Platybunus: the Wide-Eyed Harvestmen of Europe

The western Palaearctic region (that is, Europe and the immediately adjacent parts of Asia and northern Africa) is home to a diverse and distinctive fauna of harvestmen. Among the various genera unique to this part of the world are the forest- and mountain-dwellers of the genus Platybunus.

Platybunus pinetorum, copyright Donald Hobern.

Platybunus species are moderate-sized long-legged harvestmen of the family Phalangiidae, the central body in larger individuals being about eight millimetres long (Martens 1978). Their most characteristic feature is a relatively large eye-mound, distinctly wider than long and occupying a large section of the anterior carapace. As with other European phalangiids, they eye-mound is ornamented with a row of denticles each side though the body lacks denticles over the remainder of the dorsum. The body is often comparatively slender, tapering towards the rear (particularly in males), and is marked on the dorsum by a darker median band. The pedipalps have a pair of well-developed setose apophyses on the inner distal ends of the patella and tibia, and a series of long spine-like tubercles on the underside of the femur. These tubercles presumably function in the capture of prey, forming a basket that can be closed around the harvestman's victims. External sexual dimorphism in Platybunus is fairly minimal though females are overall larger and fatter. The penis is notably long and slender with a relatively small glans, offset from the shaft by a more or less marked constriction.

Platybunus bucephalus, copyright Adrian Tync.

Martens (1978) recognises four species of Platybunus found in higher altitude regions of central Europe with the species P. bucephalus and P. pinetorum occupying much of the genus' range. Platybunus bucephalus may be distinguished from P. pinetorum by, among other features, its relatively shorter legs. Platybunus pallidus is endemic to the Carpathians, and the tiny P. alpinorelictus inhabits the Garda Mountains of northern Italy. Another species, P. anatolicus, was described from Turkey by Roewer (1956)*. In general, Platybunus species inhabit alpine and subalpine forests, being found among the herbaceous undergrowth, under bark or on rock faces. Where their ranges overlap, P. bucephalus is more accustomed to extending beyond the forest margins than P. pinetorum and may be found above the tree-line. In recent years, the range of P. pinetorum has extended northwards, being first recorded from the UK in 2010 and Sweden in 2015 (Fritzén et al. 2015). At least some populations of P. pinetorum are capable of reproducing parthenogenetically and this may have played a part in its spread.

*Platybunus mirus was described by Loman (1892) on the basis of two male specimens that supposedly came from Sumatra. Though the identity of this species has never been resolved (Loman's illustration of the penis is at least suggestive of a true Platybunus), the claimed locality seems almost certain to be an error of some kind.

The internal classification of the Phalangiidae remains in need of further investigation. Platybunus has been recognised by some authors as forming a subfamily Platybuninae with a cluster of other western Palaearctic genera bearing similar ventrally spined pedipalps (Zhang & Zhang 2012). However, other authors have not separated this group from the subfamily Phalangiinae. The platybunines may represent a phylogenetically coherent grouping, or their shared features may reflect adaptations to a similar life style. The genital morphology of Platybunus is recognisably distinct from that of other platybunines which may argue against any relationship (Martens 1978). On the other hand, platybunines might possibly be distinguished from phalangiines by the chemical composition of their repugnatorial gland secretions (Raspotnig et al. 2015). A formal analysis of the family's evolution would be a welcome advance.

REFERENCES

Fritzén, N. R., V. Rinne, M. Sunhede, A. Uddström, S. Van de Poel & P. De Smedt. 2015. Platybunus pinetorum (Arachnida, Opiliones) new to Sweden. Memoranda Soc. Fauna Flora Fennica 91: 37–40.

Loman, J. C. C. 1892. Opilioniden von Sumatra, Java und Flores. In: M. Weber (ed.) Zoologische Ergebnisse einer Reise in Niederländisch Ost-Indien vol. 3 pp. 1–26, pl. 1. E. J. Brill: Leiden.

Martens, J. 1978. Spinnentiere, Arachnida: Weberknechte, Opiliones. Gustav Fischer Verlag: Jena.

Raspotnig, G., M. Schaider, P. Föttinger, V. Leutgeb & C. Komposch. 2015. Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis. Chemoecology 25: 63–72.

Roewer, C. F. 1956. Über Phalangiinae (Phalangiidae, Opiliones Palpatores). (Weitere Weberknechte XIX). Senckenbergiana Biologica 37 (3–4): 247–318.

Zhang, C., & F. Zhang. 2012. On the subfamilial assignment of Platybunoides (Opiliones: Eupnoi: Phalangiidae), with the description of a new species from China. Zootaxa 3190: 47–55.

Pied Harvestmen of the Antilles

Harvestmen of the Neotropical family Cosmetidae have been featured on this site a couple of times before. Each time, I've commented on the dire taxonomic state of this diverse family, with many genera being poorly or inaccurately defined. Thanks to extensive (and continuing) studies in recent years by Braxilian researchers and their associates, this situation has been progressively improving, but we still have a lot to learn.

Cynortoides sp., copyright Damion Laren Whyte.

Cynortoides is a genus currently holding ten species of cosmetid. Most of these are found on the islands of the Greater Antilles—Cuba, Jamaica and Hispaniola—though the genus has also been recorded from adjoining regions of Mexico and Venezuela (Kury 2003). As with other cosmetids, Cynortoides has historically been defined largely be features of the external spination, including a lack of spines on the legs, two pairs of spines in the rear part of the dorsal scutum, and no spines on the free abdominal segments (Mello-Leitão 1933). Also as with other cosmetid genera, Cynortoides species are colourfully patterned. The name of one species, C. v-album, refers to its characteristic bright white V marking on the back (though personally, I would describe the pattern as more of a Y).

Though this genus does not yet appear to have been revised in detail, some of its species were included in a recent broader study of cosmetid phylogeny by Medrano et al. (2021). They found strong support for an association between the Cuban C. cubanus and the Hispaniolan C. v-album, together with two other Cuban species previously included in the related genus Cynorta. These last two species were consequently transferred to Cynortoides though Medrano et al. did not comment on whether this affected the genus' established diagnosis. The authors speculated that further studies might prove Cynortoides to be a strictly Greater Antillean genus with mainland records being misplaced. Cynortoides would not be unique in this regard: the islands of the Caribbean are home to a number of lineages found nowhere else, reflecting a long history independent of the adjoining continents.

REFERENCES

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1–337.

Medrano, M., A. B. Kury & A. C. Mendes. In press 2021. Morphology-based cladistics splinters the century-old dichotomy of the pied harvestmen (Arachnida: Gonyleptoidea: Cosmetidae). Zoological Journal of the Linnean Society.

Mello-Leitão, C. F. de. 1933. Notas sobre os opiliões do Brasil. Descritos na obra postuma de Sörensen: "Descriptiones Laniatorum". Boletim do Museu Nacional 9 (1): 99–114.

Pseudogagrella: A Harvestman Torn

The Sclerosomatidae are one of the most diverse of the currently recognised harvestmen families, and one of the most problematic when it comes to classification. In various earlier posts, I have noted the challenges that bedevil sclerosomatid systematics, many reflecting a historical focus on superficial external features of questionable evolutionary significance. Perhaps no taxon more neatly exemplifies the problems with higher sclerosomatid classification than the eastern Asian genus Pseudogagrella.

Pseudogagrella sakishimensis, copyright Tomoya Suzuki.

Historically, the greater number of sclerosomatids have been divided between two major subfamilies, the Leiobuninae and Gagrellinae. The Leiobuninae have mostly been recognised as living in the northern temperate regions whereas the Gagrellinae were mostly tropical. The division between the two subfamilies has long been regarded as more than a little fuzzy, and has usually hinged on a single feature: the presence (Gagrellinae) or absence (Leiobuninae) of rings of flexible integument (noduli) in the femora of the legs. Pseudogagrella is a genus of sclerosomatid harvestmen recognised from Japan, Taiwan, China and Sumatra (Chen & Shih 2017). Members of this genus lack leg noduli so have historically been included in the Leiobuninae. The problem is that their overall appearance, with a tendency to bold coloration, a tall median spine rising from the hardened scute covering most of the abdomen, and legs that are not merely long but ludicrously so (even by harvestman standards), is extremely similar to species of Gagrellinae. So much so, in fact, that some species currently placed in Pseudogagrella were long included in the archetypical gagrelline genus, Gagrella (Suzuki 1977).

With the distinction between the two subfamilies being so vague, I don't think it really came as that much surprise to anyone when molecular phylogenetics underlined the need for a thorough re-working of sclerosomatid systematics. Though the analysis conducted by Hedin et al. (2012) did not support the prior distinction between 'leiobunines' and 'gagrellines', it did suggest the existence of distinct lineages occupying distinct geographical regions. One species of Pseudogagrella included in the analysis (the southern Japanese P. amamiana) was placed in a cluster of eastern Asian species including other Asian 'gagrellines', but also the 'leiobunine' 'Leiobunum' japonicum. So it seems likely that, should subfamilies of Sclerosomatidae continue to be recognised, Pseudogagrella will indeed be a member of Gagrellinae, but Gagrellinae itself shall not quite be what people think of it as being.

Pseudogagrella dorsomaculata, copyright Tyus Ma.

There is also, of course, the question of whether Pseudogagrella itself is a coherent unit. Hedin et al. (2012) included only the one Pseudogagrella species in their analysis and the need for an extensive revision of the Asian sclerosomatid genera still remains. A study of Chinese species assigned to the genus Melanopa (Zhang & Zhang 2013), which is primarily distinguished from Gagrella by having relatively shorter legs, suggested the possibility of this 'genus' being divided between groups of Palaearctic and Indo-Malayan species, and I've wondered if this division might carry further (unfortunately, I'm not aware of any Indo-Malayan 'gagrellines' being included in molecular phylogenies; I think all the Asian species covered by Hedin et al. were Palaearctic). The majority of Pseudogagrella species, found in Japan and Taiwan, can be comfortably compared to other sclerosomatids from that region, but the Sumatran P. multimaculata, and possibly the southern Chinese species, might turn out to be closer to their own geographical peers. As always, a great deal of research remains to be done.

REFERENCES

Chen, S.-L., & H.-T. Shih. 2017. Descriptions of three new species of the harvestmen genus Pseudogagrella (Opiliones: Sclerosomatidae: Gagrellinae) from Taiwan, supported by morphological and molecular evidence. Zootaxa 4268 (1): 34–52.

Hedin, M., N. Tsurusaki, R. Macías-Ordóñez & J. W. Shultz. 2012. Molecular systematics of sclerosomatid harvestmen (Opiliones, Phalangioidea, Sclerosomatidae): geography is better than taxonomy in predicting phylogeny. Molecular Phylogenetics and Evolution 62 (1): 224–236.

Suzuki, S. 1977. Opiliones from Taiwan (Arachnida). Journal of Science of the Hiroshima University, Series B, Division 1 (Zoology) 27 (1): 121–157.

Zhang, C., & F. Zhang. 2013. Notes on some species of the genus Melanopa (Opiliones: Sclerosomatidae: Gagrellinae) from China, with description of a new species. Journal of Arachnology 41: 306–318.

Metavononoides: Retreating from the Coast

I've commented before on the taxonomic issues bedevilling the study of South American harvestmen, particularly members of the diverse family Cosmetidae. Recent years have seen researchers make gradual but steady progress towards untangling these multifarious snarls by more firmly establishing the identities of this family's many genera.

Metavononoides guttulosus photographed by P. H. Martins, from Kury & Medrano (2018).

The genus Metavononoides was established by Roewer in 1928 for two species from south-eastern Brazil. As with other Roewerian genera, its definition was not exactly robust, being based on a combination of tarsal segment count together with the presence of a pair of large spines on the dorsal scutum. The genus was later re-defined by Kury (2003) who used it for a group of species found in the Brazilian Atlantic Forest region around Rio de Janeiro. Members of this group shared a number of distinctive features including the presence of a distinctive U-shaped marking (later dubbed a 'lyre mask' or 'lyra')on the scutum. A number of species previously placed in other genera were transferred to Metavononoides, and the next few years saw the description of a couple more species in the genus. And then Paecilaema happened.

The genus Paecilaema was first established by C. L. Koch in 1839 but a poor description of its type species P. u-flavum lead to confusion about its identity. Over time, Paecilaema became associated with a large number of species over a range stretching from Mexico to Brazil (as an aside, it doesn't help matters that Paecilaema has been one of those names that taxonomists have found themselves chronically uncertain how to spell). When Kury & Medrano (2018) recently set out to determine the exact identity of Paecilaema by determining that of its type, they fixed P. u-flavum as a species that was common around Rio de Janeiro and that corresponded to one of the species included by Kury (2003) in Metavononoides. As a result, many of the species shifted by Kury (2003) into Metavononoides were shifted once again into Paecilaema. Many of the species assigned to Paecilaema from outside the Atlantic Forest Region remain unrevised but will almost certainly prove to require re-classification.

Metavononoides barbacenensis photographed by P. H. Martins, from Kury & Medrano (2018).

Metavononoides was not outright synonymised with Paecilaema, though. Among the group of species possessing the aforementioned lyra on the scutum, Kury & Medrano (2018) identified two distinct subgroups. In one, corresponding to Paecilaema, the lyra is made up of two components. Part of the lyra is composed of light coloration on the plane of the scutum itself while another part is raised granules. In some species, these granules are particularly concentrated along the margins of the lyra (you can see an example on this on Flickr, photographed by Mario Jorge Martins; though labelled Metavononoides, this individual is now identifiable as Paecilaema u-flavum). In the second subgroup, corresponding to Metavononoides, the differentiated coloration on the plane of the scutum is absent and the lyra is composed solely of raised granules. Not only are the two genera morphologically distinct, they are also more or less geographically distinct. Whereas Paecilaema is found in the moist broadleaf forests closer to the coast, Metavononoides is now restricted to species largely found in the grasslands and shrublands further inland, corresponding to the Cerrado region. Though more depauperate of species than it was before, the identity of Metavononoides is certainly firmer.

REFERENCES

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1–337.

Kury, A. B., & M. Medrano. 2018. A whiter shade of pale: anchoring the name Paecilaema C. L. Koch, 1839 onto a neotype (Opiliones, Cosmetidae). Zootaxa 4521 (2): 191–219.

Roewer, C. F. 1928. Weitere Weberknechte II. II. Ergänzung der: "Weberknechte der Erde", 1923. Abhandlungen der Naturwissenschaftlichen Verein zu Bremen 26 (3): 527–632, 1 pl.

Rhampsinitus Re-Redux

I've featured the African harvestman genus Rhampsinitus on this site twice before, but I'm going to have another dive into it today. There's still more I can say about this remarkable genus.

Male Rhampsinitus, possibly R. leighi, copyright Peter Vos. The individual ahead of the male is another Rhampsinitus, probably a female; there's also a short-legged harvestmen beneath the male.

There's more I could say about African phalangiids in general, in fact. There's never been a proper phylogenetic study of the long-legged harvestman family Phalangiidae, so we can't speak with confidence about the relationships between the African members of this group and their relatives elsewhere, but it would not be unexpected if the sub-Saharan phalangiids form an evolutionarily coherent group. Many of the family's most striking exemplars are to be found on the African continent: Cristina with their thick, spiky front legs; sleek, flattened Odontobunus, Guruia with their chelicerae like a pair of jar tongs held in a boxing glove. Rhampsinitus' current position as the best-known African harvestman genus is probably due not only to its diversity but also to its more temperate centre of distribution placing it closer to researchers than these other more equatorial genera.

As mentioned in my first post on the genus, there are currently over forty recognised species of Rhampsinitus. As alluded to in my second post, that number might be expected to change in the future. No reliable identification key is currently available for Rhampsinitus, nor is the information available for many species that would allow such a key to be written. A key to the southern African species was provided by Kauri (1961) but, while I did find this key invaluable when I conducted my own tentative foray into rhampsinitology, I couldn't recommend it to a novice. Kauri was simply unaware of the extreme variation that can be found among male Rhampsinitus belonging to a single species. There are only a handful of species for which both major and minor males have been described and, as I explained previously, minor males may not be identifiable to species without examining genitalia.

Probably a male Rhampsinitus vittatus, copyright Nanna.

This, obviously, is a problem for the handful of species that have been described from what appear to be minor males. Some of these, such as Rhampsinitus fissidens and R. hewittius, are probably doomed to remain mysteries at least until someone redescribes their types. Others may be more recognisable. Rhampsinitus qachasneki is an unusually spiny species described from the mountains of Lesotho, with some of the denticles along the front edge of the body multi-pointed. These distinctive denticles, like repurposed muntjak antlers, might reasonably be expected to be present in any major males of this species, if they exist. The challenge may be even greater for the handle of species that have been described from females. Nevertheless, the known female of R. maculatus, another Lesotho mountain species, has a distinctive spotted colour pattern and thick, remarkably hairy pedipalps that might be expected to show their analogues in the unknown males (again, if they exist: we're kind of glossing over the point that some harvestmen species are known to be parthenogenetic, because harvestmen systematics is so heavily predicated on male genital morphology that the idea of an all-female harvestman species is a trifle intimidating*).

*I assume that this is precisely what Zappa had in mind when he got to the end of Thing-Fish.

Then, of course, there's the persistent question of Rhampsinitus lalandei. This was the first species included in Rhampsinitus in 1879 and as such represents the type or sine qua non of the genus. As was not unusual for the time, its author Eugene Simon was a bit vague about where his original specimen(s) had come from, giving the locality as simply 'Cafrerie'. Cafrerie, rendered in English as Kaffraria or Kaffirland, is a geographical designation that has fallen out of favour these days for reasons I would hope to be obvious, but was commonly used during the 1800s to refer to the area around the eastern coast of modern South Africa, particularly around Port Elizabeth. Unfortunately, Simon's description of R. lalandei is not definitive by modern standards—most of the features described could apply to any number of Rhampsinitus species—and Simon's original specimen appears to have been lost. This presents a problem for any who would suggest that this large genus should be divided up as it might become uncertain which division represents the true Rhampsinitus. Starega (2009) suggested that R. lalandei might be the same as R. crassus, a species definitely found in the Port Elizabeth region. However, it should be noted that Simon described R. lalandei as being irregularly armed with denticles dorsally. In the majority of Rhampsinitus species, the denticles on the opisthosoma form very neat transverse rows, but in others they are a bit more messily placed. Rhampsinitus crassus is one of the former species but the description of R. lalandei suggests it may have been one of the latter. So if anyone's looking at harvestmen from around that area, keep your eyes open.

REFERENCES

Kauri, H. 1961. Opiliones. In: Hanström, B., P. Brinck & G. Rudebeck (eds) South African Animal Life: Results of the Lund University Expedition in 1950–1951 vol. 8 pp. 9–197. Almqvist & Wiksells Boktryckeri Ab: Uppsala.

Staręga, W. 2009. Some southern African species of the genus Rhampsinitus Simon (Opiliones: Phalangiidae). Zootaxa 1981: 43-56.

Publication date of Bulletin de la Société Philomathique

I should say up front, this is going to be a pretty esoteric one. It's just that this is something I spent a fair chunk of a morning trying to work out, and I may as well put what I found up here in case someone else finds it useful.

A few weeks back I found myself, as one does, trying to sort out the exact publication date of early numbers of the Bulletin des Sciences, par la Societé Philomathique de Paris, which has been archived online at the Biodiversity Heritage Library. The Société Philomathique was an association of French scientists and polymaths from a wide range of disciplines founded in 1788. You can find the webpage for the current iteration of the Société here. In 1791, the Societé decided to circulate a bulletin of abstracts of their meetings, including summaries of papers and letters presented there.

The title page of the volume of the Bulletin available at the Biodiversity Heritage Library gives the dates of "Juillet 1791, a Ventôse, An 7", or July 1791 to February–March 1799, which is the dates of the meetings presented therein ("Ventôse, An 7" is a date in the Republican Calendar that was introduced for a period following the establishment of the French Republic in 1792). Citations I could initially find for individual notices in the Bulletin were all attributed to dates of the separate meetings that they were presented at (e.g. something presented at the May 1794 meeting would be cited as "1794"). But it was immediately obvious to me that the notices could not have been published at the times of the original meetings, at least not as they appeared in the volume reproduced, because abstracts from separate meetings would appear on the same page! Hence my search for information on the Bulletin's actual publication date: were notices for individual meetings issued separately at the time, or did they not actually appear in print until the subsequent publication (presumably in 1799 or even later) of the collected volume? I should note that some of the abstracts in the Bulletin included descriptions of new species, so the question of publication date could have further taxonomic implications.

A page from the collated Bulletin, showing how the last entry for the December 1792 meeting is followed immediately by the section for January 1793, without a page-break for originally separate issues to have been collected together.

Eventually, I was able to establish that separate Bulletin issues had indeed been released for each meeting (you can see reproductions of the uncollated originals at Gallica). However, there is a complication. Early issues of the Bulletin were written by hand, and distributed only to the members of the Société (about 18 people at the time). It was not until November 1792 that a printed version of the Bulletin began to be disseminated more widely. Now, the International Code of Zoological Nomenclature requires that any publication for taxonomic purposes produced before 1986 must "have been produced in an edition containing simultaneously obtainable copies by a method that assures...numerous identical and durable copies" (Article 8.1.3). A handwritten manuscript would not meet that requirement, so any zoological name appearing in those early bulletins would not count as published. They would not become established until the subsequent publication of the collated volume, which according to an introduction written by Jonathan Mandelbaum in 1977 for a bound collection of the original Bulletin issues (reproduced at Gallica here) happened in 1802.

Original first page of the Bulletin for January 1793. As well as the separation from the December entries, note that the first entry of the original version has been omitted from the collated version, and that the title's original spelling said 'Philomatique' rather than 'Philomathique'.

As an example of the sort of consequences that might arise from this, consider Odiellus spinosus, a widespread harvestman species found in western Europe. This species was very briefly described, as Phalangium spinosum, by Bosc in 1792 in one of the manuscript issues of the Bulletin de la Societé Philomatique (the February 1792 one, to be exact). This has uniformly been accepted as the publication date, but Bosc's species was not properly published until 1802. This might be a simple question of book-keeping, were it not that, in the meantime, Latreille (1798) had used the name 'Phalangium spinosum' for a quite different harvestman species, and described what is now known as 'Odiellus spinosus' under the name of 'Phalangium histrix'. So strict application of the law of priority means that the species in question should be known as Odiellus histrix.

Fortunately, in this case there may be some loopholes available to us. Latreille's names both have strict priority over Bosc's, but they may each count as nomina oblita ('forgotten names'). This is a provision in the ICZN that a name that has not been used as valid since before 1899 can be set aside in favour of a more widely recognised junior synonym if "the junior synonym or homonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years" (ICZN Art. 23.9.1.2). Latreille's Phalangium spinosum was soon recognised as a synonym of an earlier name, and was last used as valid in 1802. Phalangium histrix (or derived combinations thereof) persisted in the literature for longer, but I haven't come across it being used as a separate species after 1876. The open question is whether Bosc's name has been used often enough to warrant automatic conservation. I suspect it would have (I haven't done a proper tally myself, but a search for 'Odiellus spinosus' on Google Scholar brings up about 130 results) but, if not, then an appeal to the ICZN would be required if we wanted to keep using the current name for the species.

Long-legged Harvestmen of Southern Africa

New paper time!

Rhampsinitus conjunctidens, a new species of harvestmen from north-east South Africa, from Taylor (2017).

Taylor, C. K. 2017. Notes on Phalangiidae (Arachnida: Opiliones) of southern Africa with description of new species and comments on within-species variation. Zootaxa 4272 (2): 236–250.

When I first started research for my PhD thesis, *cough* years ago, I asked a number of museums if they could loan me their collections of monoscutid (now neopilionid) harvestmen. The species that I was interested in are found in Australia and New Zealand but when I opened a package of specimens sent to me from the California Academy of Sciences, I found a number of specimens from Africa in the mix. I immediately recognised what they were: not neopilionids, but representatives of another harvestment family, the Phalangiidae.

It seemed an easy enough error to make. Many species of southern African Phalangiidae resemble a lot of neopilionids in that the males have over-sized, elongate chelicerae. I referred to some of these species in the genus Rhampsinitus in an earlier post. To those not familiar with harvestmen diversity (which, let's face it, is the majority of people out there), the two groups can look very similar. True, the phalangiids are all distinctly much spikier than the neopilionids, but that doesn't seem that major a difference. To really see where they diverge from each other, you need to reach underneath the males' genital opercula and pull out their todgers.

Anywho, the specimens sat in storage for much longer than they should have, until I finally got around to looking them over in the latter part of last year. I then decided that it was worth writing them up into a short paper. Not only was there at least one new species among the specimens, they told me some very interesting things about variation within the species. Not only do Rhampsinitus species resemble Australasian neopilionids in their enlarged chelicerae, they resemble them in that individuals of a species vary in how enlarged the chelicerae are.

Major (left) and minor males of Rhampsinitus nubicolus, from Taylor (2013).

Now, I was not the first person to observe this point. Axel Schönhofer (2008) had already provided some detailed examples of variation in males of Rhampsinitus cf. leighi. I did, however, observe that the variation was even greater than Axel seemed to have recognised. Some of the least developed males of the species I was looking at had chelicerae that were pretty much no more developed than those of females. In some ways, the variation was even more remarkable than what I was familiar with in neopilionids. In most of the latter, major and minor males tend to be pretty similar to each other in features other than cheliceral development. In Rhampsinitus, we can see variation in almost all the features related to sexual dimorphism. In the species pictured immediately above, R. nubicolus, major males have massively long pedipalps as well as the long chelicerae; minor males have short, stubby pedipalps like those of a female. We can tell that they are the same species because they are found in the same location and have matching genitalia, but on the outside you would be hard pressed to pick them as such. Just to confuse matters even more, major males of two species may look very different to each other whereas minor males are externally almost identical. Without looking at the genitalia, it is all but impossible to identify which species a minor male belongs to.

As with the neopilionids, we can't yet say for sure what this variation means for the species' behaviour. In many other animal species with comparably varying males, large males will fight to protect and contain females while small males adopt a sneaking behaviour and try to spot females that are not being watched by large males. It seems quite possible that a similar thing is going on with Rhampsinitus. If you're a keen natural historian or behavioralist, there's something here that is crying to be looked into.

REFERENCE

Schönhofer, A. L. 2008. On harvestmen from the Soutpansberg, South Africa, with description of a new species of Monomontia (Arachnida: Opiliones). African Invertebrates 49 (2): 109–126.

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.

The Adaeines: South Africa's Cryptic Micro-Giants

Adaeulum sp., copyright Charles Haddad.

The Triaenonychidae are the family of Gondwanan harvestmen. While there are other families of harvestmen with a Gondwanan distribution (such as my own favoured family, the Neopilionidae), none of them are nearly as widespread and diverse as the triaenonychids. Despite their diversity, however, our understanding of triaenonychid relationships remains uncertain, and the family's classification poorly defined.

Within their range in Africa, Australasia and South America, triaenonychids can easily be distinguished from most other families of short-legged harvestmen by the structure of the claws on the hind two pairs of legs. Whereas members of other families bear a pair of simple claws on these legs, triaenonychids have a single claw with side branches on each leg. Branched claws are also found in the New Zealand genus Synthetonychia, which occupies its own distinct family, but that genus is easily recognised by its unusual body shape without a distinct eyemound. The Gondwanan Triaenonychidae were divided by Roewer into three subfamilies (Triaenonychinae, Triaenobuninae and Adaeinae) based on the shape of the sternum (the plate running along the underside of the body between the leg coxae). The significance of this feature was later questioned by Forster (1954) who recognised two subfamilies Triaenonychinae and Soerensenellinae on the basis of claw morphology (soerensenellines having longer side branches on the claws than triaenonychines) and reduced Roewer's subfamilies to tribes of Triaenonychinae. No large-scale analysis of triaenonychid phylogeny has been done so far, so it remains unestablished whether we should prefer one classification or the other (or possibly neither).

Typical triaenonychine (left) and adaeine (right) sternal shapes, from Forster (1954).

The Adaeinae or Adaeini may be one of the better defined of Roewer's original subgroups and recent authors have expressed the opinion that this may indeed turn out to be a natural clade. Whereas members of the Triaenonychinae sensu stricto and Triaenobuninae have a sternum that has a spearhead-shaped expansion at the front end and a broadened base at the back, members of the Adaeinae have a sternum that is a triangular or wedge shape without a posterior expansion. The adaeines are likely to be endemic to southern Africa; Kury et al. (2014) did list a single Australian species, Dingupa glauerti, in the Adaeinae but I would hazard a guess that future study proves this species to be misplaced (as has been found with other Australasian 'adaeines').

About forty species of adaeines are currently recognised, all from South Africa, but it is entirely likely that more remain to be described. The hard, granular body surface of adaeines inevitably picks up a covering of dirt and grit, making them exceedingly difficult to spot when not moving. Nevertheless, adaeines can be quite large as harvestmen go, with some being up to a centimetre in body length. Conversely, Micradaeum rugosum, a species found in the vicinity of Cape Town, is only about three-and-a-half millimetres in body length (Lawrence 1929). As with other species of Triaenonychidae, the large, raptorial pedipalps are larger and more robust in male adaeines than in females, and often have more pronounced spines. In some species of the genus Larifuga, nowever, spines or denticles may be more prominent on the female's pedipalps than on the male's, though the male's pedipalps are still larger and stronger overall (Lawrence 1937).

REFERENCES

Forster, R. R. 1954. The New Zealand harvestmen (sub-order Laniatores). Canterbury Museum Bulletin 2: 1–329.

Kury, A., A. Mendes & D. Souza. 2014. World checklist of Opiliones species (Arachnida). Part 1: Laniatores—Travunioidea and Triaenonychoidea. Biodiversity Data Journal 2: e4094. doi: 10.3897/BDJ.2.e4094

Lawrence, R. F. 1929. The harvest-spiders (Opiliones) of South Africa. Annals of the South African Museum 29 (2): 341–508.

Lawrence, R. F. 1937. The external sexual characters of South African harvest-spiders. Transactions of the Royal Society of South Africa 24 (4): 331–337, pls 14–15.

Metereca: Crossing the Divide

The crowdfunding campaign for my research on New Zealand harvestmen is still active. So far we're about 25% of the way towards the goal! Please click on the link above, and do your part to support your favourite arachnologist.

Dorsal view and pedipalp of Metereca papillata, from Roewer (1935).

There can be little doubt that the continent with the least studied harvestmen fauna relative to its likely diversity is Africa. Africa is home to a wide range of harvestmen lineages, some of which are found nowhere else on earth, but many remain unrevised. Among these poorly known elements are numerous members of the family Assamiidae. Among these are the members of the genus Metereca, which I drew as the semi-random subject for this post.

The Assamiidae are a family of short-legged harvestmen found in tropical regions of the Old World: Africa, Asia and Australia. I've spoken enough in the past about the shadow of Carl-Friedrich Roewer that hangs heavy over harvestmen systematics. Recent years have seen a large amount of research being conducted on the harvestmen of the Neotropics, resulting in a vast improvement in our taxonomic understanding for that part of the world. The harvestmen of the Old World, unfortunately, are yet to attract the same attention. Assamiids were last extensively reviewed by Roewer in 1935. He divided them between 17 subfamilies but in the usual Roewerian way these were mostly based on fairly superficial features (numbers of subsegments in the leg tarsi, whether the palp femur has long spines or only short denticles, etc.) that may not be that significant. Staręga (1992) published a checklist of African harvestmen in which he synonymised assamiid 'genera' that Roewer had placed in separate subfamilies, thus implicitly synonymising the subfamilies they were tied to.

Metereca is a genus of about fifteen known species of assamiid found across Africa. Roewer (1935) placed it in his subfamily Erecinae, supposed features of which included simple claws and the absense of a pseudonychium (a 'false claw' between the two real claws) on the third and fourth tarsi, two subsegments in the first telotarsus, small denticles on the pedipalp femur, concealed spiracles, and no median spine on the front margin of the carapace. However, the Erecinae as defined in this way included genera from all three of the Old World continents. Considering that other harvestmen groups have turned out to have a strong correlation between geography and phylogeny, I'd be willing to put money on Roewer's Erecinae not being monophyletic.

That same doubt applies to Metereca (though I'm not sure I'd put money on it this time), which is one of the larger erecine genera currently recognised. Supposed features of Metereca include a lack of dorsal spines on the body, and a four-segmented first tarsus and two-segmented second telotarsus. Species have been assigned to this genus from widely separated parts of the continent: the Congo, Tanzania, Mozambique. But not only is this a genus defined primarily by the absence of features (always a bit suspect), but other groups of harvestmen have tended to show a division between western and eastern Africa. It would be worth someone's time in the future, I think, to confirm whether Metereca really does cross the divide that others don't.

REFERENCES

Roewer, C. F. 1935. Alte und neue Assamiidae. Weitere Weberknechte VIII. (8. Ergänzung der "Weberknechte der Erde" 1923). Veröffentlichungen aus dem Deutschen Kolonial- und Uebersee-Museum in Bremen 1 (1): 1–168, pls 1–9.

Staręga, W. 1992. An annotated catalogue of Afrotropical harvestmen, excluding the Phalangiidae (Opiliones). Annals of the Natal Museum 33 (2): 271–336.

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.

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.