Field of Science

Key Limpets

On two occasions before, I've presented you with members of the Fissurellidae, the keyhole and slit limpets. It's time for a return visit to the fissurellids, in the form of the diverse keyhole limpet genus Diodora.

Various views of shell of Diodora italica, copyright H. Zell.


Species have been assigned to Diodora from coastal waters pretty much around the world except for the coolest regions. They are small to moderate-size limpets, the largest species growing about three centimetres in length and two centimetres in height. The shell opens through a 'keyhole' at the apex through which the animal ejects waste matter and water that has been passed over the gills. The internal margin of this keyhole is surrounded by a callus on the underside of the shell; a distinguishing feature of Diodora is that this callus is posteriorly truncate. The external ornament of the shell is cancellate (arranged in a criss-cross pattern) and the margin of the shell is internally crenulated (Moore 1960). Moore (1960) listed three subgenera of Diodora distinguished by features of the keyhole shape and position but Herbert (1989) notes that these subgenera are not clearly distinct. A phylogenetic analysis of the fissurellids by Cunha et al. (2019) did recognise a clade including the majority of Diodora species analysed. However, species from the eastern Pacific formed a disjunct clade that may prove to warrant recognition as a separate genus.

As far as is known, Diodora species have a long lifespan, surviving for some ten to twenty years. They do not have a planktonic larva; young Diodora hatch directly from the egg as benthic crawlers. For the most part, they are presumed to graze on algae in the manner of other fissurellids and limpets. However, the northeastern Australian species D. galeata has been found feeding on the soft tissues of coral (Stella 2012), a habit that went unrecognised until fairly recently owing to the animal's cryptic nature, hiding deep among the branches of the host. Whether other Diodora species might exhibit similar lifestyles would require further investigation.

REFERENCES

Cunha, T. J., S. Lemer, P. Bouchet, Y. Kano & G. Giribet. 2019. Putting keyhole limpets on the map: phylogeny and biogeography of the globally distributed marine family Fissurellidae (Vetigastropoda, Mollusca). Molecular Phylogenetics and Evolution 135: 249–269.

Herbert, D. G. 1989. A remarkable new species of Diodora/i> Gray, 1821 from south-east Africa (Mollusca: Gastropoda: Fissurellidae). Annals of the Natal Museum 30: 173–176.

Moore, R. C. (ed.) 1960. Treatise on Invertebrate Paleontology pt I. Mollusca 1. Mollusca—general features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—general features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia. Geological Society of America, Inc. and University of Kansas Press.

Stella, J. S. 2012. Evidence of corallivory by the keyhole limpet Diodora galeata. Coral Reefs 31: 579.

Small Carpenters

It's time for another dip into the wide diversity of bees. The small carpenter bees of the tribe Ceratinini are small (often less than a centimetre in length), slender bees found on all continents except Antarctica, though their toehold in Australia is a very tenuous one indeed with only a single known species there. Though diverse, with hundreds of known species, the difficulty of breaking the tribe into clearly defined, monophyletic groups has lead recent authors to recognise a single genus Ceratina (Michener 2007). Distinctive subgroups previously treated as separate genera, such as the relatively large Megaceratina and the heavily punctate Ctenoceratina of Africa, and the both bright metallic and heavily punctate Pithitis of Africa and southern and eastern Asia, are now treated as subgenera. There are a lot of recognised subgenera, over twenty at last count, but there are also a lot of species not yet assigned to subgenus. Phylogenetic analysis of the ceratinins supports monophyly of most subgenera and a likely African origin for the clade as a whole, with multiple dispersals into Eurasia followed by a single dispersal to the Americas (Rehan & Schwarz 2015).

Ceratina sp., possibly C. smaragdula, copyright Vengolis.


Distinctive features of Ceratina compared to other bees include the absence of a pygidial plate, a flattened and hardened patch on the tip of the abdomen in females. As members of the family Apidae, Ceratina are long-tongued bees with a scopa (cluster of pollen-carrying hairs) on the hind legs, though the scopa does not enclose a bare patch for carrying a shaped pollen ball as in some other apids (for instance, the familiar honey bees). The scopa is less extensive in small carpenter bees than it is in other apids and the hairs on the body as a whole are rather short, so Ceratina look much shinier and less fuzzy than other bees. Ceratina are black or metallic green in colour (on rare occasions, the metasoma is red) and usually have yellow patches, particularly on the face.

Ceratina nest in a fennel stem, copyright Gideon Pisanty.


The name 'carpenter bee' refers to their practice of nesting in hollow stems or twigs, entered at broken ends. The absence of the pygidial plate is probably related to this manner of nesting: it is normally used by ground-nesting bees to tamp down soil when closing the nest. Most of the time, Ceratina are solitary nesters but two or more females may sometimes work on a nest together. In these cases, they adopt a proto-eusocial division of labour with one female laying eggs while the others act as 'workers' (I have no idea how they decide who gets to do what). Though a reduction in hairiness in bees is often associated with kleptoparasitism, no Ceratina species are known to behave in that manner (though some kleptoparasites are known among the members of the closely related and very similar tribe Allodapini). The reduction of the scopa may instead be associated with the bees carrying food supplies for the nest in their crop as well as on the legs. Cells are lined up in the nest stem with only simple partitions between them. These partitions are made from loose particles, mostly the pith of the stem, with no obvious adhesive holding them together. In at least some species, females will return to the nest after completion, dissembling and reassembling cell walls in order to clean out dead larvae and faeces that are then incorporated into the partitions. As such, while small carpenter bees are not directly on the evolutionary line leading to the more integrated colonies of the social bees, they do provide us with a model of what one stage in their evolution may have looked like.

REFERENCES

Michener, C. D. 2007. The Bees of the World 2nd ed. John Hopkins University Press: Baltimore.

Rehan, S., & M. Schwarz. 2015. A few steps forward and no steps back: long-distance dispersal patterns in small carpenter bees suggest major barriers to back-dispersal. Journal of Biogeography 42: 485–494.

Rove by the Riverside

The Staphylinidae, commonly known as the rove beetles, are one of the most diverse of the recognised beetle families. Indeed, thanks to their habit in recent years of glomming up lineages previously treated as distinct families like the pselaphids and scydmaenids, they now rival the weevils of the Curculionidae for the position of largest of all recognised animal families. But for their diversity and ubiquity, staphylinids are comparatively poorly studied, owing to a not-unwarranted reputation for taxonomic recalcitrance (the relatively soft bodies of many staphylinids mean they often do not handle well with standard methods for examining beetles). Perhaps the most neglected of all staphylinid subgroups is the subfamily Aleocharinae. Aleocharines are often minute (the average aleocharine is only a couple of millimetres in length) and their identification often requires resolving features that lie at the very limit of what can be seen with a standard dissecting microscope. Nevertheless, aleocharines are remarkably diverse and among their representatives are the representatives of the genus Parocyusa.

Parocyusa americana, from Brunke et al. (2012); scale bar = 1 mm.


Typical aleocharines have what is thought of as the 'standard' body form for staphylinids, with short, square elytra that do not cover the long, flexible abdomen (though I should mention that, with the aforementioned assimilation of the pselaphids and scydmaenids, I suspect there may now be more 'non-standard' staphylinid species than 'standard' ones). For the most part, they can be distinguished from other staphylinid subfamilies by the position of the antennae, with their insertions placed behind the level of the front of the eyes. Aleocharines are divided between numerous tribes; Parocyusa is included in the tribe Oxypodini, a heterogenous group of relatively unspecialised aleocharines. Notable features distinguishing Parocyusa from other aleocharine genera include legs with five segments to each tarsus, a frontal suture between the antennal insertions, the median segments of the antennae being longer than wide, the head not having a well defined 'neck', the sides of the pronotum not being strongly deflexed downwards (so the hypomeron, the lateral section of the pronotum, is clearly visible in side view), and deep transverse impressions across the third to fifth abdominal tergite but not across the sixth tergite or across the sternites (Newton et al. 2001). Members of the genus are a bit over three millimetres in length.

Species of Parocyusa are found widely in the Holarctic realm; I've found reference to species from Europe, Korea, and northeastern North America (I should also note that I've also encountered dark allusions to recent rearrangements of the generic status of some of these species but without access to such revisions I'm going to stick with what I can find). I haven't found any reference to their specific diet but I suspect that they would be micropredators, a common lifestyle for staphylinids of their kind. Parocyusa species are associated with running water, living among the gravel and sand alongside stream beds (e.g. Brunke et al. 2012). As such, these and other aleocharines have received attention in ecological studies: the higher the diversity of staphylinids present, the more healthy the ecosystem is likely to be.

REFERENCES

Brunke, A. J., J. Klimaszewski, J.-A. Dorval, C. Bourdon, S. M. Paiero & S. A. Marshall. 2012. New species and distributional records of Aleocharinae (Coleoptera, Staphylinidae) from Ontario, Canada, with a checklist of recorded species. ZooKeys 186: 119–206.

Newton, A. F., M. K. Thayer, J. S. Ashe & D. S. Chandler. 2001. Staphylinidae Latreille, 1802. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 272–418. CRC Press: Boca Raton.

Caloppiidae

The concept of ranks in taxonomy is ultimately an arbitrary one. There is no real definition of what constitutes an 'order', a 'family' or a 'subfamily'. What determines the rank that a given taxon is recognised at is a combination of tradition, convenience, and the taxon's relationships to other recognised taxa. As such, the question of whether a given classification is overly 'split' or 'lumped' is a meaningless one and arguing the point is a complete waste of time. That said, the classification of the 'higher' oribatid mites is massively oversplit.

A big part of the reason why oribatid classification seems such a mess, with large numbers of small families containing only a handful of genera and/or species apiece, can be attributed to simple ignorance. We simply do not have a good handle on how many oribatid taxa are related to each other and as a result we find ourselves with a great many orphan taxa still hunting for a good home. The Caloppiidae may be regarded as one such taxon.

Dorsal view of Luissubiasia microporosa, from Ermilov (2016). Scale bar = 100 µm; labels with 'A' indicate areae porosae.


Caloppiids are a pantropical group of about thirty species of poronotic oribatids (the group of oribatids exhibiting the octotaxic system, an arrangement of glandular openings on the notogaster), with three genera recognised in the family by Ermilov (2016): Zetorchella, Brassiella and Luissubiasia. Zetorchella, which includes the majority of the family's species, is also pantropical in distribution. Brassiella is known from the Indo-Pacific region and Liussubiasia is known from a single species from Cuba. Past authors have often referred to Zetorchella and the Caloppiidae by the names Chaunoproctus and Chaunoproctidae, respectively, but as the name Chaunoproctus had already had dibs called on it before the mite was named (by a bird, the now-extinct Bonin grosbeak Chaunoproctus ferreorostris), their respective most senior synonyms have to take over. Caloppiids are more or less egg-shaped in dorsal view. They lack the distinct pteromorphs of most other poronotics though they may have quadrangular projections in the humeral region (the 'shoulders'). The integument is usually heavily sculpted and foveate. The legs end in three claws apiece. The most characteristic feature of the group is that the openings of the octotaxic system on the notogaster, of which five pairs are present, are extremely small. The octotaxic system can take two forms, recessed saccules or porose patches. Those of caloppiids have usually been described as saccules but Ermilov (2016) states that, at least in some species, they are very small porose areas.

Going by their overall appearance, caloppiids are classified within the superfamily Oripodoidea. However, one of the most characteristic features of the Oripodoidea as an evolutionary group is that their nymphs have notogastral setae borne on individual off-centred sclerites (oribatid nymphs often look very different from their adults and are often more soft-bodied). At this point in time, we simply do not know what the nymphs of caloppiids look like so we cannot say whether they possess this crucial feature. Conversely, with their lack of pteromorphs, caloppiids bear a distinct similarity to the more diverse oripodoid family Oribatulidae. The two families have mostly been separated on the basis of caloppiids supposedly having an octotaxic system of saccules rather than porose areas, a distinction that I've already noted may not hold up. There's also something of an open question whether the distinction between saccules and porose areas is really as significant as it has been thought in the past. So, at present, we can't say with confidence whether caloppiids are true oripodoids... or whether they are not only oripodoids but don't even warrant recognition as a distinct family from oribatulids.

REFERENCE

Ermilov, S. G. 2016. Luissubiasia microporosa gen. nov., sp. nov. (Acari, Oribatida, Caloppiidae) from Cuba. International Journal of Acarology 42 (2): 127–134.

The Grisons

Spend a bit of time following discussions of nature documentaries and other popular representations of biodiversity, and one topic you're likely to see come up is the biases that tend to exist in what gets represented. Images from eastern and southern Africa predominate while the west and north of that continent get overlooked. Europe and North America receive much more attention than the temperate regions of Asia. Another region whose diversity tends to go underrepresented is South America. The casual observer might think this continent is all monkeys and jaguars but South America is also home to notable radiations of dogs, deer, rodents, and other animals that many people would associate more with other parts of the world. Among these overlooked elements of the South American fauna are the local species of mustelid, including the grisons of the genus Galictis.

Greater grison Galictis vittata, copyright Tony Hisgett.


Grisons are somewhat ferret- or skunk-like animals found across almost the entirety of South America, and north into southern Mexico. They are greyish in colour dorsally (the name 'grison' itself means 'grey') with a black face and underparts. A pale stripe separates the upper and lower parts across the top of the face and continues diagonally back to the shoulders. They feed on small vertebrates and tend to be solitary hunters though they may sometimes form small family groups. They are primarily terrestrial and diurnal in habits. They have a reputation for ferocity; residents of Chile apparently have a history of using comparisons to grisons to describe unchecked rage (Yensen & Tarifa 2003b), in a similar manner to references to wolverines and honey badgers in other parts of the world. Contrasting colour patterns like those of the grisons are associated in other musteloids (such as skunks) with the production of offensive odours for defence, and grisons also produce strong-smelling secretions from their anal glands. Though some sources have claimed the odour produced by the lesser grison to be worse than a skunk's, it appears that these reports are exaggerated (Yensen & Tarifa 2003b).

Lesser grison Galictis cuja, copyright Ken Erickson.


Most authors have recognised two species of grison, the greater grison Galictis vittata and the lesser grison G. cuja*, as corroborated by a recent taxonomic study of the genus by Bornholdt et al. (2013). As their names indicate, the greater grison is generally larger and more robust than the lesser, being about 60 to 76 cm in total length versus 44 to 68 cm for the lesser grison (Yensen & Tarifa 2003b). The tail is also proportionately shorter in the greater grison (30% of the total length for the greater, 40% for the shorter). Fur is relatively longer and denser in the lesser grison, giving it more of a fluffy look. Whereas the dorsal fur is always a plain grey in the greater grison, it may often have a yellowish tinge in the lesser (not always, though). The two are generally distinct in range and habitat, as well. The greater grison is an animal of tropical forests and inhabits the northern part of the genus' range in Central America and northern and western South America. The lesser grison inhabits drier habitats, in arid or temperate regions, and so occupies the southern and eastern parts of the continent. The ranges of the species are known to overlap in Bolivian and Paraguay where their respective biomes approach each other.

*Some sources have listed a third species G. allamandi but this seems have been something of a 'ghost' taxon born from confusion whether the name 'G. vittata' applied to the greater or lesser species.

The genus Galictis arrived in South America as part of the Great American Biotic Interchange, about three million years ago. The general consensus is that it is derived from the genus Trigonictis of the North American Pliocene. Indeed, it has even been suggested that the two North American species of Trigonictis might represent independent ancestors of Galictis, with the larger T. macrodon giving rise to the greater grison and the smaller T. cookii birthing the lesser grison (Yensen & Tarifa 2003a). This certainly would seem overly complicated, though, and molecular data are more in line with a more recent separation of the species.

REFERENCES

Bornholdt, R., K. Helgen, K.-P. Koepfli, L. Oliveira, M. Lucherini & E. Eizirik. 2013. Taxonomic revision of the genus Galictis (Carnivora: Mustelidae): species delimitation, morphological diagnosis, and refined mapping of geographical distribution. Zoological Journal of the Linnean Society 167: 449–472.

Yensen, E., & T. Tarifa. 2003a. Galictis vittata. Mammalian Species 727: 1–8.

Yensen, E., & T. Tarifa. 2003b. Galictis cuja. Mammalian Species 728: 1–8.

Nocardia pseudovaccinii

As noted on this site before, the Actinobacteria are one of the most significant groups of bacteria in the terrestrial environment. Among the more diverse genera of Actinobacteria is Nocardia, members of which produce fine, branching mycelia that often fragment into individual rod-shaped or coccoid segments, each of which is capable of developing into a new mycelium (Goodfellow et al. 2012). As is the way of things, Nocardia species are usually soil dwellers but are more commonly studied as facultative pathogens. Nevertheless, recent years have seen the recognition of an increasing number of species isolated from soil samples with one such species being Nocardia pseudovaccinii.

Nocardia pseudovaccinii was described as a new species by Kim et al. (2002). In culture, N. pseudovaccinii grows a beige-red substrate mycelium supported a scarce, white aerial mycelium. Kim et al. (2002) identified the species as able to utilise a wide range of organic substrates such as ribose and glucosaminic acid though it could not break down others such as sucrose or citrate. Molecular analyses of Nocardia in Kim et al. (2002) and Goodfellow et al. (2012) do not really indicate a clear association of N. pseudovaccinii with any other species. Bacterial systematists apparently still maintain that neighbour-joining analyses are something more than a complete waste of time. I do not support this view.

The strains assigned to N. pseudovaccinii by Kim et al. (2002) had previously been identified as another species, N. vaccinii, hence the new species' name ('vaccinii', in case you were wondering, has no direct connection to vaccines but refers to Vaccinium, the plant genus including blueberries and from which N. vaccinii was first isolated). Nocardia vaccinii has been known to act as a facultative plant pathogen but I am not aware of this role being identified for N. pseudovaccinii. The original isolates were cultured from soil (though Kim et al. say nothing about what kind of soil or even where it was sampled). Nocardia pseudovaccinii has also been found forming part of the microbiome of wireworms of the genus Agriotes, beetle larvae that feed on plant roots. It may form a symbiotic association with these grubs that provides the latter with antibiotic protection from the pathogenic fungus Metarhizium brunneum (Kabaluk et al. 2017). A good thing for the wireworms but perhaps not so good for agriculturists who would like to keep them under control.

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.

Kabaluk, T., E. Li-Leger & S. Nam. 2017. Metarhizium brunneum—an enzootic wireworm disease and evidence for its suppression by bacterial symbionts. Journal of Invertebrate Pathology 150: 82–87.

Kim, K. K., A. Roth, S. Andrees, S. T. Lee & R. M. Kroppenstedt. 2002. Nocardia pseudovaccinii sp. nov. International Journal of Systematic and Evolutionary Microbiology 52: 1825–1829.

Pyrgoidae

I have referred in the past to there being something of a divide in approaches to the classification of the Foraminifera. This divide arises from disagreements such as the relative significance of various character complexes. One taxon that stands as an example of such disagreements is the subject of this post, the family Pyrgoidae as recognised by Mikhalevich (2005).

Pyrgo williamsoni, copyright Michael.


Pyrgoids are members of the group of forams generally recognised as the Miliolida, the porcelaneous forams. In this group, the wall of the test is composed of calcite but the calcite crystals are not regularly lined up with each other so the wall is not transparent. As a result, the wall of the test resembles porcelain in appearance. Most miliolidans have the chambers of the test coiling in a single plane. The Pyrgoidae were distinguished from other miliolidans by Mikhalevich (2005) by the overall structure of the test which is primarily biloculine (with the whorls of the test composed of two chambers). The family was divided into subfamilies by the nature of the test aperture: single with an inner tooth in Pyrgoinae, single with a flap in Biloculinellinae, and multiple (at least when mature) in Cribropyrgoinae and Idalininae. Idalininae also differed from other subfamilies in that the very last chamber was further enlarged to envelop the entire test. Members of the Pyrgoidae are known from the fossil record going back to the Jurassic period.

In the system of Loeblich & Tappan (1964), however, the pyrgoids were not recognised as a single group. Instead, they were dispersed among separate subfamilies of the family Miliolidae. Part of the reason was simply that Loeblich & Tappan did not divide the miliolidan families as finely as Mikhalevich later would but a bigger difference was one of priority. Loeblich & Tappan regarded the nature as an aperture as a more important feature taxonomically than the arrangement of chambers. Both classifications seem to have been constructed more from a diagnostic viewpoint than necessarily intended to reflect phylogenetic relationships.

Cribropyrgo aspergillum, from the National Museum of Natural History.


As with most other forams, pyrgoids exist in what are called megalosphaeric and microsphaeric forms. These forms represent alternate generations in the foram life cycle: microsphaeric forams are the sexually reproducing generation whereas megalosphaeric forams reproduce asexually. The names refer not to the overall size of the individuals but to the size of the proloculus, the very first embryonic chamber that sits at the center of the test. In megalosphaeric pyrgoids, the developing test is biloculine from the very start. In microsphaeric individuals, the earliest stages of the test are quinqueloculine (with five chambers per whorl) then become triloculine then finally biloculine (with a further progression for the idalinines, of course). The significance of the differences between the two forms has historically been the subject of discussion with some authors arguing that the microsphaeric forms represented a retention and overwriting of ancestral forms, or an expression of the trajectory the lineage might evolve along in the future (Loeblich & Tappan 1964). The most likely explanation, though, seems to me to be the simplest. The size of the proloculus correlates with the amount of cytoplasm in the young foram. Megalosphaeric pyrgoids start with fewer chambers per volution from the start for the simple reason that they don't have the space to pack in more.

REFERENCES

Loeblich, A. R., Jr, & H. Tappan. 1964. Treatise on Invertebrate Paleontology pt C. Protista 2. Sarcodina: chiefly "thecamoebians" and Foraminiferida vol. 1. The Geological Society of America, and The University of Kansas Press.

Mikhalevich, V. 2005. The new system of the superfamily Quinqueloculinoidea Cushman, 1917 (Foraminifera). Acta Palaeontologica Romaniae 5: 303–310.

Donaldina: Palaeozoic Turrets

Within the last few decades, we've developed a reasonably good idea of what are the primary subdivisions of gastropods alive today. One such generally accepted lineage is the Heterobranchia (or, depending on the author, the Heterostropha), a group that includes (among others) the air-breathing pulmonates as well as the marine sea slugs and bubble shells. In the fossil record, the roots of this lineage extend well back into the Palaeozoic with early members recognisable by their distinctive mode of shell development. The larval shell, the protoconch, of these forms spirals in the opposite direction from the mature teleoconch, so the animal will start its life sinistral (spiralling left) and end it dextral (spiralling right; if you're having difficulty imagining how this works, the protoconch often ends up sitting upside down relative to the teleoconch). Among the earliest heterobranchs in the fossil record is the genus Donaldina.

Specimen of Donaldina (1.2 mm in height), with close-up of protoconch, from Bandel et al. (2002).


Fossils of Donaldina have been found around the world and the genus persisted for a long time. The earliest potential Donaldina have been described from the Early Devonian but their inclusion in the genus is uncertain (Bandel et al. 2002). The protoconch on these early forms is poorly preserved and it is uncertain whether they truly showed a heterobranch development. The genus was definitely present by the early Carboniferous and persisted into the lower Permian. This is an impressive length of time: the Carboniferous alone last for around sixty million years.

Donaldina was a genus of small, high-spired gastropods, less than a centimetre in height. Many early members of the Caenogastropoda, the likely sister group of the Heterobranchia, also had shells of this kind and it may have represented the ancestral form for the two lineages. The sinistral protoconch of Donaldina was almost planispiral (spiralling in a flat plane) and completed between one and two whorls. The multi-whorled, dextral teleoconch was characterised by an ornament of spiral cords, usually only on the lower half of the whorl.

So what were Donaldina doing with their time when alive? Modern high-spired gastropods occupy a range of lifestyles, including free-living grazers, burrowers, or sedentary forms that live as filter feeders or parasites of other animals (Signor 1982). The morphology of Donaldina suggests that it is unlikely to be a burrower. The whorls are individually rounded whereas those of habitual burrowers tend to be flattened so the shell moves more smoothly through the sediment. The ornamentation on the underside of the whorl would presumably also have presented resistance to burrowing. The shape of the aperture in Donaldina is more suggestive of a free roamer, as a sinus in the upper part of the outer margin would have allowed the animal to pull back into its shell while the plane of the aperture was held as flat as possible against the substrate to protect against predators. Overall, the lifestyle of Donaldina may not have been dissimilar to that of the modern mudsnails of Cerithium and similar genera, crawling about in search of algae and other tasty morsels.

REFERENCES

Bandel, K., A. Nützel & T. E. Yancey. 2002. Larval shells and shell microstructures of exceptionally well-preserved Late Carboniferous gastropods from the Buckhorn Asphalt Deposit (Oklahoma, USA). Senckenbergiana Lethaea 82 (2): 639–689.

Signor, P. W., III. 1982. Resolution of life habits using multiple morphologic criteria: shell form and life-mode in turritelliform gastropods. Paleobiology 8 (4): 378–388.

Mooching Off the Relatives

Something I've referred to before but only (I think) in passing is that, among the enormous diversity of bees that inhabit this world, there are a large number of species that act as cleptoparasites*. That is, instead of constructing and provisioning their own nests, they lay their eggs in the nests of other bee species. When the eggs hatch, the emerging larvae feed on the provisions that the constructing bee intended for her own offspring. One lineage of these cleptoparasites is the megachilid genus Coelioxys.

*Depending on the source, you may see this term spelt as either 'cleptoparasite' or 'kleptoparasite'. Personally, I've never been able to decide just which I should be using.

Coelioxys sodalis, copyright jgibbs.


Coelioxys is a diverse, cosmopolitan genus with nearly 500 known species, closely related to the even more diverse leafcutter bees and resin bees of the genus Megachile. Species vary in size from half a centimetre to nearly an inch in length. They are fairly similar to species of Megachile in overall appearance, the most obvious difference being that (as with most cleptoparasitic bees) their covering of hair is greatly reduced. In particular, the dense scopa of hairs that covers the underside of the metasoma in female Megachile is absent. The primary function of the hairs in bees is to carry pollen; with no nest of their own to worry about, cleptoparasitic bees have no need for such dense hairs. Coelioxys females also differ from Megachile in the shape of the metasoma which is tapering and ends in a narrow tip. More on that in a moment.

As might be expected for such a large genus, Coelioxys has been divided between a number of subgenera. Until recently, the definitions of a number of these subgenera was somewhat uncertain. The biggest problem was that most revisions of the genus had been done on a regional level so (for instance) North American taxa were more finely subdivided than in the Old World. However, a recent phylogenetic analysis of the genus by da Rocha Filho & Packer (2017) redefined a number of subgenera and adjusted their definitions. For instance, the type subgenus Coelioxys, recognised as subcosmopolitan by Michener (2007), became restricted to just two species, the European C. quadridentata and the North American C. sodalis. Whereas Michener's concept of Coelioxys was essentially recognised by lacking the specialised features of other subgenera, the restricted Coelioxys sensu stricto can be recognised by having the outer margin of the pronotal lobe conspicuously rounded, as well as having the pilosity on the mesosoma suberect, long and thin, without spots of appressed hairs (da Rocha Filho & Packer 2017).

For the most part, Coelioxys species are cleptoparasites of Megachile though some have also been found mooching off Apidae species. Coelioxys quadridentata, for instance, has been found in association with nests of both Megachile and Anthophora. In most cases, a female Coelioxys will lay into a host nest before it is closed, while the constructor is away foraging for supplies. The narrow metasoma allows the Coelioxys to reach into the cavity containing the nest and insert her eggs into the nest wall where the host will not notice it. Often, multiple eggs will be laid in a single nest. After the nest is closed, the eggs hatch into larvae that look fairly unremarkable for their first one or two instars: like other bee larvae, not doing much more than sit there and eat. But upon reaching the second or third instar, the Coelioxys larva develops greatly enlarged mandibles that it uses to stir through the nest's food mass and execute any other larvae and eggs contained therein. Both the original host larva and any other Coelioxys larvae the nest may contain are dealt with in this manner (presumably the process of finding an appropriate host nest is difficult enough that the waste of eggs is still worth it for the parent Coelioxys to increase the chance that at least one reaches maturity). Its competitors thus removed, the larva them moults back to a more average form with nothing more agin to do but eat until the time to mature is reached.

REFERENCES

Michener, C. D. 2007. The Bees of the World 2nd ed. John Hopkins University Press: Baltimore.

Rocha Filho, L. C. da, & L. Packer. 2017. Phylogeny of the cleptoparasitic Megachilini genera Coelioxys and Radoszkowskiana, with the description of six new subgenera in Coelioxys (Hymenoptera: Megachilidae). Zoological Journal of the Linnean Society 180: 354–413.

The Barrington Tops Stag Beetle

The stag beetles of the Lucanidae are among the most dramatic of all beetles. They are large, glossy, and the adult males often have greatly enlarged mandibles that are used in conflict with other males. As larvae, lucanids are found feeding on rotting wood; adults may feed on nectar and are largely nocturnal. Australia is home to its share of lucanid diversity though the need for suitable food for larvae means that they are mostly restricted to damper regions of the country. As a result, many Australian stag beetles have limited ranges, rendering them vulnerable if not (in this time of rising temperatures and reduced rainfalls) actively endangered. One such species is the Barrington stag beetle Lissapterus tetrops.

Female (left) and major male Lissapterus tetrops, from Coleptera7777.


The Barrington Tops is a mountain range forming part of the Great Dividing Range in New South Wales, direct north from Newcastle. The Barrington stag beetle was described from this range in 1916 by Arthur Lea, one of Australia's most prolific coleopterologists, and is restricted to rain forests at the upper heights of the range. Lissapterus is an endemic Australian genus of flightless stag beetles distinguished from other members of the family by the shape of the antennae. The terminal club that is usually characteristic of the antennae of stag beetles is less defined in Lissapterus with the last few segments of the short antennae being little larger than the rest. Like most other species in the genus, L. tetrops is almost entirely black, only becoming slightly reddish on the legs and antennae. It grows about an inch in length, males and females being not that dissimilar in size. Lissapterus tetrops differs from other species in the genus in lacking foveae on the pronotum and (mostly) on the head, being relatively sparsely punctate dorsally, and having the eye completely divided by a canthus. Major males have long curved mandibles with a pair of teeth internally near the midpoint, placed one above the other. Minor males and females have much smaller, more ordinary looking mandibles.

The natural history of this species is little known but it presumably resembles that of other species in the genus. Adults are found under rotting logs partially buried in the forest floor that provide food for the larvae. Adults may live for a long time, potentially up to about a year, though it is unclear what exactly they feed on. Other species of Lissapterus are mostly found in disjunct locations up and down the Great Dividing Range, their populations presumably becoming separated as the warming and drying of Australia's climate as it moved northwards forced them out of the lowlands. As the climate continues to become warmer and drier, these beetles may find themselves having to retreat higher and higher, and eventually they may find themselves with no further to go.

REFERENCE

Lea, A. M. 1916. Notes on some miscellaneous Coleoptera, with descriptions of new species. Part II. Transactions of the Royal Society of South Australia 40: 272–436, pls 32–39.

Oribatid Time Again

The oribatid mite genus Neogymnobates was first recognised from Illinois in 1917. Since then, the genus has been found to be more widespread in North America and has also been described from Korea and Tibet. Species of Neogymnobates are known from arboreal habitats or in association with fallen wood, and live as grazers of micro-vegetation such as lichens.

Neogymnobates luteus, copyright Monica Young.


Neogymnobates belongs to the Ceratozetidae, a diverse family of oribatids whose characteristic features include a tutorium (a projecting tooth-like structure) on the side of the prodorsum and immovable pteromorphs on either side of the front of the notogaster. Neogymnobates has the lamellae on either side of the prodorsum widely separated from each other and connected by a transverse translamella at the front. There are thirteen pairs of setae on the notogaster and four pairs of porose areas (Balogh & Balogh 1992). One species, N. marilynae of British Columbia and Washington State, is known to have an extra unpaired porose area on the midline near the rear of the notogaster (Behan-Pelletier 2000), an unusual feature among oribatids but one whose significance is uncertain). Their legs end in three claws, a feature that (as I've commented before) correlates with their arboreal habits.

Half a dozen species of Neogymnobates have been recognised to date (Subías 2004). The species are distinguished by features such as the size and appearance of the setae, and the development of the prodorsal lamellae and translamella. One Korean species, N. parvisetiger, has been awarded its own subgenus Koreozetes due to its particularly small, almost indiscernable notogastral setae and its anteriorly notched rather than rounded rostrum (Aoki 1974). Most species are only known from limited ranges except one, N. luteus, for which separate subspecies have been recognised in northern North America and in Korea. Rather unexpectedly, this last species has also recently been recorded from Zanzibar (Ermilov & Khaustov 2018). This is a remarkable range increase, both geographically and ecologically (enough so that I can't help feeling it would benefit from double-checking) that raises the possibility that we may yet have a lot to learn about this oribatid genus.

REFERENCES

Aoki, J. 1974. Oribatid mites from Korea. I. Acta Zoologica Academiae Scientiarum Hungaricae 20 (3–4): 233–241.

Balogh, J., & P. Balogh. 1992. The Oribatid Mites Genera of the World vol. 1. Hungarian Natural History Museum: Budapest.

Behan-Pelletier, V. M. 2000. Ceratozetidae (Acari: Oribatida) of arboreal habitats. Canadian Entomologist 132: 153–182.

Ermilov, S. G., & A. A. Khaustov. 2018. A contribution to the knowledge of oribatid mites (Acari, Oribatida) of Zanzibar. Acarina 26 (2): 151–159.

Subías, L. S. 2004. Listado sistemático, sinonímico y biogeográfico de los ácaros oribátidos (Acariformes, Oribatida) del mundo (1758–2002). Graellsia 60 (número extraordinario): 3–305.

Predators of the European Eocene

Among mammals in today's modern fauna, the role of terrestrial carnivore is dominated by members of one particular lineage, known (appropriately enough) as the Carnivora. But travel back in time to the Eocene period, roughly 56 to 34 million years ago, and you'll find a range of now extinct groups sharing that role. This post is looking at one of those groups, the proviverrines.

The Proviverrinae are a subgroup of the Hyaenodontidae, one of the two families of carnivores commonly associated as the creodonts. I've discussed creodonts before, and the overhanging question of whether they form a coherent evolutionary group. Currently, my impression is that most mammal palaeontologists seem inclined to think that hyaenodontids and oxyaenids probably do not share an immediate common ancestry. However, nor is there any clear idea of what else either group may relate to.

Skull of Cynohyaenodon cayluxi, photographed by Ghedoghedo.


Historically, proviverrines have been treated as the basal grade from which other groups of hyaenodontids were derived with representatives known from Europe and North America. However, a phylogenetic analysis of early hyaenodontids by Solé (2013) lead to a division of the 'proviverrines' between three monophyletic subfamilies: the Proviverrinae proper, the Sinopinae and the Arfiinae. Under this system, the Proviverrinae are a uniquely European group. As is standard in mammalian palaeontology, proviverrines (in the strict sense) are distinguished from other hyaenodontids by features of the teeth. Notable among these is the presence of a double root on the first lower premolar of most proviverrines; other hyaenodontids have a single root on this tooth.

The earliest proviverrines are known from the very beginning of the Eocene (Solé et al. 2014). Current thinking is that their ancestors probably immigrated into Europe around this time from Africa. The Late Paleocene Tinerhodon disputatum from northern Africa resembles a proviverrine in overall appearance but was probably more basally placed in respect to hyaenodontids as a whole. The name 'Proviverra' can be read as 'early civet' and while proviverrines were not related to modern civets (which are, of course, true carnivorans) this is probably not a bad indication of the overall appearance of their original appearance. These were very small animals, probably less than 100 g in body weight, and probably had a fairly generalised diet of small vertebrates and invertebrates. At first, proviverrines seem to have been restricted to southern Europe, what is now Spain and the very southernmost part of France. Northern Europe was inhabited by the Arfiinae and Sinopinae, as well as species of Oxyaenidae (the other 'creodont' family). Sinopinae were also found in southern Europe and may have excluded the proviverrines from evolving larger size. However, the other hyaenodontids and oxyaenids went extinct in Europe not to long after the beginning of the Eocene. A turnover in the mammalian fauna of North America around this time appears to be due to a cooling of the climate; though the evidence for climate cooling is less clear in Europe, it seems reasonable that it was going through similar changes. With their competitors out of the picture, the proviverrines rapidly diversified into the regions and niches that had been left unoccupied.

Lesmesodon edingeri, photographed by Ghedoghedo.


The largest proviverrines, members of the genera Prodissopsalis, Paenoxyaenoides and Matthodon, would eventually reach weights of close to twenty kilograms, about as large as a medium-sized dog. They would also diversify in their habits. Members of the genera Oxyaenoides and Paenoxyaenoides were cursorial hypercarnivores, their dentition specialised for a diet almost exclusively of meat*, like that of a modern cat. Matthodon and Quercytherium, in contrast, were genera whose dentition showed more adaptations for cracking hard materials such as bone. They may have had lifestyles more like those of hyaenas, with Matthodon (which combined adaptations for hypercarnivory and bone-cracking) perhaps being more of an active hunter than Quercytherium.

*These two genera also provide an excellent example of the role of convergent evolution in the evolution of mammalian carnivores. Their appearance to other hypercarnivorous hyaenodontids was such that it was only recently that they were recognised as proviverrines rather than members of other subfamilies no longer thought to have been found in Europe. And not only are they remarkably convergent on other subfamilies, the phylogenetic analysis of proviverrines by Solé et al. (2014) suggests that they're not even directly related to each other within that clade.

Proviverrines remained the dominant mammalian carnivores in Europe for about the next twenty million years but then went into a sharp decline. This reversal of fortunes may have been due to the increasingly cool, dry conditions developing at this time, and/or it may have been related to competition from the first true carnivorans arriving in Europe. The larger, more specialised proviverrines disappeared rapidly when their time came. The last surviving genus, Allopterodon, was a small form, little more than one kilogram in weight, and had a generalised dentition indicating a relatively unspecialised diet. This may have been a return to something like the lineage's original form but it would not save it: by the end of the Eocene, the proviverrines would be completely extinct.

REFERENCES

Solé, F. 2013. New proviverrine genus from the Early Eocene of Europe and the first phylogeny of Late Palaeocene–Middle Eocene hyaenodontidans (Mammalia). Journal of Systematic Palaeontology 11 (4): 375–398.

Solé, F., J. Falconnet & L. Yves. 2014. New proviverrines (Hyaenodontida) from the early Eocene of Europe; phylogeny and ecological evolution of the Proviverrinae. Zoological Journal of the Linnean Society 171: 878–917.

Anabaena

Way back in the day, back when blogging was actually a thing that people paid a modicum of attention to (as opposed to its current status as a way for old fogies to scream into the void), I used to have a link to this blog at some indexing/promotional site that advertised its coverage as including, among other things, "multicellular bacteria". Now, when one is considering micro-organisms, the line between 'multicellular' and 'colonial' is a vague one. Nevertheless, there are certain lineages of colonial bacteria in which individual cells within the colony may become differentiated in a way that renders them incapable of surviving on their own. A definite argument could therefore be made that such colonies have crossed the boundary into true multicellularity.

Light microscopy image of Anabaena circinalis at 400–600×, copyright Imre Oldal. The lighter coloured cells are heterocysts.


A particularly diverse such bacterial lineage is the heterocyst-forming members of the Cyanobacteria, the blue-green algae, of which the genus Anabaena is a widespread representative. Anabaena species grow as long strings of cells referred to as trichomes. These trichomes are often embedded within a layer of dense mucilage though Anabaena species lack the hard external sheath produced by some other cyanobacterial genera. The cells within a trichome are more or less spherical, cylindrical or barrel-shaped and are not differentiated from each other in such a way that a trichome could be said to have a 'base' or 'apex'. Trichomes may be planktonic or benthic, depending on the species. Benthic species are capable of slow movement and the cells at each end of a trichome are conical in shape. Planktonic species are immobile; the cells contain gas vesicles to provide buoyancy and those at the ends of the trichomes are not differentiated from the remainder (Boone et al. 2001).

The aforementioned heterocysts are specialised cells within the trichome of Anabaena species and related Cyanobacteria that are capable of fixing molecular nitrogen from the surrounding environment (trichomes growing in a medium providing a surfeit of previously fixed nitrogen will not produce heterocysts). The enzymes responsible for nitrogen fixation require the absence of oxygen to function and so heterocysts devlop a thick, multi-layered envelope outside the original cell wall. They also lose the capacity to conduct their own photosynthesis. As a result, the heterocyst becomes completely dependent on the surrounding cells in the trichome for the production of carbohydrates, supplying them in turn with nitrogen incorporated into amino acids (Golden & Yoon 2003). Anabaena species will generally have individual heterocysts separated by about ten to twenty photosynthetic cells; the heterocysts are most commonly at internal positions within the trichome though they may occasionally occupy a terminal position. One species usually included in Anabaena, A. azollae, lives in close association with the small, floating aquatic ferns of the genus Azolla. Anabaena azollae trichomes are contained within cavities on the underside of the leaves. Heterocyst formation is much more extensive than in free-living Anabaena with fully 20–30% of the cells being heterocysts. Developing sporocarps on the Azolla also become infested with A. azollae akinetes (thick-walled cells that act as resting spores) that are picked up by emerging embryos so the symbiont is transmitted down through the generations (Peters 1989). Because of this association, Azolla growth is often encouraged as a source of nitrogen for crops grown in water such as rice. Other Anabaena species, conversely, are less welcomed by humans due to their production of harmful toxins.

The advent of molecular studies of bacterial phylogeny has confirmed the integrity of the heterocyst-formers as a monophyletic lineage within the Cyanobacteria. However, the internal classification of this clade is far more uncertain. Though well recognised from a morphological standpoint, molecular studies have questioned whether the genus should continue to be recognised in its current form. A study by Gugger et al. (2002) comparing planktonic strains of Anabaena with another genus Aphanizomenon, distinguished by differences in cell and trichome shape, found that the two were well and truly intermingled genetically. Some of the features hitherto used in cyanobacterial classification may be affected by the environment. For instance, Anabaena azollae will, under certain conditions, produce hormogonia, small, motile chunks of trichome that function as disseminules. Hormogonia production is supposed to be a feature of another cyanobacterial genus, Nostoc, rather than Anabaena (and it is worth noting that other Cyanobacteria involved in symbioses with plants have been assigned to Nostoc) (Peters 1989). There is a need out there for an extensive investigation into the relationships of these genera, and maybe a thorough re-analysis of their definitions.

REFERENCES

Boone, D. R., R. W. Castenholz & G. M. Garrity (eds) 2001. Bergey’s Manual of Systematic Bacteriology 2nd ed. vol. 1. The Archaea and the Deeply Branching and Phototrophic Bacteria. Springer.

Golden, J. W., & H.-S. Yoon. 2003. Heterocyst development in Anabaena. Current Opinion in Microbiology 6: 557–563.

Gugger, M., C. Lyra, P. Henriksen, A. Couté, J.-F. Humbert & K. Sivonen. 2002. Phylogenetic comparison of the cyanobacterial genera Anabaena and Aphanizomenon. International Journal of Systematic and Evolutionary Microbiology 52: 1867–1880.

Peters, G. A., & J. C. Meeks. 1989. The Azolla-Anabaena symbiosis: basic biology. Annual Review of Plant Physiology and Plant Molecular Biology 40: 193–210.

Algal Intrafamilial Strife

Most of you are probably familiar with the old adage that one should keep one's friends close and one's enemies closer. From a phylogenetic perspective, the red algal genus Plocamium has certainly achieved the latter.

Plocamium species growing on the coast of South Africa, copyright Derek Keats.


Plocamiaceae is a cosmopolitan family of marine red algae found mostly in temperate waters. They may grow in a variety of habitats from sheltered to exposed. Phylogenetic analyses have indicated that the family is somewhat distantly related to other red algal families, such that it is currently classified in its own order (Saunders & Kraft 1994). The great majority of the forty-odd known species of Plocamiaceae are currently placed in the genus Plocamium. These are reasonably sized seaweeds with erect or decumbent thalli that can grow about half a metre in length/height. They have flattened, complanately branched axes (that is, the branches are in the same plane as the axis they branch from). Branching is pectinate (comb-like) with each axis producing usually between two and six branchlets. The lower branchlets in a series are usually unbranched but higher ones will produce their own series of side-branchlets. In particular, the last branchlet will generally grow and overtop the axis it arose from to effectively replace it (as a result, the axis of the algal thallus will appear at first glance to have many more side branches than mentioned previously but can be seen on close inspection to have something of a zig-zag appearance representing the successive axes). The comb-like pattern of the branching is particularly evident in terminal branches of the thallus. In section, the axes have a disorganised cortex surrounding the central axial cells. Plocamiaceae have the standard triphasic red algal life cycle with gametophytes and sporophytes similar in outward appearance. Cystocarps appear to be more or less globular and borne along axial margins. Tetrasporangia are borne on the underside of modified branchlets called stichidia in a manner reminiscent of the sporangia of ferns (Gabrielson & Scagel 1989).

Close-up on terminal brachlets of Plocamium coccineum, copyright Fernan Federici. Some tetrasporangia-bearing stichidia are visible in the lower part of the image.


Only a few species have been described to date of the other genus of Plocamiaceae, Plocamiocolax. Though its reproductive anatomy demonstrates its relationship to Plocamium, Plocamiocolax is very different in its superficial appearance. It is a parasite, specifically a parasite of its sister genus. As such, they exhibit greatly reduced thalli and coloration. They grow on the host Plocamium as wartlike cushions, up to about five millimetres in diameter. As the cushion grows, it produces short, flattened projections that may be simple or forked. Tetrasporophytes may bear tetrasporangia on greatly reduced stichidia or on partially endophytic, verrucose patches.

Plocamiocolax pulvinata growing on Plocamium, copyright Michael Hawkes.


Parasitic forms that are closely related to the species they infect are referred to as 'adelphoparasites', meaning 'sister-parasites'. Adelphoparasitism is remarkably common among red algae: of over sixty known genera of parasitic red algae, about 90% are adelphoparasites (Salomaki & Lane 2014). One of the very first posts I ever wrote on this site was about red algal adelphoparasites, way back in...(gosh, really?...doesn't time fly when you're marching unceasingly towards oblivion...) It is possible that the regularity of this phenomenon is related to a distinctive feature of red algal development: the ability to open connections between adjacent cells allowing the passage of cytoplasm and organelles. Though the primary function of this process is presumably to facilitate the transfer of cellular products between cells of a single individual, it is not difficult to imagine a scenario where one individual hijacks another. The more closely related the adjacent cells, the greater the chance of an illicit connection succeeding. And succeeding multiple times. Though treated as a distinct genus, 'Plocamiocolax' lineages have apparently arisen within Plocamium multiple times (Goff et al. 1996). In some cases, a Plocamiocolax species proves to be the direct derivative of the Plocamium species they are found infesting. In others, a Plocamiocolax has arisen on one host species but later made the switch to another. Children are supposed to become independent and find their own way in the world, but sometimes the blighters just won't leave.

REFERENCES

Gabrielson, P. W., & R. F. Scagel. 1989. The marine algae of British Columbia, northern Washington, and southeast Alaska: division Rhodophyta (red algae), class Rhodophyceae, order Gigartinales, families Caulacanthaceae and Plocamiaceae. Canadian Journal of Botany 67: 1221–1234.

Goff, L. J., D. A. Moon, P. Nyvall, B. Stache, K. Mangin & G. Zuccarello. 1996. The evolution of parasitism in the red algae: molecular comparisons of adelphoparasites and their hosts. Journal of Phycology 32: 297–312.

Salomaki, E. D., & C. E. Lane. 2014. Are all red algal parasites cut from the same cloth? Acta Societatis Botanicorum Poloniae 83 (4): 369–375.

Saunders, G. W., & G. T. Kraft. 1994. Small-subunit rRNA gene sequences from representatives of selected families of the Gigartinales and Rhodymeniales (Rhodophyta). 1. Evidence for the Plocamiales ord.nov. Canadian Journal of Botany 72: 1250–1263.

Air-breathing Limpets

For many people, the most familiar members of the gastropods are the terrestrial snails. Gastropods started their evolution as marine animals, breathing through gills, but members of one lineage would instead evolve their own version of a lung, a large hollow in the mantle cavity opening through a hole alongside the head called the pneumostome. Possession of this lung cavity would enable slugs and snails to thrive in the terrestrial environment but the structure had originally evolved in a marine context, and even today one may find marine lung-bearers occupying habitats along the coast. One such group is the siphon limpets or 'false limpets'* of the Siphonarioidea.

*You know, normally I don't overly concern myself with vernacular names. They are not regulated and not obliged to follow reason. But even so, the name 'false limpet' makes me grit my teeth. The name is presumably inspired by the fact that siphonariids are not direct relatives of the 'true' limpets of the Patellogastropoda. But the limpet morphotype, where the typical spiral gastropod shell is reduced to a simple cap, has evolved on multiple occasions. As well as the siphonariids and patellogastropods, there are the keyhole limpets of the Fissurellidae, the freshwater limpets of the Ancylini, and many others, all consistently referred to as 'limpets'. The name refers to a morphology, not to a clade, and by that measure the siphonariids are no more 'false' than any other limpets.

Flat siphon limpets Siphonaria atra, copyright Ria Tan.


Living siphonarioids are placed within a single family, the Siphonariidae, whose members with their cap-shaped, often radially ribbed shells are found in littoral environments in temperate and tropical regions of the world. A second family, the Acroreiidae, is recognised from the Cretaceous and early Tertiary; the inclusion of these smooth, thin shells in the Siphonarioidea is somewhat tentative (classification of limpets in the fossil record is always a challenge because their simple shell form renders them light on distinguishing characters). Siphonariids are readily distinguished from other living limpets by the presence of a groove on the underside of the right side of the shell marking the position of the pneumostome. In dorsal view, this groove is often indicated by an asymmetry in the outline of the shell with one side produced. The pneumostome is also associated with a broad gap in the ring of muscle holding the shell in place; the ring is more complete in other limpets. Seemingly as a result of this lower extent of muscle, siphonariids cling to their home rocks with less tenacity than other limpets and are mostly restricted to more sheltered locations (Simone & Seabra 2017). On the other hand, they do have a more flexible foot than their competitors, allowing them to potentially move more quickly. Like other limpets, siphonariids are grazers, scraping microalgae as they crawl about. Siphonariids have a weaker radula than patellogastropods and so scrape somewhat less forcefully; when members of the two clades occupy the same habitats, patellogastropods are generally the more abundant. The majority of siphonariids (where known) have planktonic larvae but some species are known to be direct developers.

Siphonaria lessonii, copyright Mikelzubi.


Obviously, the marine but lung-possessing siphonariids are potentially of great interest in understanding how the gastropod lung evolved. Many earlier researchers thought that the siphonariids may have evolved from terrestrial ancestors who had returned to the seashore but this is no longer thought likely to be the case. In most lunged gastropods, gas exchange is effected in the mantle cavity via dense blood vessels in the cavity wall but in siphonariids a gill structure is present within the lung (this lung-gill combination makes the siphonariids particularly well suited for moving freely both above and below the water surface). The gill of siphonariids is quite similar to that of the sacoglossans, a group of herbivorous sea-slugs. Though it was long presumed that the lung-bearing gastropods belonged to a single clade, more recent molecular phylogenies have confused the issue (Kocot et al. 2013). The sacoglossans are likely to be close to the ancestry of lunged gastropods as a whole, but it is possible that siphonariids are more closely related to the sacoglossans than the other lung-bearers. It remains an open question whether the siphonariid combination of lung and gill represents an intermediate stage towards the vascular lung of the terrestrial forms, or whether siphonariids and other lung-bearers each evolved their pneumostome from close but distinct ancestors.

REFERENCES

Bouchet, P., J.-P. Rocroi, B. Hausdorf, A. Kaim, Y. Kano, A. Nützel, P. Parkhaev, M. Schrödl & E. E. Strong. 2017. Revised classification, nomenclator and typification of gastropod and monoplacophoran families. Malacologia 61 (1–2): 1–526.

Simone, L. R. L., & M. I. G. L. Seabra. 2017. Shell and body structure of the plesiomorphic pulmonate marine limpet Siphonaria pectinata (Linnaeus, 1758) from Portugal (Gastropoda: Heterobranchia: Siphonariidae). Folia Malacologia 25 (3): 147–164.

The Colletinae: Going to Ground

In a recent post, I considered one of the families of short-tongued bees, the Halictidae. In this post, I'll turn my attention to members of one of the other short-tongued bee families, the Colletidae. Specifically, I'm looking at members of the subfamily Colletinae.

Mating ball of male ivy bees Colletes hederae, copyright Charles J. Sharp.


Members of the Colletidae differ from other bee families in that their glossa, the 'tongue' at the end of the proboscis, is apically bilobed or bifurcate. They are also distinctive in lining their nests with a plasticky, cellophane-like material. It has been thought that this material was made from dry saliva but the bulk of it is now known to come from a large gland in the abdomen that opens near the base of the sting (Almeida 2008). A nesting female will swallow droplets of the glandular secretion from her partially protruded sting then regurgitate it as she licks the wall of the nest cell. This waterproof lining both protects the cell from outside elements while preventing the loss of moisture from within. Many colletids, including colletines, leave the cell food provisions in a semi-liquid state; other bees whose nests are less watertight will dry and compact the provisions, presumably because the bulk of them would otherwise be lost before the larva hatched. In colletines, the egg is attached to the cell lining when laid, suspended above the provisions for the hatching larva to swandive into upon emergence. All colletids are solitary nesters with species nesting either in burrows in the ground or in hollows in vegetation; the majority of colletines are ground nesters*.

*One species, Colletes daviesianus, has apparently taken in Germany to boring its nests in the sandstone and mortar used in building construction.

Female Colletes daviesianus, copyright Donald Hobern.


In his 2007 edition of The Bees of the World, Charles Michener recognised five subfamilies within the Colletidae. The Colletinae were distinguished from three of these subfamilies by their retention of a covering of dense hair over the body (from the last subfamily, the Diphaglossinae, they differ in features of the glossa and wing venation). The hind leg of the female bears a well-developed scopa (dense arrangement of hairs for the carrying of pollen) on the femur and tibia with a corbicula (bare patch within the scopa where a ball of compacted pollen may be carried) on the underside of the femur. Hairiness is an ancestral characteristic for bees and phylogenetic studies have established that the Colletinae as recognised by Michener is a paraphyletic grouping (e.g. Almeida & Danforth 2009). As a result, it has been further subdivided with the name 'Colletinae' now restricted to what Michener had recognised as the tribe Colletini. As such, the Colletinae now includes just two genera of moderate-sized bees (seven to sixteen millimetres in length). The larger of these, Colletes, is found in temperate and tropical regions around the world except for the Indo-Australian region where it is notably absent. The other genus, Maurecolletes, is restricted to South America. One of the most distinctive features of Colletinae in the strict sense compared to other ex-colletines is the lack of the basitibial and pygidial plates, flattened and hardened plates possessed by other hairy colletids at the base of the hind tibia and at the end of the abdomen.

The absence of these plates is intriguing in light of the ground-nesting habits that seem to be the norm for Colletes (the nesting habits of Maurecolletes seem to be unknown). In other ground-nesting bees, the basitibial and pygidial plates are used to press the soil of the nest walls and opening into place. One would think this would mitigate against their loss. An explanation may be provided by the fact that some South American Colletes nest in the hollows of dead, pithy plant stems instead of in the ground, a characteristic shared with members of the less hairy colletid subfamilies belonging to the sister group of the colletines (Almeida & Danforth 2009). Ground-nesting Colletes species also bear noteworthy resemblances to stem-nesting colletids. Nest cells are closed with a layer of the cellophane-like wall membrane rather than the earthen plugs used by other ground-nesting bees. In many species, cells are lined up in a burrow divided by transverse partitions rather than placed in their own individual side branches. The possibility has been suggested that stem-nesting arose within the common ancestors of modern colletines and less hairy colletids. Ground-nesting in Colletes would then represent a secondary reversion by these species to the previous habit. When they did so, they retained the adaptations and habits that had originally been associated with their time in the twigs.

REFERENCES

Almeida, E. A. B. 2008. Colletidae nesting biology (Hymenoptera: Apoidea). Apidologie 39: 16–29.

Almeida, E. A. B., & B. N. Danforth. 2009. Phylogeny of colletid bees (Hymenoptera: Colletidae) inferred from four nuclear genes. Molecular Phylogenetics and Evolution 50: 290–309.

Michener, C. D. 2007. The Bees of the World 2nd ed. John Hopkins University Press: Baltimore.

Colpochila: The Chafing of a Mega-genus

Just a few weeks ago, I discussed the melolonthines, a hyperdiverse group of beetles including the chafers that have historically presented something of a taxonomic challenge. In the comments on that post, Adam Yates brought up one aspect of the difficulties presented by this group that I hadn't gotten around to discussing. This is the presence among melolonthines of a number of what may be called 'mega-genera', large genera containing literally hundreds of species that defy attempts to break them down into more manageable units. So on that note, it's only appropriate that I move on to an example of one of these mega-genera, Colpochila.

Colpochila obesa, from Insects of Tasmania.


Colpochila is an Australian genus of melolonthines belonging to a group currently recognised as the tribe Liparetrini (Britton 1986) though readers of the earlier post may recall that relationships between Australian melolonthines and taxa elsewhere in the world remains something of an open question. Liparetrins are, on the whole, a fairly generalised group: characters of the group include a lack of metallic coloration, a labrum which sits underneath and is not fused to the clypeus, simple claws, and relatively broad hind tibiae that end in a pair of widely separated spurs that are placed one above and one below so that the tarsus when moved from side to side can move between the spurs. The two largest genera in the tribe, by a significant margin, are Colpochila and Liparetrus. Somewhere in the region of 130 species are currently recognised in Colpochila whereas Liparetrus is even more diverse. However, both genera were referred to by Britton (1986) as 'polythetic': that is, both represent assemblages of species that, while clearly connected to each other overall, are difficult to characterise from a diagnostic perspective. Species of the genus possess enough features in common that we can readily recognise them as related but it is difficult to drill down on any individual feature or set of features that is shared between all species without exception. Similarly, while I can say from experience that it is generally easy to tell at a glance whether a given species is a Colpochila or a Liparetrus, it is a lot harder to actually define what separates the two genera. The most obvious distinction is size: Colpochila species are relatively large chafers, over a centimetre in length, whereas Liparetrus are smaller. Other features that each separate most Colpochila species from most (though not all) Liparetrus are circular eyes (most Liparetrus have eyes with flattened edges in back so the eye is closer to semi-circular), antennae with more segments in the terminal club, longer elytra that leave less of the end of the abdomen exposed, and hind coxae without the translucent margins found in many Liparetrus.

The lifestyles of Colpochila species are still not very well known. As with other melolonthines, most of the life is spent underground with mature adults only emerging very briefly to breed. The active adults fly at night and may be attracted to lights; it seems unclear whether they feed at maturity. This genus is mostly found in drier habitats such as open woodland, grasslands or semi-desert (mind you, this is Australia we're talking about; drier habitats are 90% of what's going). Of the known species, over half are found in Western Australia.

A second Colpochila species, from Friends of Queens Park Bushland.


So why are Colpochila and other melolonthine mega-genera so diverse? It should be noted that straight geographical and/or ecological divergence does not appear to be the reason: not only is it possible to find multiple species of a single genus in one location but one may even collect very similar species together. It might be that the diversity of the mega-genera is artefactual, a reflection of the failure of taxonomists to properly identify relationships: any study that wanted to explain their diversity would have to study their phylogenetic relationships with related smaller genera to confirm their evolutionary coherence and/or age of divergence. However, if the current generic classification of melolonthines reflects a real evolutionary pattern, a potential explanation was proposed by Britton (1986). Adult melolonthines do not emerge immediately upon maturing but remain dormant underground awaiting a suitable environmental signal such as rainfall. However, rainfall in the arid zone at any one time is often uneven. Dormant beetles at one spot may feel the urge to emerge while others nearby may be left to wait for the next shower. The first wave will have died off before the second wave emerges, and their offspring will not yet be mature. As a result, sub-populations in a single region may become temporally staggered allowing the possibility of divergence via genetic drift. Eventually, their emergence times may drift back into sync but by then they may no longer be able to breed successfully. Could this be the reason why so many species may be found in a single location or may other factors be more significant?

REFERENCE

Britton, E. B. 1986. A revision of the Australian chafers (Coleoptera: Scarabaeidae: Melolonthinae) vol. 4. Tribe Liparetrini: genus Colpochila. Australian Journal of Zoology, Supplementary Series 118: 1–135.

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.