Zerconids

Slide-mounted male of Zercon gurensis, copyright Holger Müller.

The animal depicted above is a mite of the Zerconidae, one of the numerous families in the major mite clade known as the Mesostigmata. This family is mostly found in soil habitats such as leaf litter, mosses, decaying vegetation, or occasionally in animal nests (Lindquist et al. 2009). The zerconids are restricted to the Northern Hemisphere and are most diverse in temperate to Arctic regions; those species found in tropical parts of the world are restricted to high altitudes away from the hot lowlands (Ujvári 2012). Like many other Mesostigmata, they have the dorsal surface of the body mostly covered by shields of hardened cuticle. In most zerconids, separate shields cover the front (podonotal) and rear (opisthonotal) sections of the dorsum; the opisthonotal shield wraps around the rear margin of the mite and forms a continuous unit with the ventrianal shield that usually protects most of the underside of the mite behind the legs. Among the most noticeable features of the zerconids are two pairs of large openings near the rear of the opisthonotal shield (the four orange-segment-like structures in the photo above). These represent the openings of secretory glands, but I don't know if it has been established just what they're secreting; comparable structures in other mites may secrete pheromones, or defensive chemicals, or oils that prevent debris from sticking to the body. Other features of the zerconids include slender, relatively simple chelicerae that lack the modifications seen in the males of some other Mesostigmata, and peritremes (grooves on the underside of the body that channel air to the openings of the respiratory stigmata) that are relatively short. These peritremes are longer in zerconid nymphs, but become shortened when the mite moults to maturity.

Zerconids are another of those mite groups where the vast majority of what has been written about them relates to their basic taxonomy, with little yet known about their natural history. Several genera of zerconids are recognised, distinguished by features such as the shape of the body's various shields and the appearance of various setae. The form of their chelicerae indicates that zerconids are predatory like many other Mesostigmata. Because they are mostly found at ground level rather than on vegetation they have not attracted the economic interest of other predatory mites, but those few species that have been observed feeding were chowing down on nematodes. Mating does not appear to have been directly observed in zerconids, but again their anatomy and comparison with other mesostigs allows us to infer that the male fertilises the female by using his chelicerae to pass a spermatophore from his own genital opening on the underside of the body between the legs to hers. Where she then lays her eggs, and how her offspring spend their time to maturity, seem to be questions still awaiting an answer.

REFERENCES

Lindquist, E. E., G. W. Krantz & D. E. Walter. 2009. Order Mesostigmata. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3rd ed. pp. 124–232. Texas Tech University Press.

Ujvári, Z. 2012. Draconizercon punctatus gen. et sp. nov., a peculiar zerconid mite (Acari: Mesostigmata: Zerconidae) from Taiwan. Opusc. Zool. Budapest 43 (1): 79–87.

Hastocularis: A Fossil Harvestmen Allows Us to See

Sometimes the fossil record just gives us a gift, something that moves our understanding to an all-new level. One such gift saw publication a couple of years ago, but unfortunately I didn't have time to write about it then. I think it's about time I corrected that lacuna.

Reconstruction of Hastocularis argus, from Garwood et al. (2014).

By this point in time, we have a pretty good understanding of the basal framework of harvestmen evolution. The mite-like harvestmen of the Cyphophthalmi are well established as the sister group to all other Opiliones (which form a clade called the Phalangida). Unique features of the Phalangida include an intromittent penis in the males (phalangids are one of the few groups of arachnids to possess such a feature) and a central eyemound with a single pair of eyes. The Cyphophthalmi are more heavily armoured than most phalangids, and have a characteristic pair of raised cones (the ozophores) on either side of the carapace near the front that support the openings of odour-producing repugnatorial glands. Until recently, it was thought that most Cyphophthalmi lack eyes, but tiny, lens-less remnant eyes are now known to be present at the base of the ozophores in many cyphophthalmid subgroups.

There had long been questions about the nature of the cyphophthalmid eyes. The original arachnids possessed multiple pairs of eyes, and there is a good case to be made that the basal arrangement for arachnids as a whole is a single pair of larger median eyes in the middle of the carapace, and a number of pairs (up to three) of smaller lateral eyes at the margin. In some arachnid groups the median eyes have been lost; in others, the lateral eyes have become reduced in number or lost. In spiders, the lateral eyes have become enlarged and shifted about so the lateral/median distinction is less applicable (for the record, the posterior median eyes in spiders correspond to the original median eyes). Mites, of course, being mites, mess the whole system up entirely. Most mite eyes correspond to the original lateral eyes, but some mites possess a single median eye whose relation to the original arachnid median eye pair is up for grabs.

Phalangids, with their single central eyemound and single pair of eyes, had obviously kept the original median eyes and lost the lateral eyes. But what had happened with the Cyphophthalmi? Did their single pair of eyes near the edge of the carapace represent a single remnant pair of lateral eyes, or did they correspond to the median eyes of other Opiliones? It should be noted that some derived groups of undoubted Phalangida have lost the eyemound and have their eyes sitting directly on the carapace, and in some cases these unraised eyes may be widely separated. Arguments for both interpretations of cyphophthalmid eyes had been put forward by different authors, but the matter had certainly not been decided.

A representative member of Phalangida, Platybunus pinetorum, showing the central eyemound, from Opiliophilia.

That was until the description by Garwood et al. (2014) of Hastocularis argus, a remarkably preserved fossl harvestman from the Carboniferous of France. The appearance of this animal was established in some detail by the use of microtomography, allowing a number of details about it to be established. It was a heavily armoured animal with long legs, and like modern Phalangida it possessed a central eyemound on which there had been a pair of eyes (the eyes themselves were not preserved, but the sockets that had originally contained them were). The use of microtomography also allowed the identification of an intromittent penis like a phalangid. But Hastocularis also possessed a pair of raised ozophores like modern Cyphophthalmi, and at the base of those was preserved another socket indicating the presence of a second pair of eyes. There really could not be a more perfect answer to the cyphophthalmid eye question: the immediate ancestor of the Opiliones possessed two pairs of eyes, and the eyes of Cyphophthalmi do indeed correspond to the lateral eyes of other non-harvestmen arachnids and not to the median eyes of phalangids*.

*Pedantically speaking, Hastocularis is not the first four-eyed taxon assigned to the Opiliones. In 1875, an Austrian biologist by the name of Stecker described a remarkable animal from the Sudeten Mountains of Bohemia under the name of Gibbocellum sudeticum. Gibbocellum bore an overall resemblance to the Cyphophthalmi, except for possessing two pairs of eyes on raised cones, as well as two pairs of spiracles (other Opiliones possess a single pair). Despite enthusiastic searches, no other naturalist was ever able to find further specimens of Stecker's species, and at least one author suggested that it might be a poorly interpreted pseudoscorpion. However, a close criticism of various irregularities in Stecker's publications on Gibbocellum eventually lead Hansen & Sørensen (1904) to the conclusion that it had not merely been misrepresented, but was in fact a complete fabrication on that author's part.

A phylogenetic analysis of Hastocularis lead Garwood et al. (2014) to believe that it was more closely related to Cyphophthalmi than to Phalangida; together with another Carboniferous fossil species, Eophalangium sheari, they placed it within a new taxon Tetrophthalmi (meaning, of course, 'four eyes'). The main features cited in support of this relationship were the complete fusion of the dorsal surface (the only other harvestmen to show this feature are a southeast Asian family, the Oncopodidae, who are too deeply nested within the Phalangida to be a likely direct relative of Hastocularis) and the genital opening being a broadly open gonostome (in Phalangida, the genital opening is covered by an operculum). This implies that the immediate ancestor of all Opiliones was relatively long-legged, with the short legs of Cyphophthalmi a derived feature. However, I personally find the presence of an intromittent penis in Tetrophthalmi (it is also known to be present in Eophalangium) somewhat problematic in this regard. As noted above, the phalangid intromittent penis that directly injects sperm into the female ovipositor is highly unusual among arachnids. Cyphophthalmi do possess a penis-like structure (called the spermatopositor) but it is much shorter than in any phalangid and does not function as an intromittent organ. Instead, Cyphophthalmi males produce an encapsulated spermatophore that is attached by the spermatopositor to the female's underside, a more typical sort of arrangement for arachnids as a whole. An intromittent penis in the cyphophthalmid stem group would imply that Cyphophthalmi somehow reverted towards a more primitive-seeming reproductive arrangement at some point in the past. One possibility is that the penis of Tetrophthalmi did not function in exactly the same manner as that of Phalangida: perhaps tetrophthalmids still produced a spermatophore but were able to insert it more deeply in the female than Cyphophthalmi? Another possibility may be that Tetrophthalmi are stem-phalangids rather than stem-cyphophthalmids; only further analyses can possibly tell us more.

REFERENCES

Garwood, R. J., P. P. Sharma, J. A. Dunlop & G. Giribet. 2014. A Paleozoic stem group to mite harvestmen revealed through integration of phylogenetics and development. Current Biology 24: 1017–1023.

Hansen, H. J., & W. Sørensen. 1904. On Two Orders of Arachnida: Opiliones, especially the suborder Cyphophthalmi, and Ricinulei, namely the family Cryptostemmatoidae. University Press: Cambridge.

New Zealand Harvestmen: Please Help

The cave-dwelling Forsteropsalis photophaga, a remarkable harvestman species described in Taylor & Probert (2014).

As regular readers of this blog will be well aware, I've been working for several years now, off and on, on the taxonomy of long-legged harvestmen of the family Neopilionidae from Australia and New Zealand. In the past few years, this has been a bit more off than on: the necessities of earning a crust have meant that I haven't had the time to dedicate to full-time harvestman research. Nevertheless, I've been putting things together here and there where I can and an enormous amount of progress has been made. Back when I first decided to investigate this group of animals in 2000/2001, there were a handful of named species, often with descriptions amounting to nothing more than a couple of vague lines, all but unidentifiable in practice. Over time, I've redescribed each of these species in turn, as well as describing and naming a pile of new ones. We've learnt things about these animals we never knew before, such as the presence in many populations of a remarkable divergence within males to the extent that to the uninitiated they might be (and have been) mistaken for completely different species. We've seen the incredible range of forms in this group, from long-jawed monsters like to one at the top of this post, to heavily armoured cryptic soil-dwellers like in this photo by Stephen Thorpe.

After many years, I feel I'm finally approaching the point where I can put the finishing touches on my revision of the New Zealand neopilionids (for a given value of 'finish', of course, because there is no group of organisms for which the work is ever truly finished). Ideally, I would like to publish something incorporating a complete overview of this group of animals, a complete guide to all the known species offering a one-stop-shop to allow anyone, anywhere to confidently identify any specimen that might come to their hand. It's also important to me that I publish this guide in an open-access format so that it's also available at any time.

But to do that, I need your help. In order to be able to travel to the New Zealand museums that hold types and other crucial specimens that I need to examine, and to cover the publication fees of the resulting product, I've started a crowdfunding drive. Head over to https://experiment.com/projects/how-can-we-distinguish-species-of-new-zealand-harvestmen and you'll be able to support my research, follow the results as they become available, and receive full acknowledgement in the resulting publication(s). Even if you can't support me directly myself, you would be helping immensely if you inform others of my campaign, whether through social media, in person, or any other medium that makes itself available. Together, we can bring this truly incredible group of animals the recognition they so richly deserve!

If you want to see some of my work on harvestmen that's already come out, check out the links below:

Remarkable things
Possibly the coolest thing I had published this year
Score one for biogeography
How to wipe out a family
The saga of Forsteropsalis fabulosa
More on the New Zealand Opiliones
Bye, bye, Spinicrus
The eater of light
New Zealand fills a biogeographical gap

New Zealand Fills a Biogeographical Gap

Lateral view of the holotype (and only known specimen) of new species Americovibone remota.

Taylor, C. K. 2016. First record of a representative of Ballarrinae (Opiliones: Neopilionidae), Americovibone remota sp. nov., from New Zealand. Journal of Arachnology 44 (2): 194–198.

New paper, and new species of phalangioid harvestman, out! And one that I'm pretty excited by, even if the vagaries of time allocation mean that I haven't been able to get the post out until a couple of weeks after it happened. After several years of studying New Zealand's long-legged harvestman fauna, I have to confess I was getting a bit complacent about. I certainly knew that I had not seen every species that the country had to offer, but I still thought that there were no real surprises remaining. The overall outline had become clear; any species of long-legged harvestman remaining to be described from New Zealand would be fairly closely akin to those already known.

Oh boy, was I wrong.

At some point last year (or maybe the year before), I was sorting through a jarful of specimens that were still waiting on my attention. In one of the vials, its contents collected in a remote part of the south-west South Island, was a tiny, wispy specimen that I at first glance paid little mind to. Newly-hatched juveniles are not uncommonly collected; they are almost always unidentifiable and end up being just chucked back into the jar never to be looked at again. Nevertheless, I pulled the specimen out to confirm that my first impression was correct. I placed the specimen in a dish under the microscope and glanced through the eyepiece. Then looked again, my eyes doubtless boggling. I may have even sworn a little. Not only was the specimen not a juvenile but fully adult, it was something I had long given up on seeing from New Zealand: a ballarrine.

Dorsal view of the main body.

The Ballarrinae are an unusual group of harvestmen that were not recognised until fairly recently. The group was named by Hunt & Cokendolpher in 1991 with species found in South Africa, Australia and South America. The South African species Vibone vetusta was the only one described prior to Hunt & Cokendolpher's (1991) paper, and until now no further species had been described since. The main reason these animals were overlooked previously is probably their size: ballarrines include some of the smallest of all harvestmen (the specimen I was looking at, for instance, has a central body only a bit over a millimetre long). Ballarrines differ from other harvestmen in the form of their pedipalps which are relatively long and have the patella much longer than the tibia (the converse is usually the case). Whereas other phalangioid harvestmen have the patella and tibia of the pedipalp more or less in a straight line or have the tibia bent slightly downwards, Hunt & Cokendolpher (1991) were struck by how the ballarrines had the tibia reflexed upwards relative to the patella. Ballarrine pedipalps also lack a terminal claw, and have only a relatively few glandular hairs instead of the denser covering of simple hairs found in other harvestmen. As noted in an earlier post and paper that I was associated with (Wolff et al. 2016), the overall pedipalp form is adapted for preying on small animals such as springtails: the long pedipalp acts like a tentacle that can be whipped forward to trap prey with its sticky hairs.

Until this point, New Zealand had been a puzzling gap in the Ballarrinae's otherwise classic Gondwanan distribution (long-term readers may recall that this is the second time I've seen a puzzling biogeographical lacuna filled). I didn't have any idea why that should be absent but even after looking at probably thousands of harvestmen specimens from all corners of the country I still hadn't seen any. Hence my immediate excitement about the find, but said excitement was also leavened with a certain degree of caution. Harvestmen taxonomy is heavily dependent on features of the males (particularly the male genitalia) with females of closely related species often being indistinguishable. Unfortunately, the only specimen of New Zealand ballarrine I had on hand was female. Sorting through the remainder of the collection I was working on failed to turn up any more. I even considered whether I could wrangle a trip to the original collection locality to see if I could find more specimens, but that proved unfeasible. The ballarrine had been collected by J. Dugdale in 1980 at a spot called the Dart Hut, which lies at the summit of the Rees-Dart walking track in Mount Aspiring National Park. This is a pretty isolated part of the country with no permanent population and no nearby roads. Travelling to the Dart Hut by foot takes a minimum of two days each way; the usual time taken to travel the Rees-Dart is five days (its supposed to be a nice hike that travels through similar terrain to the more famous Milford Trail without the massive crowds of the latter). What is more, at the time I was looking into it, the Rees-Dart was closed until further notice due to flooding earlier in the year taking out one of the bridges along it. Nevertheless, I eventually decided that the value of publicising the presence of this significant group in New Zealand outweighed the risk of not yet being able to confirm male morphology. Unfortunately, the nature of the specimen (spindly legs everywhere!) meant that I found myself unable to get good photographs and the resulting paper had to be illustrated with (always somewhat ropey when I do them) hand-drawn illustrations; nevertheless, the best photos I got are here in this post.

The tentacle-y pedipalp of A. remota is considerably longer than the central body; it's nearly as long as one of the legs!

Fortunately, sexual dimorphism within ballarrines tends to be low. I was very interested to see that the New Zealand ballarrine was more similar to the South American species Americovibone lanfrancoae than to any of the Australian species; so much so, in fact, that I ended up assigning it to the same genus as Americovibone remota. Americovibone lanfrancoae is also a very rare species, being described from only two known specimens from the Tierra del Fuego region. The most obvious difference between A. remota and A. lanfrancoae is that, in the former, the tibia of the pedipalp is not reflexed back above the patella as in every other ballarrine but is bent slightly downwards in a more standard position for phalangioids. This has some very interesting implications for ballarrine phylogeny. A molecular phylogenetic study of long-legged harvestmen by Groh & Giribet (2014) that included two ballarrines (the South African Vibone vetusta and the Australian Ballarra longipalpis) failed to unite the two as a clade. If accurate, this result would require the distinctive ballarrine pedipalp to have evolved on more than one occasion. The observation that A. remota may retain a more plesiomorphic pedipalp morphology could provide some correlation for this possibility.

But if Ballarrinae are indeed present in New Zealand, why are they apparently so rare? Part of the reason may be to do with habitat. Both the New Zealand and South American species of Americovibone are known from forests dominated by Nothofagus, southern beech. This tree genus is widespread in upland and colder parts of New Zealand. A bit north of the collection locality for A. remota, however, is an area where the beech forests disappear for a distance of a couple of hundred kilometres: this has been referred to as the "Nothofagus gap". Studies on other groups of organisms show that this gap is a significant one for New Zealand biogeography, with many beech-associated species restricted to one side or the other of the gap. Could A. remota be a specialist of the south-west beech forests of the South Island? If so, it is unique to one of New Zealand's least known corners.

REFERENCES

Hunt, G. S., & J. C. Cokendolpher. 1991. Ballarrinae, a new subfamily of harvestmen from the Southern Hemisphere. Records of the Australian Museum 43: 131–169.

Wolff, J. O., A. L. Schönhofer, J. Martens, H. Wijnhoven, C. K. Taylor & S. N. Gorb. 2016. The evolution of pedipalps and glandular hairs as predatory devices in harvestmen (Arachnida, Opiliones). Zoological Journal of the Linnean Society 177 (3): 558–601.

Harvestmen and their Hairy Pedipalps

A selection of harvestmen, showing a variety of pedipalpal morphologies, from Wolff et al. (in press). The upper two are Laniatores with spiny pedipalps; the lower two are Palpatores with leg-like pedipalps.

Wolff, J. O., A. L. Schönhofer, J. Martens, H. Wijnhoven, C. K. Taylor & S. N. Gorb (in press) The evolution of pedipalps and glandular hairs as predatory devices in harvestmen (Arachnida, Opiliones). Zoological Journal of the Linnean Society.

I'm happy to say that a new paper on which I am an author has just been made available. It's been a while (long-term unemployment has not profited my publication record, I must admit), but there are a few things still bubbling below the surface. This last entry is a study of the evolution of harvestmen's pedipalps, the more-or-less leg-like appendages on either side of the mouth that they use for collecting, capturing and manipulating food, and particularly the sticky hairs that many harvestmen have on them. My part in this publication was fairly minimal: I provided specimens and data on Neopilionidae, and assisted with the English-language composition. Full credit goes to my co-authors, particularly our lead author Jonas Wolff who drove it all.

I've learnt some interesting things myself working on this paper. When I first started researching harvestmen, most of the sources I read described them as scavengers, content to get by on decaying remains that they chanced upon in their wanderings. For some harvestman species, that is indeed their chosen diet. But some other species are not content with mere leavings, preferring their meat fresh and wriggling. These species are active predators, using their pedipalps to seize springtails and other small invertebrates. As a result of their use for this and other activities, harvestmen pedipalps show a wide range of shapes and sizes: some simple and presumably multi-purpose, others strikingly modified. Many species (particularly within the Laniatores, or 'short-legged' harvestmen) carry long spines on the pedipalps, and one might presume these to be the more blood-thirsty harvestmen. But, as reported by Wolff et al., there are many species no less active in their hunting (if not even more so) that not only have their pedipalps unadorned with spines but have even lost or reduced the claws that usually tip the pedipalps. What is going on here?

The answer lies in these species' possession of an alternative to spines: glandular setae. These are little hairs attached to a gland secreting a sticky glue that sits in a globule on a cluster of micro-hairs at the end of the seta, and are found in various species of the Palpatores ('long-legged' harvestmen). In some species the micro-hairs may be on one side, like a tooth- or a boot-brush; in others they may form a ring around the end. Using glue to capture prey can be even more effective than using spines or claws: springtails and such are often covered with scales or other loose structures that can slide off when the animal is seized, allowing the prey to escape and leaving the would-be predator with a handful of dust. Attacking the prey with multiple points of sticky glue, however, increases the chance of holding onto it, as the glue works around the scales and adheres to the body.

Two harvestmen showing convergent 'tentacle' pedipalps, the dyspnoan Mitostoma chrysomelas on the left and the ballarrine Ballarra longipalpis on the right, from Wolff et al. (in press).

Most harvestmen have not gone the whole hog for glandular setae; there is presumably scope for compromise with the use of the pedipalps for other purposes such as mating (the genital opening for harvestmen is around the mid-point of the underside of the body, so harvestmen mate 'face-to-face' and may use the pedipalps to hold onto each other). Many Palpatores possess a smattering of glandular setae at certain points on the inner side of the pedipalps only, and otherwise have a fairly underived leg-like pedipalp with a well-developed claw. One particularly interesting example that I hadn't heard of before was the Asian species Metagagrella minax, which possesses glandular setae as a juvenile but progressively loses them as it matures. Nevertheless, there are two groups, the Dyspnoi and Ballarrinae, that possess what Wolff et al. dub the 'tentacle' form of pedipalp: the pedipalps are elongate with glandular setae along the entire length and lack the claw entirely. The Dyspnoi is a purely Northern Hemisphere lineage, whereas the Ballarrinae are restricted to the Southern Hemisphere. The two groups sit nested on opposite sides of the primary divide within Palpatores, so there is no question that the 'tentacle' pedipalp has evolved independently in the two groups (which is also reflected by differences in each in the relative proportions of the segments making up the pedipalp). However, there is a bit of a question about whether the 'tentacle' has appeared even more often: Wolff et al. assume a single origin of the Ballarrinae but this has recently been cast into doubt. This is a question that interests me directly because of something else I've currently got on the boil... but that's a topic for another day.

Phytoseiids and the Importance of Taxonomy

Gupta's (1975) original figures for Amblyseius syzygii.

For this week's semi-random post, I drew the mite species Amblyseius syzygii. Or perhaps that should be Typhlodromips syzygii, as it's more likely to be designated now. Typhlodromips syzygii is a member of the Phytoseiidae, a diverse family of about 1600 known species of predatory mite. Despite, or perhaps because of, their being an economically significant group (more on that in a bit), phytoseiids have been somewhat plagued by competing nomenclatural systems. Until relatively recently, they were predominately classified into just a few, very large genera. In the last couple of decades, however, there has been a move towards a much more finely divided classification, but you will still find many sources that will continue to use the more conservative system, particularly among those with more of an economic interest in the group than a taxonomic one.

It is as a result of this taxonomic changing of the guard that syzygii, once nestled in the broad genus Amblyseius, has been separated as part of a genus Typhlodromips that was placed by Chant & McMurtry (2005) in an entirely separate tribe from its former host. The genera are separated by features such as the number, shape and proportions of the dorsal setae, and the arrangement of macrosetae on the legs. In fact, counting setae seems to be a major part of taxonomy in the Mesostigmata (the major mite group to which the phyoseiids belong) as a whole, which is part of why this is one group of mites I've so far had difficulty in coming to terms with. Counting setae sounds like it should be easy, but in my experience it's usually not. Especially when the animal is slide-mounted, requiring you to move to focus on the microscope up and down in order to see all the setae, leading to confusion about whether a given visible setae is one you've already counted or not.

Anywho, even after the split, T. syzygii is one of about sixty species in its genus. It was first described in 1975 from West Bengal, from a specimen collected on a jambul tree Syzygium cumini (Gupta 1975; hence the species name). Since then, it has been recorded all around southern and eastern Asia, and from a wide variety of different plants. Distinguishing features of the species include (again) proportions of the dorsal setae, with T. syzygii possessing features such as a pair of large posterolateral serrate setae, as well as details such as the shape of the ventral plates on the body.

A related amblyseiid, Amblyseius swirskii, attacking a thrips. Copyright Steven Arthurs.

I referred before to the economic significance of phytoseiids. This is because a number of species in this family have been utilised as biocontrol agents for plant-feeding mites and other minute pests such as thrips. In some places, you can even buy commercially-produced satchels containing colonies of phytoseiids that can be hung in an orchard and allow the mites to disperse among your trees (arachnids in a bag, people, arachnids in a bag). Alternatively, industrial-size blowers may be used to fire clouds of mites across a crop. I have come across reference to Amblyseius syzygii as a predator of the tea red spider mite Oligonychus coffeae, a significant crop pest. The use of phytoseiids in pest control has, in turn, lead to a massive amount of research on phytoseiid distribution, prey preferences, and pesticide resistances (some phytoseiids can be applied in combination with pesticides that affect the target pest but not the phytoseiids). However, this has also required a lot of attention to phytoseiid taxonomy. For all that phytoseiid species may be obscenely difficult to distinguish, even closely related species may vary significantly in each of the aforementioned factors. For instance, Beard (1999) refers to a number of morphologically all-but-indistinguishable but behaviourally distinct species/populations/whatever that have been identified as the biocontrol 'species' Neoseiulus cucumeris. Some strains might be found only on low-growing plants and never on trees, others may be quite high above the ground. Some may cluster around the flowers of their host plants, others may prefer the fruits and/or young leaves. And they might differ in prey preferences: of two strains found in Britain, one would munch quite happily on the broad mite Polyphagotarsonemus latus, the other would refuse to touch it. Obviously, introducing the wrong strain in a pest control effort could lead to a lot of money being spent on a futile attempt.

REFERENCES

Beard, J. J. 1999. Taxonomy and biological control: Neoseiulus cucumeris (Acari: Phytoseiidae), a case study. Australian Journal of Entomology 38: 51–59.

Chant, D. A., &. J. A. McMurtry. 2005. A review of the subfamily Amblyseiinae Muma (Acari: Phytoseiidae): part VII. Typhlodromipsini n. tribe. International Journal of Acarology 31 (4): 315–340.

Gupta, S. K. 1975. Mites of the genus Amblyseius (Acarina: Phytoseiidae) from India with descriptions of eight new species. International Journal of Acarology 1 (2): 26–45.

Mites in Red Velvet

Adult Platytrombidium fasciatum, copyright Walter Pfliegler.

Mites in red velvet,
decorated with stripes.
Completing their diet,
hunting down eggs from flies*.

*With apologies to Justin Hayward.

Among the mites most likely to be seen by the casual observer are the various species of active predators known as red velvet mites. They grow to relatively large sizes for a mite (the species in the photo above can get up to 2.5 mm long), they are brightly coloured and they can often be seen moving about in search of food. As well as the colour, the name 'red velvet mite' refers to their dense covering of setae giving them almost a teddy-bearish appearance. There aren't many mites that could be described as cuddly, but these are arguably among them (at least as adults, as explained below).

Red velvet mites form a number of families in the mite clade Parasitengonina. Earlier posts on this site (here and here) have already described the somewhat complicated life cycles of parasitengonines, but to recap briefly: parasitengonines start their lives as parasitic larvae, followed by a dormant 'pupa-like' stage, followed by an active predatory nymph, then another dormant 'pupa', and finally the active predatory adult. Whereas differences between the active nymphs and adults are slight (kind of raising the question as to why the intervening dormant phase), differences between adults and larvae are significant. From their appearance alone, there is no way of telling whether a given larval form corresponds to a given adult, and connecting the two requires challenging indirect methods such as brood-rearing. Nevertheless, both forms are commonly encountered: not only are adults significant micro-predators, the larvae are often found attachned to insects and other arthropods. Some larval species, commonly known as chiggers, attack vertebrates such as humans and so are even more well-studied. Because of the resulting need to classify both adults and larvae without an easy way to connect the two, a kind of double taxonomy has developed with many parasitengonines. Adults and larvae are treated as if they were separate 'genera' and 'species', with separate names for each. Sometimes a larval 'species' may be successfully connected to an adult 'species' and the two can be synonymised, but many taxa remain that are known only from one or the other.

The genus Platytrombidium, belonging to the velvet mite family Microtrombidiidae, was established in 1936 on the basis of adults, but its larval form was not described until 2005. A number of species have been assigned to this genus from various parts of the world but, as a result of obtaining better descriptions of both adult and larva, Gabryś et al. (2005) restricted it to three species known from the Palaearctic region (Europe and northern Asia). Adult Platytrombidium are characterised by an even covering of stout, uniform setae covered with delicate setules; when alive, they are even more readily recognised from their transverse white stripes across the body. As adults and active nymphs, Platytrombidium fasciatum (the best-known species in the genus and the only one with known larvae) feed on fly eggs. Their larvae are also parasites on drosophilids and similar small flies, most often found attached to the dorsal surface of the abdomen (Gabryś et al. recorded one larva found attached to its host's eye).

Most of the confusion about the taxonomy of Platytrombidium has revolved around its relationship to the very similar genus Atractothrombium. For a long time, the only recognised difference between the two was whether the setae on the body were pointed (Platytrombidium) or blunt (Atractothrombium). Needless to say, this was not a very clear character, and might appear to vary even over the surface of a single individual. Nevertheless, Gabryś et al. (2005) found that they were able to distinguish the type species of the two genera by features of the adult palps and larval claws (Atractothrombium sylvaticum is also evenly dark red, lacking the white stripes of Platytrombidium fasciatum). They also differ in habits: both are predators and parasites of flies but whereas P. fasciatum is found in drier habitats such as gardens and parks, A. sylvaticum prefers damp habitats that flood regularly, such as reed beds and salt marshes.

REFERENCES

Gabryś, G., A. Wohltmann & J. Mąkol. 2005. A redescription of Platytrombidium fasciatum (C. L. Koch, 1836) and Atractothrombium sylvaticum (C. L. Koch, 1835) (Acari: Parasitengona: Microtrombidiidae) with notes on synonymy, biology and life cycle. Annales Zoologici 55 (3): 477–496.

Stygophalangium: Harvestman or Mite?

The original illustration of Stygophalangium karamani, from Oudemans (1933).

In 1933, the Dutch zoologist Anthonie Oudemans described what he believed to be a remarkable new species of harvestman. Based on two specimens collected from an underground spring in modern-day Macedonia and dubbed Stygophalangium karamani, Oudemans regarded this as a highly degenerate form as a result of its habitat: small, soft-bodied, and eyeless. It exhibited some significant differences to other harvestmen: in particular, the body lacked obvious signs of external segmentation. Also, its apparent aquatic collection point stood in direct contrast to the otherwise terrestrial habitats of other species. Nevertheless, Oudemans placed this unusual animal in a new family, the Stygophalangiidae, and suggested that its reduced morphology compared to other harvestmen might be compared to the position of Eriophyes (a plant-feeding, four-legged genus) among the mites. However, due to its anomalous character, subsequent authors have not paid much attention to little Stygophalangium. Mello-Leitão (1944) briefly suggested that it might represent a primitive form, placing it at the base of a branch of the phylogenetic tree leading to the Cyphophthalmi (mite-like harvestmen) and Palpatores (long-legged harvestmen). A number of online sources, such as Wikipedia, refer to Stygophalangium as being classified with the Eupnoi (a subgroup of the Palpatores), but this claim seems to be baseless. It seems to be derived from Joel Hallan's online list of harvestman species (which no longer appears to be available) but while Oudemans did compare Stygophalangium to the eupnoin Phalangium opilio (the common field harvestman) in his original description, he did not actually classify his new species with any particular subgroup of harvestmen. Eventually, Kury (2011) dismissed Stygophalangium from consideration in his summary of harvestman classification, stating that it 'is probably a member of the Acari'.

Unfortunately, as much as Stygophalangium might not be a convincing harvestman, it is also not a very convincing mite. One of the primary features that lead Oudemans to see Stygophalangium as a harvestman was its possession of three-segmented chelicerae. Most arachnids have chelicerae with only two segments (the basal segment and an opposing mobile claw or fang); three-segmented chelicerae are only found in two groups, the harvestmen and the mite group Parasitiformes. Of the four main groups (Opilioacarida, Holothyrida, ticks and Mesostigmata) within the Parasitiformes, none are similar to Stygophalangium. The ticks have distinctly modified (and kind of terrifying) blood-sucking mouthparts. The Holothyrida and Mesostigmata are both armoured to varying degrees, and mesostigs also bear a branched structure called the tritosternum underneath the mouthparts that is not described for Stygophalangium. The Opilioacarida are large, superficially harvestman-like mites that also have visible indications of external segmentation. And while there are a number of known lineages of aquatic mites, none of them really looks anything like Stygophalangium. It would be surprising if Oudemans, one of the leading mite researchers of his time, failed to recognise a mite when he had one in front of him! It is true that Oudemans' work underwent a precipitous decline in his last years as a result of problems with his mental health (Southcott 1961), but at the time of Stygophalangium's publication Oudemans remained alert and well.

Ventral view of Stygophalangium, with close-ups of chelicera, terminal pedipalp segments, and leg claw, from Oudemans (1933).

So if Stygophalangium was not a harvestman, and not a mite, then what was it? It is possible, of course, that it represented some taxon that has never been recorded since, but such an agnostic interpretation simply leaves the question of its affinities open. We can still at least try and compare it to other animals as best we can. One quite important point that I have avoided mentioning so far is that Oudemans' specimens were apparently not mature: Oudemans was unable to find indications of either a genital or anal opening. Though he described the body as unsegmented, it should be noted that his illustration is a reconstruction of what was apparently a not so smoothly mounted animal. Oudemans did note that a number of creases were visible on the bodies of his specimens, though he interpreted these as artefacts of slide-mountaing rather than segment boundaries because they did not appear to be placed evenly (with some creases even crossing over each other). Also, the supposed aquatic habitat may be a red herring. Subterranean samples are commonly collected by lowering sampling devices down a borehole, and it is not unknown for surface-dwelling organisms to fall in the borehole or be picked up when the traps are raised or lowered. So is Stygophalangium a larval harvestman or mite?

Again, we can rule out any arachnid except harvestmen or parasitiform mites due to the three-segmented chelicerae. The objections given above to adult ticks or Mesostigmata apply equally well to their juveniles, so they're also out. Larval Holothyrida lack the heavy armour of the adults, but these large litter-dwelling mites are not found anywhere near Europe. On the harvestman side of things, most harvestmen as both adults and nymphs have the second pair of legs particularly long and filamentous, functioning in a similar manner to the antennae of insects. The only harvestmen to lack this feature are the Cyphophthalmi, and together with the Opilioacarida they are the only real candidates for comparison with Stygophalangium. Both are soil-dwelling animals, and both are known from the Balkan region.

Larva of Opilioacarus texanus, from Klompen (2000).

One point in favour of an opilioacarid identity is that Oudemans described the chelicerae of Stygophalangium as inserted more dorsally than in other harvestmen. Opilioacarids have similarly inserted chelicerae, with a hypostome extending underneath the chelicerae. Oudemans also described Stygophalangium as lacking setae dorsally (instead having a somewhat scaly texture); opilioacarids have dorsal setae on the prosoma only. The opiliacarid prelarva (the earliest stage of its life cycle) has a scaly texture very similar to Stygophalangium (Klompen 2000), but mite larvae and prelarvae have only three pairs of legs. If Stygophalangium is an opilioacarid, it would have to be one of the later nymphal instars in which the fourth pair of legs has developed. Other features of opilioacarid juveniles conflict with Stygophalangium, such as the two pairs of large eyes on the opilioacarid prosoma. Also, Oudemans illustrated the venter of Stygophalangium with the coxae (the basalmost leg segment) integrated with the underside of the body, whereas opilioacarids (like other Parasitiformes) have the coxae free from the venter and attached by sockets. As Oudemans indicated the coxae of Stygophalangium with dotted lines only, it is possible that he inferred their position under the assumption of harvestman affinities. However, even if we assume this to be the case and that what Oudemans took to be the trochanters (the second leg segment) were actually the coxae, then Stygophalangium is left with one leg segment too few.

Larva of Siro rubens, from Juberthie (1964).

The only information on the juvenile stages of Cyphophthalmi is a brief description of the larva of Siro rubens by Juberthie (1964). Cyphophthalmi lack obvious eyes, and their legs do have the right number of segments for Stygophalangium. Juberthie described the cyphophthalmid larva as lacking a developed anus, which correlates with Oudeman's description of Stygophalangium (opilioacarid nymphs, in contrast, have a well-developed anal cone). He also recorded the presence of a pair of egg-teeth in the midline of the prosoma near the front of the body, in the same position where Oudemans described a distinctive pigmented spot on Stygophalangium. Points against a cyphophthalmid identification include the non-dorsal insertion of the chelicerae (though, again, one can't help wondering about the possibility of distortion through slide-mounting) and the presence of sparse but distinct dorsal setae. Especially difficult are the pairs of large setae marking the positions of the repugnatorial tubercles on either side of the prosoma. Unfortunately, Juberthie did not describe the venter of the cyphophthalmid larva, or comment on the degree of sclerotisation (mature cyphophthalmids are heavily sclerotised, whereas Stygophalangium is explicitly soft-bodied).

And that is about as far as we can go without looking at the original specimens. Personally, I suspect the issues with a cyphophthalmid identification are easier to overcome than those with an opilioacarid one (perhaps Oudemans did indeed mistake segment boundaries for mounting artefacts, and perhaps the dorsal setae had been lost post-mortem and Oudemans overlooked their sockets) but any such judgement requires the original description to be at least partially erroneous. Oudemans said that his type specimens were deposited in the Rijksmuseum van Natuurlijke Historie in Leiden; I wonder if they're still there?

REFERENCES

Juberthie, C. 1964. Recherches sur la biologie des opilions. Annales de Spéléologie 19 (1): 5–244.

Klompen, J. S. H. 2000. Prelarva and larva of Opilioacarus (Neocarus) texanus (Chamberlin and Mulaik) (Acari: Opilioacarida) with notes on the patterns of setae and lyrifissures. Journal of Natural History 34 (10): 1977–1992.

Oudemans, A. C. 1933. Ein neuer Stygobiont, Stygophalangium karamani Oudms. Zoologischer Anzeiger 103: 193–198.

Southcott, R. V. 1961. Studies on the systematics and biology of the Erythraeoidea (Acarina), with a critical revision of the genera and subfamilies. Australian Journal of Zoology 9: 367–610.

Hunter Balls: The Hydrachna Water-Mites

Hydrachna sp., copyright J. C. Schou.

Hydrachnae are among the most rapacious of living animals, bold, fierce and cruel, the natural and inveterate enemies of all their congenera; they are no less hostile to each other, against which is waged a permanent war of extermination. Neither do they hesitate in attacking such animals as are suitable to their appetites, though double the size of their assailant.

This lurid description was applied to the water-mites by John Graham Dalyell in his 1851 book, The Powers of the Creator displayed in the Creation, or observations on life amidst the various forms of the humbler tribes of animated nature. The water-mites are a diverse group found mostly in fresh waters around the world; Dalyell probably intended the name Hydrachna to cover all water-mites, but modern authors recognise a large number of genera and families in addition to Hydrachna (which is distinctive enough that it is placed in its own family. Whether Hydrachna proper deserves the full force of Dalyell's description may be debatable, but there is no denying that they are predators.

As explained in an earlier post, water-mites belong to a group of mites, variously referred as Parasitengonae, Parasitengonina or some variation thereof (depending where you look), that is characterised by a life cycle including parasitic larvae and predatory adults. In the case of Hydrachna, the adults, which are nearly spherical in shape and bright red in colouration, feed on the eggs of aquatic bugs such as water boatmen or backswimmers that they find attached to submerged plants (so for all his charcterisation of Hydrachna as 'bold, fierce and cruel', Dalyell probably committed no less horrific an act of cruelty to chickens when he sat down to a fried breakfast). Despite their aquatic habits, Hydrachna are only clumsy swimmers themselves. After all, it does not require any great athleticism to hunt down an egg.

Larvae of Hydrachna, copyright Pfliegler Walter.

As well as finding their food on submerged plants, female Hydrachna lay their own eggs in them. They have needle-like chelicerae that they use to cut into the plant's stem, and then lay their eggs in air spaces within the plant cells (up to 1500 at a time: Walter et al. 2009). When the eggs hatch, the emerging larvae (which are kind of rugby ball-shaped) swim in search of a suitable host. Usually, this is a water-bug of much the same sort whose eggs were being devoured by the larvae's parents, though some Hydrachna species have also been recorded parasitising aquatic beetles. While some water-mites are quite picky about where exactly they choose to attach to a host, Hydrachna are not so: they may attach pretty much anywhere. They also do not exclude each other: a single host insect may end up with a large number of Hydrachna larvae attached to it (enough to have a serious impact on the host's health). The palps on either side of the chelicerae are used to initially hold on to the host before the larva cuts into the host cuticle with its chelicerae; once its hold with the chelicerae is firm, the palps are folded out of the way (Redmond & Lanciani 1982). Once attached, feeding on the host's haemolymph may not commence immediately: if the larva has found itself on a host that has not yet reached maturity, it will often wait until after the host has moulted. This is because the feeding larva becomes massively engorged and may swell up to hundreds of times its original size. In this swollen state, it obviously becomes immobile (one cannot walk if one's legs no longer touch the ground); should the host shed its cuticle with the engorged larva attached, the larva would be unable to reattach itself to the host.

After about two weeks of feeding, the larva is ready to mature, but this does not necessarily mean leaving the host. In parasitengonines, the first nymphal instar (the protonymph) after the larval stage is dormant as the mite metamorphoses into something closer to its adult form, the first of the two 'pupal' stages that the mite will go through in its life (the second comes between the active deutonymphal instar and maturity, but involves less of a radical change in morphology). Hydrachna passes this 'pupal' stage while still attached to the host, only detaching when it becomes an active deutonymph. As well as saving the larva the inconvenience (and danger) of dropping off the host while in an engorged state, this helps ensure that the deutonymph emerges in a suitable habitat. Hydrachna prefers still waters, such as ponds and lakes. Some species of Hydrachna prefer to breed in temporary seasonal pools, and may remain attached to the host for several months while their home pools are dry. Somehow they can tell the difference between the temporary pools and the more permanent waters in which the hosts spend the rest of their time.

REFERENCES

Redmond, B. L., & C. A. Lanciani. 1982. Attachment and engorgement of a water mite, Hydrachna virella (Acari: Parasitengona), parasitic on Buenoa scimitra (Hemiptera: Notonectidae). Transactions of the American Microscopical Society 101 (4): 388-394.

Smith, I. M., D. R. Cook & B. P. Smith. 2010. Water mites (Hydrachnidiae) and other arachnids. In: Thorp, J. T., & A. P. Covich (eds) Ecology and Classification of North American Freshwater Invertebrates, pp. 485-586. Academic Press.

Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology, 3rd ed., pp. 233-420. Texas Tech University Press.

The Eater of Light

The Waitomo harvestman Forsteropsalis photophaga, from Taylor & Probert (2014).

A little less than a year ago, I was contacted by a student at the University of Auckland in New Zealand, asking me about some harvestmen that she'd been trying to identify me from the Waitomo cave system. This incited a certain degree of excitement on my part, because I was not entirely unfamiliar with Waitomo's harvestmen. I had first seen specimens from there while doing my MSc back in 2001 or 2002, and had realised then that they represented an undescribed species. However, for various reasons, I had not yet published a description of the species in question. So when Anna contacted me, I decided it was time to bump the Waitomo harvestmen up the to-do list, and I replied to her asking if she would be interested in collaborating on a paper on the Waitomo harvestmen. She agreed, and the resulting paper came out just last week: C. K. Taylor & A. Probert, "Two new species of harvestmen (Opiliones, Eupnoi, Neopilionidae) from Waitomo, New Zealand".

Image of Waitomo cave, from here.

The Waitomo caves may be the world's only tourist attraction centred around an infestation of flies. The caves are home to an abundant population of glow-worms, larvae of the fungus gnat Arachnocampa luminosa. These fly larvae live on the roof of the cave, held in place by a silken hammock, and produce spots of brilliant blue light. It is the spectacle of these lights that draw the tourists, but for the glow-worms they serve a different purpose: the lights attract insects flying in the cave. In flying towards the light, insects become entangled in sticky threads that each glow-worm suspends below its hammock, providing the glow-worm with food. You can see a video of the process here, taken from the BBC's Planet Earth series.

But the glow-worms are not without predators of their own. With their long slender legs, harvestmen are able to carefully tip-toe between the sticky threads and pluck out the glow-worms, as from a luminous buffet (they also eat them at the pupal and adult stages). The harvestmen of Waitomo were studied by Myer-Rochow & Liddle (1988), who identified two species. One, a 'short-legged harvestman' Hendea myersi cavernicola (which actually has decidedly long legs, natch), is endemic to the cave system and was identified by Meyer-Rochow and Liddle as a strict troglobite (i.e. it spends its entire life within the cave). It has a number of features commonly associated with cave-dwelling, such as pale coloration and lengthened legs. It does differ from most troglobites in that it is not blind: while its eyesight is dim, it does retain enough to find its glowing prey.

Meyer-Rochow and Liddle also identified a 'long-legged harvestman' in the Waitomo caves, which they referred to as 'Megalopsalis tumida'. This name refers to a species first described from Wellington, quite some distance to the south, that now goes by the name of Forsteropsalis fabulosa (and has made an earlier appearance at this site, where it was the subject of this post). As it turns out, I identified two species of Forsteropsalis in material from the caves, neither of which was F. fabulosa. I can't be certain which was the species being looked at by Meyer-Rochow and Liddle. For various reasons, I suspect that they may have been looking at examples of both, but, as I've never been able to locate any vouchers for their study, I can't really say (remember, kids, vouchers are important).

Forsteropsalis bona, from Taylor & Probert (2014).

One of these species is indeed very similar to Forsteropsalis fabulosa, and has accordingly been labelled Forsteropsalis bona. Indeed, the two species are similar enough that I can now see that the photograph I used in my earlier post to illustrate F. fabulosa in fact shows an individual of F. bona. The primary difference between the two is in their pedipalps: in F. fabulosa, the patella of the pedipalp has a distinct finger-like process that is much reduced in F. bona. Forsteropsalis bona is not a strict troglobite: specimens have been collected at Waitomo both inside and outside the cave entrance. Instead, it is what is called a troglophile: individuals of F. bona probably use the caves as a cool, damp place to hang out during the day, emerging to forage outside the cave at night. This is the same pattern of behaviour found in New Zealand's cave wetas.

The second species is the beauty pictured at the top of this post. Its species name, photophaga, means 'eater of light', referring of course to its probable predation on glow-worms. This is a stunning animal: the enormous chelicerae typical of New Zealand Neopilionidae are rendered even more eye-catching by the presence of rows of longer spines (offhand, we don't yet know what the females of either of the Waitomo species look like, but they probably resemble other Forsteropsalis females in lacking the long chelicerae of the males). Whether Forsteropsalis photophaga is a troglobite or a troglophile is a bit more uncertain. I'm not aware of it having ever been collected outside the caves, but it doesn't seem to have the obvious modifications for cave-dwelling of Hendea myersi cavernicola (though when t comes to assessing elongated limbs in what is already a long-legged harvestman... how are you going to tell?). At present, I'm guessing troglophile rather than troglobite, but future studies may easily prove me wrong.

Forsteropsalis photophaga is also an intriguing animal from a taxonomic viewpoint. In the past, the two New Zealand harvestman genera Pantopsalis and Forsteropsalis have been pretty easy to distinguish, but F. photophaga has some features that are more reminiscent of Pantopsalis than of Forsteropsalis. Recently, other things have been brought to my attention that suggest that, while Pantopsalis as we currently know it still seems fairly robust, Forsteropsalis is beginning to look decidedly fuzzy around the edges. The relationship between these two genera (if, indeed, they should still be recognised as two separate genera) has still not been resolutely ironed out.

REFERENCE

Meyer-Rochow, V. B., & A. R. Liddle. 1988. Structure and function of the eyes of two species of opilionid from New Zealand glow-worm caves (Megalopsalis tumida: Palpatores, and Hendea myersi cavernicola: Laniatores). Proceedings of the Royal Society of London Series B (Biological Sciences) 233: 293–319.

The World's Scorpion

Pair of lesser brown scorpions Isometrus maculatus in captivity, from here. The more elongate individual at lower left is a male; his stouter companion is female.

With their elongate, sting-tipped tails, scorpions are instantly distinguishable from any other arachnid. Depending on how you look at it, they are either charismatic or infamous (not many invertebrates have constellations named after them). Yet though the world diversity of scorpions is not unrespectable (about 1750 species have been described so far), distinguishing one scorpion species from another can be a challenging prospect. They tend, as a whole, to be a morphologically conservative group.

As a result, new species of scorpion continue to be described, at a rate limited only by the relatively small number of people taking up the challenge. Isometrus is a genus of about thirty species of scorpion found mostly from in southern Asia and Australasia, from Pakistan to northern Australia and New Caledonia. A good third of those species have only been described since 2000, and probably more remain to be described. They are small, relatively slender scorpions, often with the 'fingers' of the chelae noticeably darker than the 'palms' (as in the photo above). They have a sting that has been referred to as painful, but doesn't seem to have lead to recorded fatalities in humans.

Isometrus has been divided between two subgenera, Isometrus sensu stricto and Reddyanus (Kovařík 2003). The two subgenera are distinguished primarily by the locations of trichobothria, long sensory hairs, on the chelae. The higher diversity of species belong to Reddyanus, but Isometrus is by far the more widespread subgenus. This is due to its inclusion of one particular species: I. maculatus, commonly given the rather underwhelming name of 'lesser brown scorpion'. For some reason, Isometrus maculatus has proven itself very amenable to transport by humans. It may have been originally native to Sri Lanka (as cited here) but from there it has spread to tropical regions around the world. It is found in North America, South America, Africa and Australia, and on various oceanic islands such as Hawaii, Saint Helena and the Seychelles. In Europe, it is only known from southern Spain, though it may have been the species originally indicated by Linnaeus' 'Scorpio europaeus' (Fet et al. 2002; some authors have consequently used the name 'Isometrus europaeus' for this species, but Linnaeus' name was declared invalid by the ICZN due to the uncertainty of its identity). Currently, I. maculatus is regarded as the world's most widespread scorpion species. No other Isometrus species has been subject to the same degree of spread, though I am personally inclined to wonder about the distribution of I. heimi, recorded by Kovařík (2003) from both New Guinea and New Caledonia.

REFERENCES

Fet, V., M. E. Braunwalder & H. D. Cameron. 2002. Scorpions (Arachnida, Scorpiones) described by Linnaeus. Bull. Br. Arachnol. Soc. 12 (4): 176-182.

Kovařík, F. 2003. A review of the genus Isometrus Ehrenberg, 1828 (Scorpiones: Buthidae) with descriptions of four new species from Asia and Australia. Euscorpius 10: 1-19.

There's No Such Thing as Caddids

Caddo agilis, from here.

Long-time readers of this site may recall my previous rants on the subject of the prolific, but not entirely reliable, arachnologist Carl-Friedrich Roewer. Hopefully, this post will serve to rehabilitate Roewer's image a little, because occasionally something comes along about which he was right in the first place.

Among Roewer's innovations in Die Weberknechte der Erde, his 1923 revision of the world Opiliones fauna, was the introduction of a new family for Acropsopilio, an odd little harvestman from South America. He placed this new family in the Dyspnoi, a subgroup of the Palpatores (long-legged harvestmen) that is otherwise found in Eurasia and North America. Acropsopilio was a distinctive beast, a tiny harvestman with relatively massive eyes (just take a look at the picture below!) Over time, other authors added to the Acropsopilionidae: species are now known from Australia, New Zealand and South Africa. They are nowhere comon, though.

Specimen of Acropsopilio neozelandiae, photographed by Stephen Thorpe.

In 1975, the acropsopilionids were revised by Shear (1975), who proposed that they were related to Caddo, a genus of harvestmen found in north-eastern Asian and north-eastern North America. That's not a typo, by the way: the range of this genus includes Japan and New England, but not the spaces in between. To make things just that extra bit wierder, the genus includes two species, C. agilis and C. pepperella, both of which are found in both the sections of its overall range. Genetic analysis has demonstrated that this wierdness is real, and not just convergence or one variable species (Shultz & Regier 2009). Caddo had previously been classed as a member of the Eupnoi, the other main subgroup within the Palpatores, but resembled acropsopilionids in features such as the small size and large eyemound. Shear proposed classing them all as a single family, Caddidae, with two subfamilies: one for Caddo and one for the Acropsopilioninae. Subsequent authors have followed his lead, and the Caddidae has come to be placed within the Eupnoi as the sister taxon to the Phalangioidea (the group including the familiar long-legged harvestmen such as the field harvestman Phalangium opilio).

Nevertheless, there was still a bit of humming and hawing going on behind the scenes. Despite the overall similarities in habitus between Caddo and acropsopilionines, several of the finer details (such as the structure of the pedipalps and genitalia) were quite different. Phylogenetic studies commenting on the position of caddoids within the Opiliones had generally included Caddo only, and not included any representatives of the acropsopilionines. And so it is quite welcome to see a new publication by Groh & Giribet (in press) in which they produced a molecular phylogenetic analysis of the caddids as a whole. The result, as hinted in the first paragraph, is that the caddids are not supported as a monophyletic group. Caddo remains in its accustomed position within the Eupnoi, but the acropsopilionids are placed as the sister clade to the Dyspnoi. Roewer, it turns out, had them in the right place to begin with.

This has some interesting implications: for instance, the otherwise entirely Holarctic Dyspnoi have just acquired a Gondwanan basal group. Also, the large eyemound is either a convergent feature between Caddo and acropsopilionines, or a retained primitive feature from the palpatorean common ancestor. Groh & Giribet suggest the latter, but I suspect the former to be just as likely (it may be related to small size: some phalangioids, such as the Mediterranean Platybuninae and the Western Australian Megalopsalis tanisphyros, also have large-ish eyemounds). But the greatest surprise for yours truly was something else: one particular 'acropsopilionine' genus, Hesperopilio, was not placed either with Caddo or the other acropsopilionines. Instead, it was placed closer to the the phalangioid family Neopilionidae: the subject of my own research.

When I produced my revision of the Australasian phalangioid family Monoscutidae (which I ended up synonymising with Neopilionidae), I included Caddo as an outgroup taxon in my morphological phylogenetic analysis. At the time, my supervisor asked me why I didn't include an acropsopilionine as well, but I demurred on two points. One was that, as rare as acropsopilionines were in collections, males were even rarer (there is evidence that they are commonly parthenogenetic, as for that matter is Caddo). The other was that acropsopilionine genitalia were truly bizarre, and I couldn't determine which parts of the acropsopilionine penis corresponded to where on the monoscutid organ.

I was basing that judgment on Acropsopilio and the South African genus Caddella (offhand, there is a longstanding tradition in harvestman taxonomy that whenever the name Caddella appears in a paper, it must be mis-spelled at least once). I still stand by that judgment. But upon seeing the results of Groh and Giribet's molecular analysis, I looked up the description of Hesperopilio (Shear 1996), which includes a drawing of the male genitalia. And suddenly, I was struck by the possibility that they could indeed be neopilionid-like. So I tried entering Hesperopilio into my original data set using the published descriptions. The result? Though missing a fair amount of data (my coding would need to be checked against actual specimens), a rough run suggests that morphology supports Hesperopilio as a neopilionid too!

The simplified version of what I end up with. Remember, this is by no means a thoroughly vetted result; this is just me going "what if I do this?"

So let that be a lesson, I suppose. Because of the belief that Hesperopilio was an acropsopilionine, I had never even considered taking a closer look at it. As it turns out, I really should have!

REFERENCES

Groh, S., & G. Giribet (in press) Polyphyly of Caddoidea, reinstatement of the family Acropsopilionidae in Dyspnoi, and a revised classification system of Palpatores (Arachnida, Opiliones). Cladistics.

Shear, W. A. 1975. The opilionid family Caddidae in North America, with notes on species from other regions (Opiliones, Palpatores, Caddoidea). Journal of Arachnology 2: 65–88.

Shear, W.A. 1996. Hesperopilio mainae, a new genus and species of harvestman from Western Australia (Opiliones: Caddidae: Acropsopilioninae). Records of the Western Australian Museum 17: 455–460.

Shultz, J. W., & J. C. Regier. 2009. Caddo agilis and C. pepperella (Opiliones, Caddidae) diverged phylogenetically before acquiring their disjunct, sympatric distributions in Japan and North America. Journal of Arachnology 37: 238–240.

Bye, Bye, Spinicrus

Female Spinicrus...no, sorry, Megalopsalis nigricans, photographed by Tony.

I've just had a paper out. The funny thing is, it's making me feel both pleased yet a little maudlin, because it represents something of an end of an era. The last part of my PhD thesis has been published. The last remnant of my student days has been cast off. I think I need a hug.

The paper in question is: Taylor, C. K. 2013. Further revision of the genus Megalopsalis (Opiliones, Neopilionidae), with the description of seven new species. ZooKeys 328: 59-117. It's open access, so go take a squizz. One thing that I also can't resist pointing out, though I don't know if it really makes much difference because it's a primarily online journal and hardly anyone will see the print issue: it's one of my images on the cover.

Technically, this paper represents my long-awaited (by me, at least) revision of the harvestman genus Spinicrus. In the end, though, I had to change the title of the paper, because on of the main results of this revision was that Spinicrus became a synonym of the older genus Megalopsalis. In an earlier publication, I cut Megalopsalis down to size by removing its New Zealand species to a new genus, Forsteropsalis. But now it's back, and stronger than ever before!

Female Megalopsalis tasmanica, the erstwhile Spinicrus tasmanicum. Another photograph from Tony.

Previously, Spinicrus was primarily separated from Megalopsalis by one feature: the presence of a side branch on one of the segments of the pedipalps of Megalopsalis. Taxonomists tend to be wary of defining a group purely by the absence of features. It implies that the members of that group are united more by the idea that they just don't belong in any other group, rather than anything that actually connects them per se. So, in this case, Megalopsalis was the species with a pedipalp side-branch, and Spinicrus was... the rest. It also didn't help matters that a pedipalp side-branch is something that has evolved and de-evolved a number of times within harvestmen, leading to a bit of questioning about its significance. A few years ago, I separated a few of the more distinctive 'Spinicrus' as the genus Neopantopsalis. This made Spinicrus a bit less heterogeneous but still didn't solve the underlying issue. It just meant that now you took out Megalopsalis and took out Neopantopsalis, and Spinicrus was still... the rest.

The answer, as so often in invertebrate taxonomy, came largely from the boy bits. When I looked at the male genitalia, I found that Megalopsalis and Spinicrus species shared a similar penis morphology, in which the end of the penis was fairly short, flat and shaped more or less like a rounded triangle:

This is what a 'Spinicrus' stewarti penis looks like.
In contrast, the end of the penis in Neopantopsalis species is longer, as demonstrated by N. thaumatopoios:

Put these features into a phylogeny of the family that these genera belong to (Neopilionidae), and I overall ended up with this:

Consensus of various phylogenetic analyses under various parameters (numbers at nodes represent the percentage of analyses in which that clade was recovered). Taxa coloured green are what would have been called 'Spinicrus' previously, while those in red would have been 'Megalopsalis'.

Note that this is a bit of a faux phylogeny, because it's a comparative summary of separate analyses under separate parameters (see the paper for details). Only those clades marked with a 100 were supported in all analyses. The important detail is the distribution of the green 'Spinicrus' relative to the red 'Megalopsalis': no matter what the analytical conditions, 'Megalopsalis' was always nested well within 'Spinicrus'. Indeed, under most conditions, 'Megalopsalis' was polyphyletic within 'Spinicrus'. Because of this, and because of the lack of any positive uniting features for Spinicrus species that were not also present in Megalopsalis, I felt the best course of action was to declare the two genera synonyms. Also subsumed under Megalopsalis was Hypomegalopsalis, a species that I had earlier established for a single species of uncertain affinities (Megalopsalis tanisphyros in the tree above). At the time, I commented that, "if anyone conducts a further study in the future that supports quashing Hypomegalopsalis, I won't be protesting". The fact that I got to do that myself just makes me all the happier.

There's a lot more I could talk about here, but I'm sure you all stopped reading long ago. Just go to the paper.