Amphiascus: Can a Copepod be a Friend of Mine?

Amphiascus sp., copyright Alexandra.

The animal shown in the image above is a member of Amphiascus, a cosmopolitan genus of about thirty known species of benthic harpacticoid copepods. Amphiascus is a genus of the family Miraciidae; in older texts, you will find it referred to the Diosaccidae, but this family is now regarded as a synonym of the former. Miraciids are somewhat elongate harpacticoids generally with a fusiform body shape and females with paired egg sacs; as with other copepod taxa, their specific characterisation depends on fairly fine characters of the appendage setation (Willen 2002). Wells et al. (1982) placed Amphiascus in association with a group of related genera in the miraciid family tree on the basis of its retention of a fairly extensive setation on the pereiopods, two inner setae on the endopod of pereiopod II in females, and two articulated claws on that segment in males. However, the proposed phylogeny of Wells et al. provides no apomorphies for Amphiascus itself, implying that it is characterised only by plesiomorphies relative to related genera.

The title of this post refers to the circumstances surrounding the discovery of a relatively recently described Amphiascus species, A. kawamurai Ueda & Nagai 2005. In the cultivation in Japan of nori, the edible alga used (among other things) in wrapping sushi rolls, the conchocelis phase of the life cycle is grown on oyster shells in outdoor tanks of seawater (like many algae, nori goes through an alternation of generations, with its life cycle including two very distinct forms; as well as the familiar large flat alga, the life cycle of nori includes a small filamentous shell-boring stage, initially mistaken for a distinct organism and called Conchocelis). Unfortunately, the oyster shells may also become overgrown with diatoms, retarding the growth of conchocelis. As a result, nori growers may be required to laboriously scrub the shells of diatoms several times over the conchocelis growth period. However, it was noticed in Ariake Bay in Kyushu that some form of copepod would sometimes appear in the nori tanks, presumably brought in with seawater from the bay. When this copepod was present, it would graze on the diatoms, reducing the need for other controls. Study of the nori-tank copepod revealed it to be a previously undescribed species, revealing once more that even the species we are not aware of have the potential to directly improve our lives.

REFERENCES

Ueda, H., & H. Nagai. 2005. Amphiascus kawamurai, a new harpacticoid copepod (Crustacea: Harpacticoida: Miraciidae) from nori cultivation tanks in Japan, with a redescription of the closely related A. parvus. Species Diversity 10: 249–258.

Wells, J. B. J., G. R. F. Hicks & B. C. Coull. 1982. Common harpacticoid copepods from New Zealand harbours and estuaries. New Zealand Journal of Zoology 9 (2): 151–184.

Willen, E. 2002. Notes on the systematic position of the Stenheliinae (Copepoda, Harpacticoida) within the Thalestridimorpha and description of two new species from Motupore Island, Papua New Guinea. Cah. Biol. Mar. 43: 27–42.

The Chromeurytominae: Australo-Asian Mystery Wasps

One of the most diverse groups of micro-wasps is the Chalcidoidea, a bewildering array of intricate little jewels. A number of chalcidoid taxa have been extensively studied due to their roles as parasitoids of insect pests, but there are also many groups of chalcidoids that remain little known. One such group is the Chromeurytominae.

Male Chromeurytoma sp., copyright John Heraty.

The Chromeurytominae are a small group of chalcidoids primarily known from Australia, where they are represented by two genera, fourteen species of Chromeurytoma and the monotypic Asaphoideus niger (Bouček 1988). A single species, Pitayana coccorum, has also been described from Bangladesh (Bouček & Bhuiya 1990). Characteristic features include a relatively large subrectangular pronotum (the first segment of the thorax) and an antenna with six segments between the pedicel and the clava (the club). They are more or less shiny, often with a blue or green metallic gloss, and the gaster is fairly robust and does not collapse in preserved specimens. The affinities of the Chromeurytominae have been rather uncertain and the subfamily was only established by Bouček in 1988. Chromeurytoma itself was originally described in the family Eurytomidae, with which it shares the large pronotum. Other features suggest a relationship with the family Torymidae, such as an occipital carina (a ridge around the back of the head) and prominent cerci. Currently the Chromeurytominae are treated as part of the family Pteromalidae, which is not really saying too much. As our understanding of chalcidoid phylogeny has improved in recent years, it has largely confirmed what many workers had long suspected: that once you account for the other families, the Pteromalidae is pretty much just what's left over. Nevertheless, the broad-scale analysis of chalcidoids by Heraty et al. (2013) places the Chromeurytominae within a cluster of 'pteromalid' subfamilies, closer to the type subfamily Pteromalinae than to either the Eurytomidae or Torymidae.

The chromeurytomines are a bit of a mixed bag in terms of host species, but there is the common thread that their hosts are immobile or semi-sedentary plant-feeding insects. Pitayana coccorum attacks mealybugs and other soft scales, with multiple larvae potentially developing on a single host. Asaphoideus niger attacks the citrus leaf-miner Phyllocnistis citrella. The Chromeurytoma species are associated with galls on trees such as Eucalyptus; presumably they are parasites of the insects forming the galls.

REFERENCES

Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

Bouček, Z., & B. A. Bhuiya. 1990. A new genus and species of Pteromalidae (Hym.) attacking mealybugs and soft scales (Hom., Coccoidea) on guava in Bangladesh. Entomologist's Monthly Magazine 126: 231–235.

Heraty, J. M., R. A. Burks, A. Cruaud, G. A. P. Gibson, J. Liljeblad, J. Munro, J.-Y. Rasplus, G. Delvare, P. Janšta, A. Gumovsky, J. Huber, J. B. Woolley, L. Krogmann, S. Heydon, A. Polaszek, S. Schmidt, D. C. Darling, M. W. Gates, J. Mottern, E. Murray, A. D. Molin, S. Triapitsyn, H. Baur, J. D. Pinto, S. van Noort, J. George & M. Yoder. 2013. A phylogenetic analysis of the megadiverse Chalcidoidea (Hymenoptera). Cladistics 29: 466–542.

Petrosia: The Sexual Life of the Sponges

It has to be admitted that sponges are not one of the best-publicised of animal groups. Even when they are given some grudging mention, there is little reference to the variety of sponges that can be found on our planet. But don't go thinking that all sponges are the same.

Stony sponge Petrosia ficiformis, copyright Véronique Lamare.

Petrosia is a genus of sponges found in tropical and subtropical oceans around the world. Members of this genus come in a variety of forms: branching, cylindrical, globular, lamellate or bowl-shaped. They may reach large sizes, with some species up to a metre or two in diameter, though others may be much smaller. Most species are dark colours such as red, brown or black, though the Sulawesi species Petrosia alfiani is a bright canary yellow (de Voogd & van Soest 2002). The reasons for classifying such superficially divergent forms in a single genus lie beneath the surface. However, it has a high proportion of skeletal spicules to soft tissue, giving Petrosia species a hard, brittle texture (hence they are sometimes known as 'stony sponges'). The spicules of Petrosia are mostly long, slightly curved rods that may be rounded or pointed at the ends; they may be large or smaller, with smaller spicules tending to be more common closer to the sponge's surface. Two subgenera are recognised within Petrosia on the basis of whether the spicules are mostly in a tangential (subgenus Petrosia) or reticulate (Strongylophora) arrangement. The subgenus Petrosia is known from the Atlantic and Pacific Oceans, whereas Strongylophora species are found in the Indian Ocean and the western Pacific (Desqueyroux-Faúndez & Valentine 2002).

Magnified view of surface of Petrosia ficiformis specimen, showing arrangement of spicules, from (Desqueyroux-Faúndez & Valentine (2002).

One of the best-studied species in this genus is the Mediterranean Petrosia ficiformis, which tends towards a cylindrical growth habit in sheltered spots. Like other sponges, P. ficiformis may provide an important habitat for other organisms. Smaller invertebrates live in and around the sponge, and molecular studies have shown that different sponge species tend to host their own distinct communities of bacteria. However, the niche provided by Petrosia in the Mediterranean can be vulnerable to damage: field observations have indicated that stony sponges grow exceedingly slowly. Maldonado & Riesgo (2009) found that in twenty years of diving off the Spanish coast, they saw almost no growth in individual sponges. When they took small (one by one-half centimetre) tissue samples from the sponges, it could take up to three months for the removed patch to regrow. Such a slow rate of growth definitely makes one wonder just how old some of the large Petrosia referred to above must be.

Bowl-shaped Petrosia lignosa, from de Voogd & van Soest (2002).

Maldonado & Riesgo (2009) were taking their samples to study how the sponges reproduced. Petrosia species are free spawners, releasing eggs and sperm directly into the water column. In the case of P. ficiformis, this happens in late autumn. Eggs develop at scattered locations through the sponge, but migrate within the body to form clusters before being released. The sexes are separate, with an individual sponge only producing either eggs or sperm. After fertilisation, the eggs develop into small ciliated larvae that may shift between a spherical and a multilobate form. Whereas the larvae of other sponges may be quite mobile, those of P. ficiformis are not active swimmers, presumably relying on the motion of water currents to carry them to a suitable resting spot. Maldonado & Riesgo (2009) noted that in the two years they observed Petrosia spawning, it occured at times when surge levels had risen immediately prior to the onset of stormy weather. Despite the regular associations of Petrosia with particular microbial populations, the larvae do not carry any sort of culture propagule from their parents, indicating that each individual sponge reacquires its associates from the surrounding waters. Larvae attach themselves to the substrate after two to four weeks of growth, and proceed to grow slowly (though, as is the way of sponges, if multiple larvae settle immediately adjacent to one another they may fuse into a single aggregate individual). Larvae grown in the lab took about one and a half months to develop distinct choanocyte chambers (the ciliated chambers in which a sponge filters water for food particles). They may share their environment with sea hares, but there is no question that Petrosia are sea tortoises.

REFERENCES

Desqueyroux-Faúndez, R., & C. Valentine. 2002. Family Petrosiidae van Soest, 1980. In: Hooper, J. N. A., & R. W. M. van Soest (eds) Systema Porifera: A guide to the classification of sponges pp. 906–917. Kluwer Academic/Plenum Publishers: New York.

Maldonado, M., & A. Riesgo. 2009. Gametogenesis, embryogenesis, and larval features of the oviparous sponge Petrosia ficiformis (Haplosclerida, Demospongiae). Marine Biology 156 (10): 2181–2197.

Voogd, N. J. de, & R. W. M. van Soest. 2002. Indonesian sponges of the genus Petrosia Vosmaer (Demospongiae: Haplosclerida). Zool. Med. Leiden 76 (16): 193–209.

Bizarre 'alien corpse' has idiots stumped

I know we've all become more familiar with 'mystery monster' corpse stories in the last few years, but I think they may have reached a new nadir. Fairfax featured a story today titled 'Bizarre 'alien corpse' discovered in Russia has experts stumped'. This is the corpse in question (image from linked article):

Supposedly, no-one (including a quoted 'biologist') has the slightest idea what this is, and the find has been sent off for extensive testing. Well, I don't know if I can claim to be any kind of expert myself, but even I can recognise the fricking Parrot of King Charles I when I see it.

Hypno-Moss

Recent decades have seen a great deal of shifting around in the classification of mosses. As molecular data have become de rigeur in phylogenetic studies, a number of features previously used to distinguish higher groupings have proven to be more labile than previously appreciated. This has lead to a hunt to discern whether other features may be more reliable.

Hypnum cupressiforme, from Andrew's Moss Site.

The Hypnales are one of the major moss groups: as currently recognised, about a third of mosses are Hypnales. They are a major subgroup of the clade of pleurocarpous mosses, i. e. those in which the reproductive sporophytes arise from the sides of gametophyte stems, as explained earlier in this post. In the past, the pleurocarpous mosses have been divided between three orders, the Hypnales, Hookeriales and Leucodontales, on the basis of features of branching habit and the peristome, the array of teeth surrounding the opening of the spore capsule. In the Hookeriales, the teeth of the endostome (the inner ring of the peristome) are connected by a high basal membrane, and molecular phylogenetic analyses have generally supported this order as monophyletic. The Leucodontales were defined by having reduced peristome teeth, and usually sympodial growth (as the primary shoot produces a side-branch, it ceases growing itself and the new branch becomes the new primary shoot). The Hypnales had well-developed peristome teeth, and their growth was generally monopodial (the primary shoot continues growing even after it produces side-branches). The distinction between these latter two orders also correlated with their choice of niches: Leucodontales were mostly epiphytes, whereas Hypnales mostly grew on the ground. However, molecular phylogenetic analyses have not supported the distinction between the Hypnales and Leucodontales, with features such as reduced peristome teeth apparently evolving multiple times with the united clade combining the two orders (Buck et al. 2000). As a result, recent authors have treated the Hypnales as including most members of both the prior orders Hypnales and Leucodontales. A smaller number of pleurocarpous mosses have been placed outside the clade including Hookeriales and Hypnales in the broad sense; there are now known as the Ptychomniales and Hypnodendrales. The broader Hypnales is less well defined morphologically, but its members tend to have differentiated alar cells (distinctly formed cells at the basal corners of the leaves) and smooth spore capsules (Huttunen et al. 2012).

A mat of Leucodon, from here.
This shuffling is not restricted to the higher levels, either. Relationships within the Hypnales remain poorly resolved; indications are that at some point this group went through a quite rapid diversification, resulting in a fairly high level of convergence between lineages and low support for molecular branches. Huttunen et al. (2012) found support for a large clade within the Hypnales including the majority of its Northern Hemisphere members, with a paraphyletic grade outside this containing mostly Southern Hemisphere taxa. Huttunen et al. suggested a Gondwanan origin for the Hypnales, with their diversification in the Northern Hemisphere (where the other pleurocarpous orders never made many inroads) related to the break-up of the Laurasian landmasses. Within the Northern Hemisphere clade, many previously recognised families appear to be polyphyletic; even the type genus of the order, Hypnum, contains species that seem to occupy widely separate places in the hypnalean family tree.

The Azores-endemic moss Echinodium renaudii, copyright Paulo A. V. Borges.

A good example of all this mess is the genus Echinodium, a small genus of six living species whose distinctive appearance lead to it being placed in a family all of its own. Echinodium species grow as fairly stiff plants with long leaves that taper to a narrow point and have thickened margins (the margins are two cell layers thick whereas the body of the leaf is only one cell thick). Echinodium mosses also have a very unusual distribution: two species are found in southeastern Australia and New Zealand, but the other four are restricted to the Macaronesian islands in the Atlantic (that is, the Canaries, the Azores and Madeira). When fossil Echinodium species were discovered in eastern Europe, it was suggested that the genus' current distribution could be a relict of a previously much wider one. However, a molecular analysis of the genus by Stech et al. (2008) identified another explanation: not only were the Australasian and Macaronesian Echinodium species widely separated geographically, they were widely separated phylogenetically. The Australasian species were placed in the family Neckeraceae, whereas the Macaronesian species were related to mosses of the family Lembophyllaceae. What is more, the Macaronesian species did not form a single clade within the Lembophyllaceae: at least one of the species was placed separately from the rest. The supposedly distinctive 'Echinodium' features, it seems, have evolved independently, possibly as an adaptation for wet habitats.

REFERENCES

Buck, W. R., B. Goffinet & A. J. Shaw. 2000. Testing morphological concepts of orders of pleurocarpous mosses (Bryophyta) using phylogenetic reconstructions based on trnL-trnF and rps4 sequences. Molecular Phylogenetics and Evolution 16(2): 180–198.

Huttunen, S., N. Bell, V. K. Bobrova, V. Buchbender, W. R. Buck, C. J. Cox, B. Goffinet, L. Hedenäs, B.-C. Ho, M. S. Ignatov, M. Krug, O. Kuznetsova, I. A. Milyutina, A. Newton, S. Olsson, L. Pokorny, J. A. Shaw, M. Stech, A. Troitsky, A. Vanderpoorten & D. Quandt. 2012. Disentangling knots of rapid evolution: origin and diversification of the moss order Hypnales. Journal of Bryology 34 (3): 187–211.

Stech, M., M. Sim-Sim, M. G. Esquível, S. Fontinha, R. Tangney, C. Lobo, R. Gabriel & D. Quandt. 2008. Explaining the ‘anomalous’ distribution of Echinodium (Bryopsida: Echinodiaceae): independent evolution in Macaronesia and Australasia. Organisms Diversity & Evolution 8 (4): 282–292.

Sea Bass, Mutant or Otherwise

...though to the best of my knowledge, none of them have fricking lasers on their heads.

Painted comber Serranus scriba, copyright Roberto Pillon.

The Serranidae are a group of marine fish that go by vernacular names such as sea bass, rock bass or rock cod. They are carnivores, and are found mostly around reefs in tropical and subtropical waters around the world. In appearance, they are fairly generalised (these are fish that look like fish) with a body shape that is longer than high, but not too long, and relatively big jaws with the lower jaw often jutting forward a bit beyond the upper. Some of them are quite colourful (as befits a tropical reef fish) and some of the smaller ones turn up in marine aquaria as a result. As used in the past, the Serranidae has been quite a broad grouping of fish united by having three spines on the margin of the opercle (the gill cover) and the maxilla in the upper jaw not hidden by the cheekbone when the mouth is closed. Members of this broad Serranidae were commonly divided between three subfamilies: the Serraninae (including the sea basses), Epinephelinae (including the groupers) and Anthiinae (basslets and goldies), though some authors further subdivided the Epinephelinae. However, recent molecular studies have indicated the polyphyly of this grouping, with the Serraninae and Epinephelinae occupying distinct positions within the clade known as the Serraniformes or Perciformes sensu stricto (see this old post), and so have cut the latter out of the Serranidae. As for the Anthiinae, their position remains uncertain, with some analyses placing them with the Serraninae and others with the Epinephelinae (Lautredou et al. 2013). As a result, a monophyletic Serranidae is probably to be restricted to the old 'Serraninae'.

Shy hamlet Hypoplectrus guttavarius, copyright Florent Charpin.

There are over eighty species listed for this restricted Serranidae on FishBase, but new ones continue to be described. As is common among reef fishes, it can be hard to determine exactly what counts as a species (whatever your preferred definition). A prime example of this is the genus Hypoplectrus, small serranids known as hamlets (no, I don't know why either) found in the Caribbean and the Gulf of Mexico. Hamlets come in a range of different colours and patterns, but structurally speaking the various forms are otherwise indistinguishable. As a result, some authors have regarded them as all colour morphs of a single species. Others have recognised close to twenty different species. Domeier (1994), conducting field observations on hamlets together with breeding experiments in the laboratory, found that different colour morphs would usually only mate with partners sharing their own colour pattern, though hybrid matings could be produced if no more suitable mate was provided. These hybrid matings produced offspring bearing intermediate colour patterns, and the rarity of such intermediates in the field led Domeier to infer that the different morphs were mostly acting as good species.

Kelp bass Paralabrax clathratus, photographed by Steve Lonhart.

Most sea basses are simultaneous hermaphrodites: they have both male and female reproductive organs functional at the same time. Though they are capable of fertilising their own eggs, they still usually breed in pairs with each individual alternating the release of male and female gametes. Not all serranids follow this reproductive template: members of the genera Chelidoperca and Centropristis are protogynous, starting their mature lives as females before switching over to males. Two species of Serranus, the lantern bass Serranus baldwini and the barred serrano S. psittacinus, are mostly simultaneous hermaphrodites like other species in the genus, but the largest individuals resorb their female organs and become exclusively males. Finally, many species of the genus Paralabrax have entirely separate males and females. Phylogenetic analysis suggests that protogyny may be the original mode of sexual development in the serranids, with separate sublineages developing simultaneous hermaphroditism vs separate sexes (Erisman & Hastings 2011). In correlation with this, individuals of Paralabrax that are functionally single-sexed have been found to retain non-functional remnants of the other sex's organs.

REFERENCES

Domeier, M. L. 1994. Speciation in the serranid fish Hypoplectrus. Bulletin of Marine Science 54 (1): 103–141.

Erisman, B. E., & P. A. Hastings. 2011. Evolutionary transitions in the sexual patterns of fishes: insights from a phylogenetic analysis of the seabasses (Teleostei: Serranidae). Copeia 2011 (3): 357-364.

Lautredou, A.-C., H. Motomura, C. Gallut, C. Ozouf-Costaz, C. Cruaud, G. Lecointre & A. Dettai. 2013. New nuclear markers and exploration of the relationships among Serraniformes (Acanthomorpha, Teleostei): the importance of working at multiple scales. Molecular Phylogenetics and Evolution 67: 140–155.

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.

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