Field of Science

Silicon Rockets

In a previous post, I spoke of the radiolarians, marine protists renowned for their intricate skeletons, and the major radiolarian group known as the Spumellaria. Standing in contrast to the spumellarians is another major group, the Nassellaria. Like spumellarians, nassellarians have a skeleton of silica but whereas the basic shape of spumellarian skeleton is a sphere, that of nassellarians is a cone, bell or some similar shape, arranged along a longitudinal axis. The origination point of the skeleton is at or near the top of the cone and is known as the cephalis (from the Greek for 'head'). There may be an apical spine rising above the cephalis. Below it, the skeleton is commonly divided into recognisable sections referred to as the thorax, abdomen and post-abdominal segments (if present). The nucleus of the cell is more or less associated with the cephalis, contained within it at least during the juvenile stage of development though it may shift below the cephalis as the cell matures (Suzuki et al. 2009).

Skeleton of a Eucyrtidium sp., copyright Picturepest.


As is commonly the case with unicellular organisms, radiolarian taxonomy has been influenced by disagreements about which features should be regarded as more significant. Some would arrange taxa based on the overal formation of the skeleton. Others would focus on the development of the initial embryonic spicule around which the cephalis develops. A recent phylogenetic analysis of living nassellarians by Sandin et al. (2019), based on both morphological and molecular data, found that overall skeleton morphology was a much better indication of relationships than the internal structure. One well supported subgroup of the Nassellaria is the superfamily Eucyrtidioidea.

Eucyrtidioids have a fossil record going back to the Triassic (Afanasieva et al. 2005). The cephalis is spherical and clearly distinguished from the following segments by a constricted basal aperture. The test is usually multi-segmented; members of the subfamily Theocotylinae may have just two segments but other members of Eucyrtidiidae have up to ten segments. Fossil families assigned to Eucyrtidioidea by Afanasieva et al. (2005) may have up to twenty (but as Afanasieva et al.'s concept of Eucyrtidioidea was not found to be monophyletic by Sandin et al., the affinities of these fossil families perhaps warrant re-investigation). Segments are commonly divided by distinct inner rings. The skeleton lacks feet, the term used for protruding spines around the basal aperture of the skeleton found in many other nassellarians.

The phylogeny of nassellarians indicated by Sandin et al. (2019) places the Eucyrtidiidae as the sister taxon to other living nassellarians. Other living families included in the Eucyrtidioidea by Afanasieva et al. (2005) were placed in more nested positions. The implication is that the multi-segmented condition may be ancestral for crown Nassellaria. Segments are added progressively during the life of the radiolarian, leading the organism to look quite different at different ages. Indeed, this metamorphosis is pronounced enough that one of the earliest influential researchers on radiolarians, Ernst Haeckel (he of Kunstformen der Natur fame), made the mistake of classifying different ages as different species, genera and even families. Our understanding may be better than in Haeckel's time but there may still be a lot to learn about these intricate organisms.

REFERENCES

Afanasieva, M. S., E. O. Amon, Y. V. Agarkov & D. S. Boltovskoy. 2005. Radiolarians in the geological record. Paleontological Journal 39 (Suppl. 3): S135–S392.

Sandin, M. M., L. Pillet, T. Biard, C. Poirier, E. Bigeard, S. Romac, N. Suzuki & F. Not. 2019. Time calibrated morpho-molecular classification of Nassellaria (Radiolaria). Protist 170: 187–208.

Suzuki, N., K. Ogane, Y. Aita, M. Kato, S. Sakai, T. Kurihara, A. Matsuoka, S. Ohtsuka, A. Go, K. Nakaguchi, S. Yamaguchi, T. Takahashi & A. Tuji. 2009. Distribution patterns of the radiolarian nuclei and symbionts using DAPI-fluorescence. Bulletin of the National Museum of Nature and Science, Series B 35 (4): 169–182.

Tricolia: Fluorescent Seashells

Tricolia pullus, copyright Ar rouz.


Search among patches of seaweed along the shores of Africa, Australia or warmer parts of Eurasia and you may be able to find represents of the marine gastropod genus Tricolia. Tricolia are small shells, less than a centimetre in height, with shiny shells that may be smooth or spirally ribbed. Most species have a moderately high spire and an ovate shape but some are lower and more globose (Knight et al. 1960). The shell may or may not have an umbilicus, and there is a calcareous, externally convex operculum. Tricolia belongs to the Phasianellidae, commonly known as pheasant shells, presumably in reference to the bold, intricate colour patterns of many species. Species of Tricolia and the closely related genus Eulithidium, which replaces it in the Americas, have shell pigments containing porphyrin that fluoresce under ultraviolet light (Vafiadis & Burn 2020). Over forty species of Tricolia are currently recognised with the highest diversity in southern Africa (Nangammbi et al. 2016). However, the taxonomy of the genus has historically been confused due to polymorphic species being named multiple times; it is possible that at least some of the apparent African diversity is an artefact of the genus being largely unrevised in that region. An analysis of some of the southern African taxa by Nangammbi et al. (2016) found that some 'species' could not be distinguished genetically. They were, nevertheless, distinct geographically and the authors suggested that they may be variants of a single species responding to different environments.

Variants of Tricolia kochii, copyright Brian du Preez.


Like other members of the Vetigastropoda (the clade containing most of what used to be called the 'archaeogastropods'), Tricolia species have a simple life cycle without an actively feeding planktonic larva. The basic mode of reproduction is by broadcast spawning with separate males and females releasing gametes into the water column. After fertilisation, a brief non-feeding planktonic phase is nourished by yolk from the egg before the larva settles. The brevity of this phase is reflected by the resultant form of the protoconch which accounts for less than an entire whorl. In the Indo-West Pacific species T. variabilis, the male is smaller than the female and sits directly on her, waiting to fertilise her eggs as they are laid as gelatinous capsules rather than freely broadcasted. A temperate Australian species, T. rosea, takes things a step further as the female broods embryos (up to nearly fifty at a time) within the cavity of the last shell whorl (Vafiadis & Burn 2020). How the eggs are actually fertilised remains unknown but all embryos within a brood are about the samesize and stage of development, indicating a single fertilisation event; perhaps males associate with females as in T. variabilis. After the young pheasant shells hatch or settle, they initially feed on diatoms and other microalgae until they eventually grow enough to move onto the seaweed fronds that will comprise their adult diet.

REFERENCES

Knight, J. B., L. R. Cox, A. M. Keen, R. L. Batten, E. L. Yochelson & R. Robertson. 1960. Gastropoda: systematic descriptions. In: R. C. Moore (ed.) 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 pp. I171–I351. Geological Society of America: Boulder (Colorado), and University of Kansas Press: Lawrence (Kansas).

Nangammbi, T. C., D. G. Herbert & P. R. Teske. 2016. Molecular insights into species recognition within southern Africa's endemic Tricolia radiation (Vetigastropoda: Phasianellidae). Journal of Molluscan Studies 82: 97–103.

Vafiadis, P., & R. Burn. 2020. Internal embryonic brooding and development in the southern Australian micro-snail Tricolia rosea (Angas, 1867) (Vetigastropoda: Phasianellidae: Tricoliinae). Molluscan Research 40 (1): 60–76.

Podagritus in Australia

The digger wasps of the tribe Crabronini are a widespread group distinguished by a boxy head shape and relatively stout mesosoma. They are not dissimilar to hairless bees and indeed are close relatives of that group. There is a wide diversity of crabronins around the world; among their representatives here in Australia are members of the genus Podagritus.

Podagritus cf. tricolor, from Insects of Australia.


Podagritus species are medium-sized, elongate crabronins, generally in the region of a centimetre in length (give or take a few millimetres). The gaster is pedunculate (that is, the first segment of the metasoma is drawn into an elongate peduncle). Other, finer features distinguishing them from related genera of crabronins include a palpal formula of 5-3 (referring to the number of segments in the maxillary and labial palps, respectively; 5-3 indicates that both palps are slightly reduced from the ancestral count for crabronins) and often the presence of a sharp subvertical ridge, the omaulus, near the front of the mesopleuron (the median plate on the side of the mesosoma). If the omaulus is not present as such, there is still a distinct curve where it would have been so the planes of the mesopleuron on either side are more or less perpendicular. Females have a well defined triangular, flat pygidial plate and males often have one as well (Bohart & Menke 1976).

Thirty species of Podagritus were recognised from Australia by Leclercq (1998). Other species of the genus are known from New Zealand and South America. Historically, the Australian species have been treated as a distinct subgenus Echuca from Podagritus elsewhere, based on features such as a well defined, flat prepectus and a weakly sculpted metapleuron. Leclercq, however, questioned the value of this distinction, noting the existence of a couple of Australian species sharing notable features in common with species found elsewhere, and suggested abandoning subgenera until the genus could be revised as a whole.

The natural history of Podagritus species in Australia remains poorly known. One species found in the east of the continent, P. leptospermi, has been found nesting in a sloping gravel bank (Bohart & Menke 1976). Burrows were near vertical and close to a foot deep, and contained two or three cells placed at the ends of lateral galleries (one cell per gallery). Entrances were surrounded by flat mounds of sand six to ten centimetres wide and were not closed while the female was out hunting. Cells were stocked with flies (Tachinidae and Therevidae, so presumably reasonably large) that were initially stored at the bottom of the burrow before being placed in the cell head inwards and belly up, in lots of four to six. The egg was attached to a fly between the head and thorax, so when the larva hatched it would find itself already in place on a welcoming bed of food.

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World. University of California Press: Berkeley.

Leclercq, J. 1998. Hyménoptères sphécides crabroniens d'Australie du genre Podagritus Spinola, 1851 (Hymenoptera, Sphecidae). Entomofauna 19 (18): 285–308.

Dealing with a Clingy Male

Diving beetles of the family Dytiscidae are a distinctive component of the freshwater environment in most regions of the world. They have an oval, streamlined body form and powerful hind legs, usually with fringes of stiff setae, that are ill-suited for movement on land but make them adept swimmers. They are also almost always capable fliers, allowing them to find their way to water bodies of any size from large lakes to small, temporary pools. Both adults and larvae are active hunters, preying on other aquatic arthropods or even small vertebrates. Most diving beetles are fairly dull in coloration but exceptions are found among members of the tribe Aciliini.

Sunburst diving beetle Thermonectus marmoratus, from Insectarium de Montréal, René Limoges.


Members of the Aciliini are moderately sized diving beetles, generally between one or two centimetres in length. Dorsally they have a yellow to red base coloration with contrasting dark markings. The hind legs are robust with the hind tibia short and broad. Males have the base of the tarsus of the front legs broadened into a round palette with setae on the underside modified into sucking discs, used to hang onto the females when mating; this discs may be present on the tarsus of the mid pair of legs as well. They are strong swimmers, often venturing into the open waters of lakes and pools, and contrast with other diving beetles in that they may be found in pools lacking submerged vegetation (Roughley & Larson 2001; Bergsten & Miller 2006). Larvae have a distinctive arched body shape with a small head (Bukontaite et al. 2014), kind of shrimp-like, and also tend to be more pelagic than the larvae of other diving beetles. Females have gonocoxae (the appendages at the end of the abdomen that function as the ovipositor) that are relatively long with a broadened, spoon-like ending (Miller 2001); these are used to insert eggs into damp moss or under loose bark of vegetation lying just above the waterline. There is usually just one generation per year and adults in cold regions overwinter in larger water bodies that remain unfrozen.

Alternate morphs of female Graphoderus zonatus with granular (left) and smooth elytra, from Holmgren et al. (2016).


Perhaps the most intriguing aspect of aciliin diving beetles regards their sexual dimorphism. As noted above, males have a set of suckers on the fore legs for hanging onto females when mating. However, females of some species have sculpted elytra rather than the smooth elytra of males, such as a granular surface in Graphoderus species or long, setose sulci in female Acilius. The uneven surface produced by these features presumably functions to reduce the efficacy of the males' suckers, allowing the females more control when selecting a mate. That such a conflict exists is supported by the observation that the more developed the males' sucker arrays in a population, the more likely the females are to have repellent sculpturing. Males of some diving beetle species have been observed grabbing at any female they encounter, followed by the female swimming rapidly and erratically in an attempt to shake the male off or knock him off against the substrate or objects in the water (Miller 2003). Where this becomes really interesting is that some species have dimorphic females with some females in the population having sculpted elytra whereas others are smooth. What could be the reason for such variation? The presence of both forms in the population suggests that neither has a complete advantage over the other. It may be that smooth-backed females trade reduced defenses for improved swimming ability. Alternatively, a defensive female may be able to ensure that only the strongest and most resilient males can mate with her, but runs the risk of not mating at all if she never encounters a male who can overcome her defenses. A less defensive female may be more vulnerable to any male she encounters but at least she's bound to be fertilised at some point.

REFERENCES

Bergsten, J., & K. B. Miller. 2006. Taxonomic revision of the Holarctic diving beetle genus Acilius Leach (Coleoptera: Dytiscidae). Systematic Entomology 31: 145–197.

Bukontaite, R., K. B. Miller & J. Bergsten. 2014. The utility of CAD in recovering Gondwanan vicariance events and the evolutionary history of Aciliini (Coleoptera: Dytiscidae). BMC Evolutionary Biology 14: 5.

Holmgren, S., R. Angus, F. Jia, Z. Chen & J. Bergsten. 2016. Resolving the taxonomic conundrum in Graphoderus of the east Palearctic with a key to all species (Coleoptera, Dytiscidae). ZooKeys 574: 113–142.

Miller, K. B. 2003. The phylogeny of diving beetles (Coleoptera: Dytiscidae) and the evolution of sexual conflict. Biological Journal of the Linnean Society 79: 359–388.

Roughley, R. E., & D. J. Larson. 2001. Dytiscidae Leach, 1815. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 156–186. CRC Press: Boca Raton.

Atropacarus

The little guy pictured above (photo copyright Scott Justis) is a representative of the box mite genus Atropacarus, members of which can be found in most parts of the world. Atropacarus is a genus of the Phthiracaroidea, a group of box mites characterised by the plates on the underside of body being relatively wide, in contrast to the narrow ventral plates of its sister group, the Euphthiracaroidea (members of which have featured on this site before: here and here). The difference in configuration of these plates reflects a difference in the way that the body is contracted to allow legs and prosoma to be withdrawn beneath the protective cover of the notogaster. In euphthiracaroids, the sides of the notogaster are contracted inwards; in phthiracaroids, the ventral plates of the body are lifted upwards (Schmelzle et al. 2015).

The classification of phthiracaroids is subject to conflict with two main systems in the recent literature. In one, championed by the Polish acarologist Wojciech Niedbała, the phthiracaroids are divided between two families with Atropacarus in the Steganacaridae. Species of Atropacarus have the surface of the notogaster extensively covered with dimples. The dorsal seta on the tibia of the fourth leg is short and closely associated with a solenidion (a type of specialised sensory hair). The setae of the genital plate are arranged in a more or less straight row along the inner margin of the plate with the fifth and sixth setae further apart than the fourth and fifth (Niedbała 1986). Niedbała divides Atropacarus between two subgenera. In Atropacarus sensu stricto, there are sixteen or more pairs of setae on the notogaster and the second adanal seta is moved inwards on the ano-adanal plate to form a more or less straight line with the anal setae. In Hoplophorella, there are fifteen pairs of setae on the notogaster and the second adanal seta is distinctly laterally placed relative to the anal setae.

The super-hairy Atropacarus niedbalai, from Liu & Zhang (2013). Scale bar = 100 µm.


In the competing system, used for instance by Subías (2019), Atropacarus and Hoplophorella are treated as distinct genera and each is in turn divided into subgenera by the number of setae on the ano-adanal plate. To a certain extent, of course, the question of whether to treat Atropacarus and Hoplophorella as genera or subgenera is arbitrary. Nevertheless, this arguably cosmetic distinction does relate to an underlying difference in theory. The classification of phthiracaroids used by Subías (2019) is a largely diagnostic one, inspired by a desire to facilitate specimen identifications. Niedbała's classification, in contrast, is intended to reflect phylogenetic relationships. Simple setal counts may be convenient when composing keys but one might question its overall phylogenetic significance. Neotrichy (increases in setal count by multiplication of the original setae) is not uncommon in phthiracaroids, particularly on the notogaster. Setal counts may vary between individuals of a single species and overall neotrichy reaches an extreme in the New Zealand species Atropacarus niedbalai. In this species, the basic count of fifteen or sixteen pairs of notogastral setae has been increased to 109 or 115 pairs, with further neotrichy on the prodorsum and ventral plates (Liu & Zhang 2013). Subías (2019) defends his choice of classification by arguing that Niedbała's key features are often difficult to discern. I sympathise with the difficulty but, as a wise man once said, species are under no obligation to evolve with regard to the convenience of taxonomists.

REFERENCES

Liu, D., & Z.-Q. Zhang. 2013. Atropacarus (Atropacarus) niedbalai sp. nov., an extreme case of neotrichy in oribatid mites (Acari: Oribatida: Phthiracaridae). International Journal of Acarology 39 (6): 507–512.

Niedbała, W. 1986. Système des Phthiracaroidea (Oribatida, Euptyctima). Acarologia 27 (1): 61–84.

Schmelzle, S., R. A. Norton & M. Heethoff. 2015. Mechanics of the ptychoid defense mechanism in Ptyctima (Acari, Oribatida): one problem, two solutions. Zoologischer Anzeiger 2015: 27–40.

Subías, L. S. 2019. Nuevas adiciones al listado mundial de ácaros oribátidos (Acari, Oribatida) (14a actualización). Revista Ibérica de Aracnología 34: 76–80.

The Font of the Placentals

The large-scale incorporation of molecular data into phylogenetics over the last few decades has caused a revolution in our understanding of life's evolution. Taxa whose interrelationships were previously regarded as intractable have been opened up to study, and many of our previous views on relationships have been forced to shift. Because conflict always makes for a good story, certain cases of the latter have become causes celebres, receiving extensive attention in both the technical and popular literature. One of these subjects of particular interest, not surprisingly, involves the relationships of the living orders of mammals.

Reconstruction of Arctostylops steini by Brian Regal, from Janis et al. (1998). The arctostylopids are a Palaeocene to Eocene group of mammals of uncertain affinities but probably belonging somewhere in the Boreoeutheria.


A lot of this attention has focused around the revelation of the Afrotheria, a grouping of animals (tenrecs, elephant shrews, hyraxes, aardvarks, elephants and manatees) with likely African origins that was completely unsuspected by studies based on morphological data only but which molecular studies have identified with ever-increasing levels of support. Recent molecular studies of placental phylogeny have agreed on three basal divisions within the placental mammals: the Afrotheria, the Xenarthra (armadillos, anteaters and sloths, a grouping that was recognised even before the advent of molecular data), and the remaining placentals in the largest of the three, the Boreoeutheria.

To the best of my knowledge, the Boreoeutheria is a clade that has also so far been supported by molecular data only with no morphological features yet recognised as defining the group. Nevertheless, its support can be considered as well established. The name Boreoeutheria refers to the clade's likely northern origins in contrast to the more southern distribution of the other two. Within the Boreoeutheria, molecular studies indicate a basal divide between the Euarchontaglires on one side and the Laurasiatheria on the other. The Euarchontaglires include the primates and rodents (as well as a handful of smaller orders). The Laurasiatheria include the Eulipotyphla, a group of insectivorous mammals including shrews, moles and hedgehogs, as sister to a clade containing bats, carnivorans, perissodactyls and artiodactyls.

Molecular phylogeny of mammals, from Springer et al. (2004) (note that not all branches shown in this tree are supported by all studies).


This all has interesting ramifications for the early evolution of placentals. There is an extensive fossil record of mammals from the Palaeocene, the epoch of time immediately following the end of the Cretaceous. However, most of these mammals do not belong to the orders alive today and their exact relationships to living mammals remain open to debate. The molecule-induced shake-up of pacental relationships just increased this uncertainty: for instance, the interpretation of a given group of fossil mammals as close to the common ancestry of perissodactyls and elephants rather goes out the window when perissodactyls and elephants are no longer thought to be closely related. And detailed studies that may resolve these issues remain few and far between. One of the most notable analyses in recent years has been that by Halliday et al. (2017) which covered most of the well-preserved placentals and their close relatives from the Cretaceous and Palaeocene periods. However, it is difficult to say just what to make of their results. The unconstrained analysis of their data presents results that remain deeply inconsistent with the molecular tree. Conversely, constraining the analysis to more closely match the molecular data provides results that are intriguing but difficult to accept at face value; I suspect they may be artefacts of the algorithm forcing taxa into the least unacceptable position for inadequate data. Suggesting that pangolins are the last specialised survivors of a broad clade of condylarths, pantodonts, notoungulates and creodonts is... I suppose not a priori impossible, but definitely a big call. A later analysis based on an expanded version of the same data set by Halliday et al. (2019) irons out some of the kinks but still fails to resolve the base of the Boreoeutheria beyond a massive polytomy of 25 branches (an icosipentatomy?). The Euarchontaglires are recovered as a clade but not the Laurasiatheria or any of its molecular subgroups above the ordinal level. And while some of the newer analysis' placements may seem like an improvement (notoungulates are placed as the sister to litopterns instead of hanging out with pangolins), others may still raise an eyebrow (mesonychids are associated with carnivorans but viverravids and miacids are not).

As always, the best answer to this conundrum is likely to involve more research. While researching this post, I did come across comments from people suggesting issues with the Halliday et al. data. Frankly, for a data set of this size (involving 248 taxa and 748 characters in the 2019 paper), it would be incredible were it otherwise. I know from my own experience that as you add more characters and taxa to a phylogenetic analyses, the challenge of keeping everything in line rises exponentially, and the data sets I've dealt with have been nowhere near the size of this one. Nevertheless, it's a start. And we can but hope that even those who find fault with it ultimately take it as inspiration to themselves do better.

REFERENCES

Halliday, T. J. D., M. dos Reis, A. U. Tamuri, H. Ferguson-Gow, Z. Yang & A. Goswami. 2019. Rapid morphological evolution in placental mammals post-dates the origin of the crown group. Proceedings of the Royal Society of London Series B—Biological Sciences 286: 20182418.

Halliday, T. J. D., P. Upchurch & A. Goswami. 2017. Resolving the relationships of Paleocene placental mammals. Biological Reviews 92 (1): 521–550.

Bucklandiella lusitanica

The diversity of mosses is much higher than many people realise. Whereas some moss species have wide ranges that may cross between continents and hemispheres, others are unique to very specific regions and habitats. Among examples of the latter is the European species Bucklandiella lusitanica.

Illustrations of Bucklandiella lusitanica, from Ochyra & Sérgio (1992). Top left: habit; top right: section of stem of hair-leafed form when dry; lower left: section of stem of hairless form and sporophyte when wet.


Bucklandiella lusitanica was only described as a new species (under the name Racomitrium lusitanicum) in 1992 (Ochyra & Sérgio 1992), having gone unnoticed previously despite being a relatively distinctive species. Recent collections of the species have been identified from a single region, the Serra do Gerês mountain rainge and Parque Natural da Peneda-Gerês national park in the northwest of Portugal, at altitudes between 650 and 1000 metres. A single collection from the Serra do Estrela further south in the country was made in the mid-1800s though it went unidentified at the time. Its rarity is such that is has officially been listed as Endangered by the IUCN. Bucklandiella lusitanica is a rheophyte, which is to say that it grows in association with running water. It grows on acidic granite rocks that are periodically or permanently submerged, such as alongside streams and waterfalls. It is particularly abundant on steep rock faces, growing in association with closely related moss species.

Appearance-wise, Bucklandiella lusitanica is a medium-sized moss with irregularly branched stems growing 1.5 to 3.5 centimetres in length. Leaves are rigid, held tight to stem, and two or three millimetres long.One of the species' most distinctive features is a broad, fleshy margin to each leaf that is generally two or three cells thick whereas the lamina of the leaf is mostly only a single cell thick. The alar cells at the base of the sides of the leaf often form inflated, strongly coloured lobes. The leaves commonly end in a fine, colourless hair-point. The structure of the leaves is similar to that of Bucklandiella lamprocarpa, another aquatic moss species, but that species lacks the hair-points. The two species also differ in the form of their spores, those of B. lamprocarpa being larger and more ornate than those of B. lusitanica, and B. lamprocarpa has fatter and often shinier capsules than B. lusitanica.

I mentioned previously that Bucklandiella lusitanica was originally described as a member of the genus Racomitrium. The moss genus Racomitrium was long recognised by a distinctive array of features including leaf lamina cells with distinctly sinuous longitudinal cell walls, a calyptra (the cap of the developing capsule) that is basally frayed into several lobes, and teeth of the peristome (the teeth around the aperture of a mature capsule) that are split into two or more segments (Sawicki et al. 2015). Racomitrium in this sense was a diverse genus with over two hundred species having been named at one time or another, and somewhere between sixty and eighty species recognised as valid in recent years, As a result, Ochyra et al. (2003) proposed the division of Racomitrium in the broad sense between four separate genera. Bucklandiella, the largest of these segregate genera (with about fifty currently known species), was recognised for species with a smooth leaf surface (lacking papillae on the lamina) and relatively short, shallowly divided teeth in the peristome. The division of Racomitrium has not been universally accepted. Larrain et al. (2013) questioned the monophyly and diagnosability of Ochyra et al.'s segregates but Sawicki et al. (2015) reiterated their support for the new system (and added a fifh new segregate genus to boot). It is generally accepted that Racomitrium in the broad sense represents a monophyletic unit, so the question of whether lusitanicum should be assigned to Racomitrium or Bucklandiella may largely be considered a question of just how closely circumscribed you feel a genus should be.

REFERENCES

Larraín, J., D. Quandt, M. Stech & J. Muñoz. 2013. Lumping or splitting? The case of Racomitrium (Bryophytina: Grimmiaceae). Taxon 62 (6): 1117–1132.

Ochyra, R., & C. Sérgio. 1992. Racomitrium lusitanicum (Musci, Grimmiaceae), a new species from Europe. Fragmenta Floristica et Geobotanica 37 (1): 261–271.

Ochyra, R., J. Żarnowiec & H. Bednarek-Ochyra. 2003. Census Catalogue of Polish Mosses. Institute of Botany, Polish Academy of Sciences: Cracow.

Sawicki, J., M. Szczecińska, H. Bednarek-Ochyra & R. Ochyra. 2015. Mitochondrial phylogenomics supports splitting the traditionally conceived genus Racomitrium (Bryophyta: Grimmiaceae). Nova Hedwigia 100 (3–4): 293–317.

The Glandulinid Position

In an earlier post, I described how the majority of modern multi-chambered foraminiferans can be divided between two lineages, the Tubothalamea and Globothalamea. The two groups generally differ in the shape of the first chamber following the proloculus (the central embryonic chamber of the test): in one, this chamber is tubular whereas in the other it is globular or crescent-shaped (guess which is which). But there is a third notable group of multi-chambered forams: the Nodosariata. In both tubothalameans and globothalameans, the chambers more or less coil around the proloculus to form a spiral. In the Nodosariata, the test is more or less linear with apical chamber apertures. The chambers may be successively stacked one after the other to form a uniserial test, or they may be arranged in a zig-zag or twirling arrangement to form biserial, triserial, etc. arrangments. In living Nodosariata, the wall of the test is made of a single layer of hyaline calcite though some earlier representatives (up to the end of the Jurassic) had differing wall make-ups (Rigaud et al. 2016). Among the numerous notable representatives of the Nodosariata in the modern fauna are representatives of the family Glandulinidae.

Series of Glandulina ovula, from Brady (1884).


Species have been assigned to the Glandulinidae going back to the Jurassic with the modern genus Glandulina recognisable in the Palaeocene (Loeblich & Tappan 1964). The test may be uniserial, biserial or polymorphine (more than two series); a common arrangement is for the test to start out biserial or polymorphine then become uniserial as the individual chambers become larger. In Glandulina, the microspheric generation starts biserial but the megalospheric form is uniserial throughout (Taylor et al. 1985). As the test grows, the internal walls between chambers may be resorbed. The terminal aperture of the test may be radial or slit-like. The most characteristic feature of the family is a tube running into the chamber from the inside of the aperture, referred to as the entosolenian tube. Some glandulinids have been described as lacking an entosolenian tube but such absences are likely artefacts of preservation: the delicate tube is easily dislodged during the fossilisation process (Taylor et al. 1985).

The overall relationships of the Nodosariata remain a question open to investigation. The classification of forams by Loeblich & Tappan (1964) included both multi-chambered and single-chambered (unilocular) forms within the Glandulinidae, with the unilocular forms placed in a subfamily Oolininae. Oolinines resemble glandulinids proper in a number of features including wall structure and the presence of an entosolenian tube. More recent authors, however, have rejected this relationship. Rigaud et al. (2016) entirely excluded unilocular forms from the Nodosariata as a whole, regarding it as improbable that single-chambered forms could have evolved from multi-chambered ancestors (as would seemingly be required by their relative appearances in the fossil record). Do the similarities between glandulinids and oolinines reflect a common ancestry, or are they the result of simple convergence? Unfortunately, with so few significant characters available to inform our understanding of foram higher relationships, the answer you prefer may come down to no more than your own personal feelings about which indicators are more reliable.

REFERENCES

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

Rigaud, S., D. Vachard, F. Schlagintweit & R. Martini. 2016. New lineage of Triassic aragonitic Foraminifera and reassessment of the class Nodosariata. Journal of Systematic Palaeontology 14 (11): 919–938.

Taylor, S. H., R. T. Patterson & H.-W. Choi. 1985. Occurrence and reliability of internal morphologic features in some Glandulinidae (Foraminiferida). Journal of Foraminiferal Research 15 (1): 18–23.

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.