Austrotritia: Jack-in-the-Box Mites

We just keep coming back to the oribatids, don't we?

In an earlier post, I introduced you to Oribotritia, one of the genera of box mites. These, you may recall, are the armoured mites that have evolved the ability to curl the front of the body under themselves and tuck back their legs to form a solid case (in the Oribotritiidae, that mechanical defense is supplemented by the production of a defensive chemical, chrysomelidial, from glands in the cuticle—Shimizu et al. 2012). In the earlier post, I also gave you a quick overview of the families of what are known as the 'true' box mites. Today's post is for another component of the family Oribotritiidae, the genus Austrotritia.

Austrotritia lebronneci, copyright R. Penttinen.

Austrotritia accounts for nearly twenty species of box mite, the great majority of which are found in Australasia and southern and eastern Asia (Liu et al. 2009). Outliers are A. engelbrechti in South Africa, A. herenessica in the Canary Islands and, most unexpected of all, A. finlandica in Finland. Austrotritia differs from all other oribotritiids except the small Bornean genus Terratritia in lacking any division between the genital and aggenital plates on the underside of the body. The distinction between Austrotritia and Terratritia perhaps requires reassessment: Niedbała (2000) distinguished them by the presence of five-segmented palps and a single pair of exobothridial setae in Austrotritia versus three-segmented palps and two pairs of exobothridial setae in Terratritia (the bothridia are the structures bearing large sensory setae on the prodorsum of the mite; exobothridial setae are thus setae sitting alongside the bothridia). However, Liu & Zhang (2014) redescribed the widespread species Austrotritia lebronneci as having three-segmented palps but only a single pair of exobothridial setae. Note that classification of oribatids has mostly been conducted from a diagnostic rather than a phylogenetic perspective; it would not surprise me if Terratritia turned out to be a derived subgroup of Austrotritia.

Schematic of jump performance by Indotritia cf. heterotrichia from Wauthy et al. (1998); the solid line represents observed jumps, the dashed lines modelled jumps. Line drawings represent (a) body posture when beginning jump, (b) rotation during jump, and (c) enclosed posture after jumping.

As well as the aforementioned defenses standard for box mites, Austrotritia and the related genus Indotritia stand out from other oribotritiid genera in that at least some species have the ability to jump. The mechanics of jumping were described for a species of Indotritia by Wauthy et al. (1998) who recorded the mites jumping nearly a centimetre in height over a distance of just under an inch (for perspective, the mite itself is about half a millimetre in length). Jumping was preceded by compressing the notogaster while raising the ventral plates under the opisthosoma, together with lowering the prosoma and bringing the legs together under the body. Small hooks at the end of femur of the first pair of legs were used to catch ridges on the side of the prodorsum in order to hold the body compression. The force for the jump was presumably supplied by the release of the hydraulic compression of the body fluids when the legs disengaged from the prodorsum, propelling the mite backwards while the body rolled forwards: essentially, the mite would star-jump away. The mite would curl up after jumping to lie in an enclosed state.

Whether all Austrotritia species are jumpers is not entirely certain. The femoral hooks that seem to play a significant role in jumping have not been described in all species. However, it is not clear if this lack of observation represents an actual absence or whether this minute feature has simply been overlooked. I also wonder whether the aforementioned fusion of the ventral plates in Austrotritia is related to their jumping abilities (Indotritia species also have the genital and aggenital plates fused anteriorly though they retain a degree of separation at the rear of the plates; non-jumping Oribotritia have the plates entirely separated). As always, there's still a lot we could potentially find out.

REFERENCES

Liu, D., J. Chen & G. Qiao. 2009. Review of Austrotritia (Acari: Oribatida: Oribotritiidae), with descriptions of two new species from China. Zootaxa 2144: 54–64.

Liu, D., & Z.-Q. Zhang. 2014. Redescription of Austrotritia lebronneci (Oribotritiidae) and descriptions of two new species of Euphthiracaridae (Acari, Oribatida) from Australian region. International Journal of Acarology 40 (1): 43–51.

Niedbała, W. 2000. The ptyctimous mites fauna of the Oriental and Australian regions and their centre of origin (Acari: Oribatida). Polskie Towarzystwo Taksonomiczne: Wrocław (Poland).

Shimizu, N., R. Yakumaru, T. Sakata, S. Shimano & Y. Kuwahara. 2012. The absolute configuration of chrysomelidial: a widely distributed defensive component among oribotritiid mites (Acari: Oribatida). Journal of Chemical Ecology 38: 29–35.

The Ornithocheyletiini: Making a Living off Birds

In an earlier post, I commented on the carnivorous mites of the family Cheyletidae. These rapacious micropredators are commonly associated with the nests and burrows of terrestrial vertebrates, attacking debris-feeders drawn in by the host's leavings. With such a close association already in place, it should come as little surprise that some lineages within the Cheyletidae have learnt to bypass scavenger predation and go directly to the source, becoming parasites of the vertebrate hosts themselves.

Slide-mounted female of Bakericheyla chanayi (left; scale bar = 50 µm) and nest webs on the skin of a heavily parasitised chaffinch Fringilla coelebs (right), from Filimonova (2013).

One such lineage is the Ornithocheyletiini, members of which are parasites of birds. Like other parasitic cheyletids, ornithocheyletiins have a relatively small, simple gnathosoma (the 'head' of the mite), no eyes, and lack the large, pectinate, claw-like setae found on the palps of free-living predatory cheyletids (instead, the setae at this position are small and smooth though they do still have hooked ends). Ornithocheyletiins are further distinguished from other cheyletids by having particularly large claws at the end of each leg that are overhung by a well developed knob on the end of the tarsus (Bochkov & Fain 2001).

Ornithocheyletiins live on the skin of their bird hosts. In the genera Ornithocheyletia and Bakericheyla, the mites spin a protective web beneath which they live and feed. Members of the tribe have been recorded from a number of bird orders, mostly smaller land birds (Passeriformes, Columbiformes, Piciformes, Coraciiformes, Psittaciformes and Apodiformes). At least one species of Ornithocheyletia was described from the Natal spurfowl Pternistis natalensis, a galliform. Members of the genus Apodicheles are restricted to species of Apodiformes (swifts) but other genera are found on a wider range of hosts. One cosmopolitan species, Bakericheyla chanayi, has been found on hosts of both the orders Passeriformes and Coraciiformes. The exact method of exploiting their host may vary: species of Bakericheyla feed on blood whereas Ornithocheyletia species feed on lymph fluid.

Historically, parasitic cheyletids were treated as a separate family Cheyletiellidae but are now classified with their free-living relatives. The exact relationships between free-living and parasitic cheyletids remain open to question. A morphological phylogenetic analysis of cheyletids by Bochkov & Fain (2001) did recover the parasitic forms as a clade but this result was questioned by the authors themselves. Instead, they suggested that the various parasitic tribes of Cheyletidae represented independent lineages whose shared features represented convergent adaptations to the parasitic lifestyle. The Ornithocheyletiini might, for instance, be compared to tribes such as the Cheletosomatini that inhabit the quills of bird feathers but feed on other quill-inhabiting mites rather than the birds themselves. Did ornithocheyletiins evolve from using birds as hunting grounds to using birds as food, or did they carry their parasitic habits with them from some other host?

REFERENCE

Bochkov, A. V., & A. Fain. 2001. Phylogeny and system of the Cheyletidae (Acari: Prostigmata) with special reference to their host-parasite associations. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Entomologie 71: 5–36.

Mites of Marine Sands

Mites may be the most ecologically diverse group of animals on the planet. It is something of a challenge to think of a habitat supporting complex life in which mites may not be found. Nevertheless, it can fairly be said that the marine environment has provided them with a challenge. Though a wide variety of mites can be found in habitats along the shoreline, few lineages have learnt to make a life for themselves beyond the littoral fringe. The most diverse group of truly marine mites is the Halacaridae, of which the genus Simognathus is a representative.

Simognathus sp., from Banks (1915).

Halacarids are notably armoured mites, their bodies protected by an array of reticulate plates. They are found in a wide range of marine habitats and pursue the gamut of lifestyles: representatives of halacarids include algal grazers, micropredators, and parasites. Despite their aquatic lifestyle, they are not swimmers. Instead, they cling to their substrate and crawl slowly on legs bearing large claws. The diversity of halacarid morphologies is reflected in their classification with over a dozen subfamilies currently recognised.

Simognathus is a genus of halacarids found around the world though the greater diversity of species are known from the Southern Hemisphere. They are found at depths ranging from near the low tide mark to around 500 m, and from the full range of tropical, warm-temperate and cold-temperate waters. Bartsch (2005) speculated that the only reason they are not known from even colder waters may be a question of sampling effort rather than true absence. Most Simognathus species are known to live among coarse sand, or in other interstitial microhabitats such as among coral rubble, among colonies of sessile animals such as barnacles or tubeworms, or within algal holdfasts. I haven't come across any specific comments on their diet but their robust chelicerae and grasping fore legs leads me to suspect that Simognathus species are probably micropredators.

Simognathus and the closely related genus Acaromantis form the subfamily Simognathinae. Simognathines differ from other halacarids in their spindle-shaped body with short rostrum, reflecting their interstitial habitat. The first leg ends in a pincer arrangement formed from the terminal claw and a spine on the underside of the tibia. Acaromantis species have a two-segmented palp, no lateral claws at the end of the first leg, and a spinose seta on the genu (the segment between the femur and tibia) of the first leg. Simognathus species have a three-segmented palp, a pair of slender lateral claws on the first leg as well as the terminal claw, and no spinose seta on the first genu. The defining features of Simognathus are all likely to be primitive relative to those of Acaromantis and it has been suggested for some time that Acaromantis may be a derived subgroup of Simognathus. This suggestion is bolstered by a recent molecular analysis of halacarids by Pepato et al. (2018) which found the two Simognathus representatives included to be paraphyletic to the included species of Acaromantis.

REFERENCES

Bartsch, I. 2005. Lohmannella and Simognathus (Halacaridae: Acari) from Western Australia: description of two new species and reflections on the distribution of these genera. Records of the Western Australian Museum 22: 293–307.

Pepato, A. R., T. H. D. A. Vidigal & P. B. Klimov. 2018. Molecular phylogeny of marine mites (Acariformes: Halacaridae), the oldest radiation of extant secondarily marine animals. Molecular Phylogenetics and Evolution 129: 182–188.

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.

The Running of the Crabs

There are many varieties of spider in the world that, while not necessarily uncommon, tend to be little known to the general public owing to their cryptic and retiring nature. As an example, meet the genus Philodromus.

Philodromus cespitum, copyright R. Altenkamp.

Philodromus is the largest genus recognised in the family Philodromidae, commonly referred to as the running crab spiders or small huntsman spiders. About 250 species have been assigned to this genus from various parts of the world (Muster 2009), mostly in the Holarctic region. Like the huntsman spiders of the Sparassidae and the crab spiders of the Thomisidae, philodromids are an example of what old publications often referred to as 'laterigrade' spiders, in which the legs are arranged to extend sideways from the body more than forwards and backwards. They have eight eyes arranged in two recurved rows of four. Philodromids differ from crab spiders in having scopulae (clusters of hairs that can look a bit like little booties) on the leg tarsi, and having secondary eyes that lack a tapetum (reflective layer). They differ from huntsmen in that the junction between the tarsi and metatarsi is restricted to movement in a single plane, rather than the tarsus being able to move freely (Jocqué & Dippenaar-Schoeman 2007). Philodromids do not build a web to capture prey but instead seize prey directly.

The distinction between Philodromus and other genera in the family has historically been imprecise (Muster 2009) which goes some way to explaining the large number of species it has encompassed. In general, though, the eye rows of Philodromus are relatively weakly recurved, and its body form is less slender than that of the genera Tibellus and Thanatus. These may well be primitive features for the family, and a phylogenetic analysis of philodromids by Muster (2009) indicated that at least one group of species historically included in Philodromus (the P. histrio group) may be more closely related to the slender-bodied genera. The great French arachnologist Eugene Simon recognised several species groups in Philodromus, distinguished by features such as eye arrangement and leg spination, but recent authors feel that the status of these groups requires further investigation before we could consider treat?ing them as distinct genera.

Philodromus dispar, copyright Judy Gallagher.

Most species of Philodromus live on vegetation, flattening themselves against stems and foliage to avoid detection. As with other laterigrade spiders, the arrangement of their legs allows for rapid sideways movement, perfect for avoiding predators or turning up where prey do not expect them. At least one species group found in the Mediterranean region (including P. pulchellus and its relatives) differs in being ground-living, with a predilection for salt flats (Muster et al. 2007). Bites to humans from Philodromus appear to be vanishingly rare: a report on such a bite by Coetzee et al. (2017) appears to be the first record of one (the bite was painful, causing swelling and some ulceration, but without long-term effects following treatment). Philodromus species are much more likely to have a net positive value to humans, as they may act as control agents for insect pests among crops and orchards.

REFERENCES

Coetzee, M., A. Dippenaar, J. Frean & R. H. Hunt. 2017. First report of clinical presentation of a bite by a running spider, Philodromus sp. (Araneae: Philodromidae), with recommendations for spider bite management. South African Medical Journal 107 (7): 576–577.

Jocqué, R., & A. S. Dippenaar-Schoeman. 2007. Spider Families of the World. Royal Museum for Central Africa: Tervuren (Belgium).

Muster, C. 2009. Phylogenetic relationships within Philodromidae, with a taxonomic revision of Philodromus subgenus Artanes in the western Palearctic (Arachnida: Araneae). Invertebrate Systematics 23: 135–169.

Muster, C., R. Bosmans & K. Thaler. 2007. The Philodromus pulchellus-group in the Mediterranean: taxonomic revision, phylogenetic analysis and biogeography (Araneae: Philodromidae). Invertebrate Systematics 21: 39–72.

The Camisiids: Cryptic Inhabitants of Soil and Wood

Various views of Camisia biverrucata, copyright Pierre Bornand.

The animal in the above pictures is a typical representative of the Camisiidae, a widely distributed family of oribatid mites. Members of this family can be found in soil, on the trunks of trees, or hidden among mosses and lichens. They are slow-moving animals and are often concealed from potential predators by an encrusting layer of dirt and organic debris. Carrying this encrusting layer may be related to a reduction in the offensive chemical-producing glands that are used by many other oribatids for defense (Raspotnig et al. 2008). In members of the genus Camisia, the openings of these glands are completely covered by dirt, but in the genera Platynothrus and Heminothrus the openings still protrude above the encrustation. The recently described Paracamisia osornensis, which does not carry an encrusting layer, retains a large offensive gland (Olszanowski & Norton 2002).

Close to 100 species have been assigned to this family; though found in most parts of the world, camisiids are most diverse in the Northern Hemisphere. One species in particular, Platynothrus peltifer, is almost global in distribution and the range of habitats in which it has been found includes soil, litter, peat and even aquatic habitats (Norton & Behan-Pelletier 2009) When one is as small and metabolically undemanding as these animals are, there may be surprisingly little difference between being out in the air or immersed in water, and even primarily terrestrial oribatids may survive submersion almost indefinitely. Genetic studies of P. peltifer have identified a high level of within-species divergence and it has been calculated on this basis that this species may have survived almost unchanged in external appearance for some 100 million years (Heethoff et al. 2007).

The ubiquitous Platynothrus peltifer, copyright Centre for Biodiversity Genomics.

The Camisiidae are closely related to another oribatid family, the Crotoniidae, that is found in South America and Australasia. One of the more significant differences between the two families is that whereas the camisiids appear to be entirely parthenogenetic, crotoniids reproduce sexually. Recent analyses, both molecular and morphological, indicate that the 'camisiids' are paraphyletic with regard to the crotoniids, leading Colloff & Cameron (2009) to treat the latter as a subfamily, Crotoniinae, of the former. This re-classification has been accepted by other authors though the law of priority requires that the combined family should be known as the Crotoniidae, not Camisiidae. The nested position of the sexual crotoniines within the asexual 'camisiids', with other related oribatid families also being asexual, has led to the suggestion that the crotoniines have somehow re-evolved sexuality. This would be fascinating if true, seemingly violating the usual principle that complex features can't be re-evolved once lost. Personally, I tend to be sceptical of claims like this (see this old post, for instance). I would like to see evidence beyond simple phylogenetic position to indicate if this is a true re-evolution rather than an historical bias towards loss of sexuality giving a misleading image.

REFERENCES

Colloff, M. J., & S. L. Cameron. 2009. Revision of the oribatid mite genus Austronothrus Hammer (Acari: Oribatida): sexual dimorphism and a re-evaluation of the phylogenetic relationships of the family Crotoniidae. Invertebrate Systematics 23: 87–110.

Heethoff, M., K. Domes, M. Laumann, M. Maraun, R. A. Norton & S. Scheu. 2007. High genetic divergences indicate ancient separation of parthenogenetic lineages of the oribatid mite Platynothrus peltifer (Acari, Oribatida). Journal of Evolutionary Biology 20: 392–402.

Norton, R. A., & V. M. Behan-Pelletier. 2009. Suborder Oribatida. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3^rd ed. pp. 430–564. Texas Tech University Press.

Olszanowski, Z., & R. A. Norton. 2002. Paracamisia osornensis gen. n., sp. n. (Acari: oribatida) from Valdivian forest soil in Chile. Zootaxa 25: 1–15.

Raspotnig, G., E. Stabentheiner, P. Föttinger, M. Schaider, G. Krisper, G. Rechberger & H. J. Leis. 2008. Opisthonotal glands in the Camisiidae (Acari, Oribatida): evidence for a regressive evolutionary trend. Journal of Zoological Systematics and Evolutionary Research 47 (1): 77–87.

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.

Ferreting up a Bird's Nose

Mites, as I may have commented before, seem to have an almost fractal level of diversity: the closer you look, the more there is of it. This is nowhere more apparent than when it comes to parasitic mites which infest almost any host in any way that you can imagine. For the subject of this post, I drew one such mite: the honeyeater nasal mite Ptilonyssus myzanthae.

Venter (left) and dorsum of female Ptilonyssus myzanthae, from Domrow (1964). The scale bar equals 500 µm.

Bird nasal mites of the family Rhinonyssidae are, as their name indicates, inhabitants of the nasal passages of birds. General adaptations of the family for their parasitic lifestyle include tendencies towards reduction of the body sclerotisation and reduction in the length and number of setae. They use the claws on their front legs to tear openings in the host's mucous membranes and then feed on its blood. Transmission of nasal mites seems to happen during bill-to-bill contact such as when parents are feeding their young or during mating activities, or indirectly through water or on the surface of perches or the like. Rhinonyssid nasal mites are not known to transmit any actual diseases between hosts but they can cause the formation of lesions or inflammation or the like. All in all, probably not very pleasant for the bird (see here for some more details).

Whole-body illustration of a different rhinonyssid species, from Greg Spicer.

Nevertheless, infection rates in bird populations can be very high and most (if not all) bird species will be host to some nasal mite species. Most species of nasal mite are very host specific, known on only one or a few bird species (it must be noted, though, that the question of just how many researchers choose to look up a bird's schnozz in search of mites may not be irrelevant here). Ptilonyssus myzanthae was described by Domrow (1964) from two species of honeyeater in Queensland, Australia: the noisy miner Manorina melanocephala and the little wattlebird Anthochaera chrysoptera. Distinctive features of this species compared to others in the genus include a subhexagonal anterior dorsal shield on the body, a narrow genital shield, and a divided pygidial shield (the small pair of shields near the rear of the dorsum). Both of the known hosts are widespread and common in eastern Australia and it is likely that this mite is similarly ubiquitous. Studies of honeyeater phylogeny tend to place the genera Manorina and Anthochaera as close relatives, so it is possible that P. myzanthae has been infesting them since before their lineages diverged. It would be worth looking for the species in other related honeyeaters to see if we find any further clues.

REFERENCE

Domrow, R. 1964. Fourteen species of Ptilonyssus from Australian birds (Acarina, Laelapidae). Acarologia 6 (4): 595–623.

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.

Neostrinatina mixoppia

Dorsum of Neostrinatina mixoppia, from Mahunka (1978).

Time for another oribatid. This is Neostrinatina mixoppia, a species described as the only member of its genus by S. Mahunka in 1978. It was described on the basis of two specimens from near Coban in the highlands of Guatemala. Neostrinatina belongs to the family Oppiidae, a group of often smaller oribatids with moniliform legs, and is a bit over a quarter of a millimetre in length. N. mixoppia noticeably differs from other oppiids in its long pectinate sensillus on either side of the prodorsum. The other dorsal setae are also particularly long and barbed. Other distinctive features of this species, according to Mahunka, are a pair of lateral teeth on the dorsosejugal suture (the junction between the prodorsum and the notogaster, or what one might think of as the 'head' and 'body' regions of the dorsum) that jut towards the sensilli, and an 'enormous, spiniform excrescence' projecting forwards from the anogenital region. I must admit, though, I've been trying to interpret Mahunka's illustration of the ventral region of N. mixoppia and I'm still not entirely sure what this latter feature looks like. Like other oppiids, the prodorsum does not have the projecting lamellae found in many oribatid families; instead, N. mixoppia has a pair of branching costulae (thickened ridges). The legs each end in a single claw.

Venter of Neostrinatina mixoppia, from Mahunka (1978).

Oppiids are currently recognised as the most diverse family of oribatids with over 1000 known species, the greater number of these found in the tropics. Though the ecology of N. mixoppia itself is unknown, other oppiids feed on fungi. The single claws on the legs suggest a terrestrial habitat. As with many (if not most) oribatid groups, the relationships of oppiids are in great need of revision with many genera being arranged on the basis of potentially convergent characters. Mahunka himself recognised this in his description of N. mixoppia, expressing the opinion that it represented '? mixture of at least three present day " genera"'. The number of dorsal setae suggested one genus, the dorsosejugal teeth suggested another. Perhaps one day we'll know which is which.

REFERENCE

Mahunka, S. 1978. Neue und interessante Milben aus dem Genfer Museum XXV. On some oribatids collected by Dr. P. Strinati in Guatemala (Acari: Oribatida). Acarologia 20 (3): 133–142.

The Tiny Lurking Fear

The world of micro-organisms can be a cut-throat one. Minute grazers are under constant threat from minute predators. It can be an existence red in tooth and claw or, in the case of today's subjects, haemolymph-covered in chelicera and grasping seta.

The domestic cheyletid Cheyletus eruditus, from here.

The Cheyletini are one of fifteen tribes recognised by Bochkov & Fain (2001) in the mite family Cheyletidae. Cheyletids are small mites, generally less than half a millimetre in length, that are close relatives of the follicle mites seen on this site previously. Many cheyletids (including most Cheyletini) are, nonetheless, voracious predators of other mites. Other members of the family live as parasites on birds or mammals. In the past, such parasitic forms were recognised as a distinct family Cheyletiellidae but it is now recognised that they are descended from predatory ancestors, possibly on more than one occasion.

Predatory cheyletids are not to be sniffed at: the Hemicheyletia wellsina nymph on the left has managed to bring down another much larger predatory mite Metaseiulus occidentalis. Copyright Haleigh Ray.

The Cheyletini can be considered representative of this ancestral form; indeed, as members of the tribe are distinguished from others in the family solely by their retention of features likely to be primitive, it is likely to be non-monophyletic (Bochkov & Fain 2001). Cheyletini have more or less oval or oblong bodies with moderate-length legs, shorter than the length of the body, all tipped by a claw. The gnathosoma (the front section of the body bearing the chelicerae and palps) is well developed and generally makes up a full third of the body length. The palps are the real business end of a cheyletin, though. In many groups of prostigmatic mites, the last segment of the palp (the tarsus) is offset from the main line of the appendage and opposed to a large claw at the end of the tibia, the two of them together functioning to grab whatever the mite wishes to grab. Predatory cheyletids have the tibial claw and offset tarsus but the tarsus also bears a number of intimidating enlarged, claw-like setae that add to the mite's grabbing power. In the Cheyletini, there are four such setae at the end of the tarsus, a pair of comb-like setae dorsally and a pair of sickle-shaped setae ventrally. The mite will generally sit in place, motionless, with its palps held open. Should a potential prey animal come close enough to the predator, the palps will swing together and the prey will be caught.

Cheyletini are diverse in habitat. Many genera are free-ranging hunters on trees but others show preferences for more constrained locales. In particular, a group of genera centred around the type genus Cheyletus includes species living in the nests and burrows of mammals and birds. Most of these species benefit their hosts by hunting down potential parasites and the like or cleaning up organic residue. One genus, Cheletophyes, is found in the nests of carpenter bees Xylocopa and can actually be transported between nests by the host bee in special pockets on the thorax called acarinaria. However, it is not that big a step to take from feeding on shed organic particles in the host's nest to feeding more directly on the host itself and this is presumably how some cheyletids made the switch to parasitism. One member of the Cheyletini, Pavlovskicheyla platydemae, is an ectoparasite of tenebrionid beetles, attaching to them in spots concealed beneath the host elytra (Walter et al. 2009).

Female Hemicheyletia wellsina patrolling near her batch of eggs (in the upper left, under a protective silk covering she has woven for them), copyright Haleigh Ray.

Other Cheyletus species are known from human-associated habitats such as in houses or grain stores where, again, they are usually considered a net benefit due to their controlling effect on pests such as dust mites or flour mites. Indeed, the common species Cheyletus eruditus has been commercially marketed for control of stored product pests under the name Cheyletin. Females of this species in domestic habitats lay their eggs in crevices or other such concealed spaces and remain to guard their brood, driving away other animals that may pose a threat. However, hatching offspring need to disperse quickly, as if they hang around the nesting site too long they may be eaten by the mother herself (Walter & Krantz 2009).

REFERENCES

Bochkov, A. V., & A. Fain. 2001. Phylogeny and system of the Cheyletidae (Acari: Prostigmata) with special reference to their host-parasite associations. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Entomologie 71: 5–36.

Walter, D. E., & G. W. Krantz. 2009. Oviposition and life stages. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3^rd ed. pp. 57–63. Texas Tech University 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 3^rd ed. pp. 233–420. Texas Tech University Press.

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.

False Spider Mites

Among the enormous diversity of the world's mites, some families are particularly notorious for the damage that they inflict on commercial plant crops. Among such Acari non grata are the spider mites of the family Tetranychidae or the gall mites of the Eriophyidae. But a third, equally notorious group is the false spider mites or flat mites of the Tenuipalpidae.

Red and black flat mite Brevipalpus phoenicis, false-colour SEM by Christopher Pooley.

False spider mites include about 800 known species of more or less flattened, slow-moving mites. They are closely related to the true spider mites and both families have the chelicerae modified into a pair of long, whip-like retractable stylets that are used to pierce and suck fluids from plant tissues. In the case of the false spider mites, though, their commercial infamy comes not only from the direct damage caused by the feeding mites themselves but also from the effects of transmitted viruses. Viruses transmitted by false spider mites include the causative agents of diseases such as citrus leprosis and coffee ring spot and may cause significant reductions in the yield and lifespan of infected plants.

Morphologically, false spider mites differ from true spider mites in the absence of what is called the 'thumb-claw' process, an arrangement of the tarsus of the pedipalp alongside a claw on the tibia (hence the family name which means 'slender palp'). The palps are often reduced, with some species having only the barest remnant. Some species also show reduction in the fourth pair of legs, and females of a number of species are six-legged as adults. This merely stands as another example of how mite morphology functions purely to play silly buggers with anything one might learn in basic animal biology.

Hebe stem gall mites Dolichotetranychus ancistrus inside an open gall, copyright Plant and Food Research.

Parthenogenesis is also common in false spider mites. Species found in cooler climes will often overwinter as females, with a new generation of males not appearing until the next spring. In some species, eggs produced parthenogenetically will hatch into males; in others, they will produce females. A few species almost entirely lack functional males. A small group of these species in the genus Brevipalpus is unique among animals in being both parthenogenetic and genetically haploid.

Almost all forms of seed plant seem to be vulnerable to some form of flat mite or another; some mite species are very catholic in their tastes and will latch onto almost anything green and photosynthesising. Others are more discerning. How false spider mites make their way from one host plant to another is little known but they may be passively carried through the air on the wind. Alternatively, they may be inadvertently carried from place to place by feeding herbivores, or by the very human horticulturalists that suffer so much from their presence.

REFERENCE

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.

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.

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.