seen Neocaeculus imperfectus out and about, despite it turning up in samples in numbers that suggest absolute plagues of the things. But on my last trip to Barrow back in March, we were out collecting at night near the shore when I spotted a small grey point on a grey rock move slightly. Closer inspection revealed a caeculid sitting on the rock with spiny front legs outstretched, in the classic caeculid ambush pose. If I moved my forceps close to it, the mite would turn towards them as if warding them off. Having found one, I looked a bit further, and found several more, all perfectly camouflaged against the rock.

Dorsal view of Neocaeculus nudonates; original version of photo used in Taylor (2014).

The second new species was the smallest caeculid I had seen from Barrow so far, but was none the less remarkable. For a start, it didn't have the slender spines on its front legs of other rake-legged mites; instead, the spines were modified into rounded paddles. There are a few other caeculids known to have this feature (one of them, Neocaeculus bornemisszai, is another Kimberley species now also known from Barrow). Where their habits are known, it seems to be an adaptation for digging in sand, something that I can assure you Barrow Island has no shortage of. The other interesting feature of the new species is that the dorsal plates that usually cover the rear half of the body in other caeculids are unusually small. It was the appearance given by these small plates that inspired the name I gave this species: nudonates, from the Latin nudus, naked, and nates, buttocks. This is, literally, the bare-arsed mite.

So Barrow Island is now officially home to five different species of caeculid mite (and shortly after submitting this paper, I came across specimens of a sixth). While only one of these species has actually been observed alive, we can still infer some things about the likely habits of the others. Two, Neocaeculus bornemisszai and N. nudonates, are probably diggers of some sort. They may prefer different substrates: while N. nudonates has the afore-mentioned reduced plates, N. bornemisszai is more heavily armoured than usual. There may be a difference in preferred substrate between N. knoepffleri and N. kinnearae as well, to explain the blunter leg spines of the latter. In the paper, I suggested that N. imperfectus was probably a climber on vegetation, to explain it mostly being found in suction samples while the other species all came from pitfall traps. Since the paper was submitted, I have seen a few N. kinnearae specimens in suction samples, but I still think that it is most likely not a climber because these have been few and far between.

The other main point to be made is that there are probably a lot more caeculids out there than we realise. Though only eight species of caeculid have been recorded from Australia so far, Barrow Island is home to at least six (one of which may or may not be a further undescribed species). Caeculids are generally regarded as associated with warmer, drier habitats, and Australia is almost entirely warmer, drier habitat. I would not be surprised if, once we looked further, we would find a lot more undescribed caeculids out there.