Naviculi, Navicula

Diatoms are one of the most prominent groups of micro-algae in aquatic environments, perhaps more abundant than any other major group of aquatic organisms except bacteria. As such, they are a key component in many of the environmental processes that we ultimately depend on: food for aquatic animals, producers of oxygen, et cetera et cetera. To those who study them, they are also known for the intricate architecture of their silica walls. As well as being aesthetically pleasing, this architecture forms a key component of diatom classification. One of the most diverse groups of diatoms recognised has been the mega-genus Navicula.

Light microscope view of Navicula tripunctata, copyright Kristian Peters.

Historically, over one thousand species have been assigned to Navicula. Though more recent authors have restricted the name to a smaller, more tightly defined concept than before, it still contains some 200 or so species (Bruder & Medlin 2008). Species assigned to this genus are an elongate diamond or pill shape. Though the term 'navicula' can be translated from Latin as a small boat, and this is often assumed to be the name's origin, this is incorrect. Its original author, the French naturalist Jean-Baptiste Geneviève Marcellin Bory de Saint-Vincent, derived the name from the French term for a weaver's spindle (navette de tisserand; Cox 1999). A long fissure, the raphe, runs down the midline of each valve of the diatom wall; the diatom moves by extruding secretions through the raphe. In Navicula, the raphe is largely straight though it may be hooked at the ends of the valve. Perpendicular to or radiating from the raphe are striae formed of rows of openings (areolae); in Navicula, these areolae are more or less elongate with their long axes perpendicular to the line of the stria. In some species historically included in Navicula, the striae may be biseriate with two rows of areolae. Some authors have proposed recognising species with biseriate striae as a distinct genus Hippodonta. Cox (1999) disputed whether this distinction was enough to warrant a separate genus but Bruder & Medlin (2008) conducted a molecular phylogenetic analysis of naviculoid diatoms in which the one Hippodonta species included was placed as the sister taxon to Navicula sensu stricto. In distinguishing the genus Sellaphora from Navicula, Mann (1989) also identified a number of cytoplasmic features characteristic of Navicula sensu stricto, such as the possession of two distinct plastids per cell with rod-like pyrenoids.

SEM view of Navicula dobrinatemniskovae, from Van de Vijver et al. (2011). Scale bar = 1 µm.

Ecologically, the majority of species of Navicula sensu stricto (about 150 species) are found in freshwater environments (Bruder & Medlin 2008). In temperate and tropical regions, they are a diverse element of benthic diatom communities, but they are less predominant in coldwater habitats (Van de Vijver et al. 2011). They are most characteristic of meso- to eutrophic lakes and permanent waterways and Van de Vijver et al. (2011) therefore suggested that they might be less suited for the damp soils and temporary pools that dominate freshwater habitats in the frozen South. Nevertheless, these authors still managed to identify five previously unknown species from just this inhospitable region, giving some indication of what still remains to be discovered of this already diverse genus.

REFERENCES

Bruder, K., & L. K. Medlin. 2008. Morphological and molecular investigations of naviculoid diatoms. III. Hippodonta and Navicula s. s. Diatom Research 23 (2): 331–347.

Cox, E. J. 1999. Studies on the diatom genus Navicula Bory. VIII. Variation in valve morphology in relation to the generic diagnosis based on Navicula tripunctata (O. F. Müller) Bory. Diatom Research 14 (2): 207–237.

Mann, D. G. 1989. The diatom genus Sellaphora: separation from Navicula. British Phycological Journal 24 (1): 1–20.

Van de Vijver, B., R. Zidarova, M. Sterken, E. Verleyen, M. de Haan, W. Vyverman, F. Hinz & K. Sabbe. 2011. Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the sub-Antarctic and Antarctic with the description of five new species. Phycologia 50 (3): 281–297.

The Age of Olcostephaninae

Ammonites are among the iconic fossils of the Mesozoic. These shelled cephalopods dominated the oceans during their heyday and diversified into a wide array of taxa. Many of these have become significant for recognising particular periods in the earth's history; among these are members of the Olcostephaninae of the Early Cretaceous.

Olcostephanus astierianus, copyright Hectonichus.

The Olcostephaninae, as recognised by Wright et al. (1996), are known from the Valanginian and Hauterivian epochs of the Early Cretaceous, disappearing from the fossil record some time during the earlier part of the latter. The Valanginian ran from about 140 to 133 million years ago; the Hauterivian lasted for about three and a half million years after that. A brief reminder here: the Cretaceous lasted for a bloody long time, with more time separating the beginning and end of the Cretaceous than separates the end of the Cretaceous and today. One genus described from Pakistan, Provalanginites, has been supposed to come from the latest Jurassic but, as this is at least five million years earlier than any known olcostephanine anywhere else, its age is regarded as questionable. Olcostephanines can be very abundant in formations of the right age. A mass occurrence in the latest Valanginian of northwestern Europe has long been recognised as a geological marker, dubbed the 'Astierien Schichten' (Astieria being a synonym of Olcostephanus; Lukeneder 2004).

Saynoceras verrucosum, from here.

Olcostephanines are small to moderate-sized ammonites. Lukeneder (2004) refers to macroconches* of Olcostephanus guebhardi up to about ten centimetres in diameter. The olcostephanines pictured in Wright et al. (1996) seem to indicate an average size smaller than this and the group also includes a number of dwarf genera that look to only be a bit over one centimetre in diameter. The shell of olcostephanines is usually characterised by a pattern of transverse ribs coalescing in bundles to meet tubercles on the inner margin of the whorl. One dwarf genus, Saynoceras, has a stronger ornamentation of two rows of tubercles near the midline and outer margins of the whorls.

*A common pattern in ammonoids is the co-occurrence within a formation of distinct forms, termed 'macroconches' and 'microconches', that are broadly similar except in size and the configuration of the aperture (generally simple in macroconches but with protruding lappets in microconches). The most popular interpretation of this phenomenon is that the forms represent sexual dimorphism. Obviously which sex is which can't be known at this time though comparison with living cephalopods suggests that the macroconches may be female.

Valanginites nucleus, from here.

Olcostephanines are very similar in external appearance to the earlier subfamily Spiticeratinae (known from the very earliest part of the Cretaceous) and are likely to be descended from among that group. Though the Olcostephaninae themselves as currently recognised disappeared during the Hauterivian epoch, this may not have been the actual end of the olcostephanine lineage. The slightly later Holcodiscidae are very similar to the olcostephanines and some have questioned whether they even warrant separation. There is also a strong similarity between early members of the superfamily Desmoceratoidea and species of Olcostephanus (Wright et al. 1996). If this similarity also indicates ancestry, then the family line of the olcostephanines would continue right until the final extinction of the ammonites at the end of the Cretaceous.

REFERENCES

Lukeneder, A. 2004. The Olcostephanus level: an Upper Valanginian ammonoid mass-occurrence (Lower Cretaceous, Northern Calcareous Alps, Austria). Acta Geologica Polonica 54 (1): 23–33.

Wright, C. W., J. H. Calloman & M. K. Howarth. 1996. Treatise on Invertebrate Paleontology pt L. Mollusca 4, revised vol. 4. Cretaceous Ammonoidea. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

The Pireninae

The chalcidoid wasps are truly a remarkable array: tiny wonders coming in a bewildering variety of forms. For this post, I'm looking at the members of the chalcidoid subfamily Pireninae.

Macroglenes sp., copyright Charley Eiseman.

The Pireninae are currently recognised as one of the subfamilies of the Pteromalidae, a chalcidoid 'family' that is long overdue for reclassification as phylogenetic studies have agreed that it is extensively polyphyletic* (e.g. Heraty et al. 2013). The pirenines are very small wasps, about one to two millimetres in length. They've always struck me as having a fairly fly-like habitus: they lack the metallic coloration and strong sculpturing of many other pteromalids, often being uniformly black or yellow, and carry upright bristle-like setae on the head and mesosoma. Characteristic features of the Pireninae also include antennae inserted low on the face, reduced numbers of antennal segments (and hence often rather short antennae), a large clypeus that often protrudes ventrally, and a dorsally rounded mesosoma often with deeply impressed notauli (longitudinal grooves on the mesoscutum) (Bouček 1988). About ten genera are currently recognised in the subfamily. Perhaps the most remarkable is the genus Zebe, named by John La Salle in 2005 from a single female that he says, at the time, had stymied multiple hymenopterists as to what it might be for two decades. Zebe has legs with four-segmented tarsi, instead of the five-segmented tarsi of other pteromalids, and the female has a long horn extending forward from the mesoscutum and hanging over the head. As in other micro-wasps with comparable structures, this horn probably provides space for the retraction of an extraordinarily long ovipositor.

*But just in case anyone who stands to have some influence is reading, I will point out that the number of subfamilies that need to excised from the Pteromalidae could be kept to a minimum if the family is expanded to include the Ormyridae, Torymidae, Eucharitidae and Perilampidae. Bonus points that these are the families that are the hardest to distinguish from pteromalids to begin with.

Female Zebe cornutus, from Mitroiu (2011).

The life habits of most pirenines are very little known. Those whose hosts are known develop as parasites of Cecidomyiidae, gall midges, and may be found in association with the galls produced by those flies on various plants. Species of the genus Macrogelenes attack cecidomyiids associated with grasses, and some have been investigated as control agents for midges on commercial crops. So these tiny little wasps could prove themselves very valuable to humans.

REFERENCES

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

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

La Salle, J. 2005. Zebe cornutus gen. et sp. nov., a new Pireninae (Hymenoptera: Pteromalidae) with 4-segmented tarsi and a mesoscutal horn. Acta Societatis Zoologicae Bohemoslovenicae 69: 193–197.

Snakes and Lace

The holometabolous insects—that is, the clade containing most insects with a complex life cycle including differentiated larval and pupal stages—is one of the most extensive radiations of animals on this planet. Much of this diversity is assigned to four major orders: wasps, moths, beetles and flies. But there are also a number of smaller lineages making up the holometabolous insects. Among these are the lacewings and their relatives in the clade Neuropterida.

Female snakefly Puncha ratzeburgi, copyright Hectonichus.

Modern members of the Neuropterida are generally recognised as belonging to three orders—the lacewings and ant-lions in the Neuroptera, the snakeflies in the Raphidioptera, and the alderflies and dobsonflies in the Megaloptera—though go back a few decades and you may find texts referring to a single order Neuroptera. A number of authors have advocated for use of the name 'Planipennia' for the lacewing order to avoid confusion with the broader sense of Neuroptera but, while a case could certainly be made for this usage, it's just never really caught on. Most neuropteridans are fairly similar in overall appearance: long-bodied insects with well developed wings with numerous crossveins. Of the living holometabolous insects, they probably bear the greatest overall resemblance to the clade's ancestors and hence they are commonly thought of as 'relicts'. However, they do possess their own specialisations and are not primitive in every regard (for instance, the most primitive egg-laying apparatus among holometabolous insects belong to wasps). Species of Neuropterida are mostly predators as larvae. The larvae of the lacewing family Ithonidae may possibly feed on decaying plant matter though we don't know for certain (Grimaldi & Engel 2005). Adults are predators and/or pollen-feeders, or may not feed at all in some short-lived forms.

Male (above) and female dobsonflies Corydalus cornutus, copyright Didier Descouens.

The exact relationships between the neuropteridan orders have been debated over the years. Though most of their obvious similaities to each other represent shared ancestral features, there is a broad consensus that they do indeed form a clade. There has also been little, if any, question of the monophyly of the Raphidioptera and Neuroptera; the monophyly of Megaloptera has been more debated but seems more likely than not. Most recent studies have suggested that the Raphidioptera are the sister group to a clade of the other two orders (Engel et al. 2018). Raphidioptera are the least diverse of the generally recognised living orders of insects with about 250 known species. They are found in cooler regions of the Northern Hemisphere—in the temperate zone or at higher elevations in lower latitudes—and are completely absent from the Southern Hemisphere (Aspöck & Aspöck, 1991, refer to a failed attempt to introduce them to Australia and New Zealand but provide no details why such a thing was tried in the first place). They are characterised by a notably elongate prothorax (the first segment of the thorax) which explains the vernacular name of 'snakefly'. Larvae live under bark or in litter and moult into pupae with the onset of cold weather. The pupae of Raphidioptera and Megaloptera are primitive in aspect, with legs separate from the body wall, and are highly mobile. Engel et al. (2018) even refer to the pupae of Raphidioptera as 'active predators' but I've not been able to find corroborating details for that remarkable description.

The Megaloptera are often particularly large neuropteridans, reaching up to twenty centimetres in wingspan, and comprise a bit less than 400 species worldwide, mostly found in temperate regions. Larvae are aquatic, living under rocks and debris, and characterised by the presence of filamentous lateral gills on the abdomen. Adults are short-lived and feed little if at all. Male dobsonflies (of the subfamily Corydalinae) possess spectacularly large, curved mandibles of largely unknown purpose; certainly they do not seem to use them for biting.

Mantisfly Mantispa styriaca, a raptorial lacewing, copyright Gilles San Martin.

The largest of the three orders, by a considerable margin, is the Neuroptera with over 5700 known species. Needless to say, this level of species diversity is associated with a high diversity of appearances and lifestyles, too many to cover adequately here. The larvae of two families of Neuroptera, the Nevrorthidae and Sisyridae, are aquatic and there has been a long-running debate whether this aquatic habit is an ancestral feature of the order shared with the Megaloptera (Nevrorthidae larvae are generalist predators, Sisyridae are specialised feeders on freshwater sponges and bryozoans). However, recent phylogenetic studies (e.g. Vasilikopoulos et al. 2020) do not agree with earlier hypotheses that the Nevrorthidae represent the sister taxon of the remaining Neuroptera. Instead, Nevrorthidae and Sisyridae may form a clade with the Osmylidae, a family whose larvae are not aquatic but often inhabit damp stream banks. The aquatic Neuroptera probably entered the water independently of the alderflies. The current favourites for the sister clade of other neuropterans are the dustywings of the Coniopterygidae, a group of small neuropterans with reduced wing venation that have historically been difficult to place owing to their derived features.

An unidentified dustywing, Coniopterygidae, copyright Katja Schulz.

A fourth order has often been associated with the Neuropterida, the extinct Glosselytrodea. Glosselytrodeans are small insects known from the Late Permian to the Jurassic, characterised by wings bearing dense cross-veins of which the fore pair would have had a leathery appearance in life (not dissimilar in texture to the fore wings of grasshoppers and other Orthoptera). Other than the wings, the features of glosselytrodeans are poorly known: they seem to have been hypognathous (i.e. had the head directed downwards) with slender legs (Grimaldi & Engel 2005). Connections to Neuropterida are based on features of the wing venation but cannot be considered strongly supported. Other authors have regarded them as of uncertain position within the broader holometabolous clade, or even as more closely related to the Orthoptera than any Holometabola. Unless more complete remains should come to light, it seems likely that the question will remain open.

REFERENCES

Aspöck, H., & U. Aspöck. 1991. Raphidioptera (snake-flies, camelneck-flies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2^nd ed. vol. 1 pp. 521–524. Melbourne University Press.

Engel, M. S., S. L. Winterton & L. C. V. Breitkreuz. 2018. Phylogeny and evolution of Neuropterida: where have wings of lace taken us? Annual Review of Entomology 63: 531–551.

Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

Vasilikopoulos, A., B. Misof, K. Meusemann, D. Lieberz, T. Flouri, R. G. Beutel, O. Niehuis, T. Wappler, J. Rust, R. S. Peters, A. Donath, L. Podsiadlowski, C. Mayer, D. Bartel, A. Böhm, S. Liu, P. Kapli, C. Greve, J. E. Jepson, X. Liu, X. Zhou, H. Aspöck & U. Aspöck. 2020. An integrative phylogenomic approach to elucidate the evolutionary history and divergence times of Neuropterida (Insecta: Holometabola). BMC Evolutionary Biology 20: 64.

Mites of Southern Sediment

Water mites of the clade Hydrachnidiae are one of the few groups of arachnids that have not only adopted an aquatic lifestyle but have thrived and diversified there. Over fifty families are currently recognised within this clade, some of which can be found in almost every body of fresh water worldwide. Others, however, are notable for their restricted ranges. One of these latter examples is the Omartacaridae.

Ventral view of female Omartacarus elongatus, from Cook (1963).

Omartacaridae is a small family currently recognised as including only two genera, Omartacarus and Maharashtracarus. They have a somewhat elongated body with a soft integument, contrasting with the more globular form of many other water mites. They are also distinguished by the arrangement of the coxae (the basal segments of the legs on the underside of the body) which are clustered together with the medial edges of the anterior pairs much longer than those of the posterior pairs (Walter et al. 2009) so the third pair of coxae are triangular in shape. As far as is known, omartacarids are restricted to interstitial habitats or the hyporheic zone of sediment beneath and alongside stream beds. I am unaware of any direct observations of omartacarid behaviour but they are presumably predators like other water mites. Most of the (rather limited) attention that has been given to omartacarids has focused on discussions of their distribution. Species of Omartacarus are found in South and southern North America, as well as in Australia. Maharashtracarus species are known from India and Costa Rica. It has been presumed that this reflects an ancestral Gondwanan distribution, spreading into North America from South America as the continents joined.

The larval stage of omartacarids is, to date, unknown. Larvae of other water mites live as parasites of water-associated insects such as midges and omartacarid larvae are presumably also parasitic. But in what capacity? Do mature omartacarids emerge from their subterranean habitats at some particular time of year in search of a host for their eggs? Do they somehow manage to find a host while remaining safely sequestered underground? The secret remains to be uncovered.

REFERENCE

Walter, D. E., E. E. Lindquist, I. M. Smith, D. R. Cook & G. W. Krantz. 2009. Order Trombidiformes. In: Krantz, G. W., & D. E. Walter (eds) A Manual of Acarology 3^rd ed. pp. 233-420. Texas Tech University Press.

Arrow Poison and Arrow without Poison

Central and South America are home to a remarkable diversity of frogs, coming in nearly all the shapes and sizes a frog can possibly come in. Among this diversity, probably the most famous representatives are the arrow-poison frogs of the Dendrobatidae.

Two dendrobatid frogs of two different subfamilies: dyeing dart frog Dendrobates tinctorius (Dendrobatinae, left) and phantasmal poison frog Epipedobates tricolor (Colostethinae, right), copyright H. Krisp. Offhand, has someone been playing silly buggers with dendrobatid species names? Dendrobates auratus is green and black, not gold, and I'm sure I only see two colours on that E. tricolor.

The Dendrobatidae are themselves a diverse family, with somewhere in the area of two hundred currently recognised species. Many of these have only recently been recognised: nearly half of the currently known species have been named since 1985 (Grant et al. 2006). There are also ninety or so species in the closely related family Aromobatidae that were historically treated as dendrobatids and still may be in some sources. The Dendrobatidae are currently divided between three subfamilies: about half the species belong to the subfamily Dendrobatinae, a bit less than a quarter to the Colostethinae, and close to sixty species are placed in the genus Hyloxalus that forms its own subfamily (Grant et al. 2006).

Panama rocket frog Colostethus panamensis, copyright Brian Gratwicke.

Members of the Dendrobatidae are best known, of course, for their remarkable toxicity, associated with bright, striking warning colours. The name 'arrow-poison frog' reflects this trait as an arrow scraped across a frog's skin would pick up some of the frog's own lethality. The toxin, comprising various alkaloids, is not produced directly by the frog itself but is instead acquired through its arthropod diet. Most of the alkaloids sequestered by arrow-poison frogs come from ants (Darst et al. 2005) but other potential sources include beetles, millipedes and oribatid mites. However, not all dendrobatids are toxic and colourful. In fact, these features are largely characteristic of the Dendrobatinae only. Members of the Colostethinae and Hyloxalus are mostly cryptic in coloration and largely do not sequester alkaloids. The distinction is not an unshakeable rule: some non-dendrobatine dendrobatids are quite colourful in their own right and a handful of colostethines (members of the genus Epipedobates) are toxic, having seemingly evolved the ability to secrete alkaloids independently of the dendrobatines. Laboratory studies indicate that at least some non-toxic colostethines are able to consume alkaloid-bearing prey without ill effects, suggesting that alkaloid resistance is ancestral for the family as a whole.

Male Hyloxalus nexipus carrying tadpoles, copyright Santiago Ron.

More characteristic of dendrobatids as a whole is their breeding behaviour. As a rule, dendrobatids are more or less terrestrial, not habitually living in water, though many species are found alongside the margins of water bodies and may dive into the water to escape danger. Others will be found among leaf litter or be completely arboreal. Eggs are laid in damp terrestrial locations such as under leaves; males may deposit their sperm before or after the female deposits her eggs. Hatching tadpoles are then carried on the back of one of the parents to a suitable body of water such as a pool or stream. In members of the Dendrobatinae, tadpoles are deposited in phytotelmata, water-filled hollows in vegetation (such as in the cenre of bromeliads or holes in trees). Adelphobates castaneoticus, found in Pará in Brazil, has a habit of using the fallen husks of Brazil nuts. In some species, tadpoles are transferred one at a time; in others, groups of tadpoles will be carried en masse. In most genera, the male parent is the primary or sole transporter of tadpoles. Females of some species may also carry tadpoles; in others, a female finding an unattended cache of eggs will simply eat them. In the dendrobatine genus Oophaga, tadpole transport is the sole responsibility of the female. Following deposition, developing tadpoles of many species live on a diet of detritus. Others, particularly among the phytotelm-inhabiting species, are carnivorous, feeding on insects and other aquatic vertebrates, or even on their own siblings. In the aforementioned Oophaga, the transporting female will also lay a deposit of unfertilised eggs at the same time as she drops off the tadpoles. As well as providing food for the developing larvae, these eggs may also carry a shot of alkaloids to provide a head start in developing their defenses.

Strawberry poison-dart frogs Oophaga pumilio, two different colour morphs, copyright Pavel Kirillov.

Despite their often bright colours, many dendrobatids are poorly known due to cryptic habits and many species are only found in restricted ranges. As well as the usual threats to their survival from habitat destruction and the like, many dendrobatid species are threatened by collection for the pet trade. Their bright colours make dendrobatids popular specimens and captive individuals lose their toxicity if not provided with the prey from which alkaloids are derived. Unfortunately, about a quarter of dendrobatid species are currently recognised as endangered, many severely so. The highest diversity of endangered species is in the northern Andean region, in Venezuela, Colombia and Peru, which is also the centre of diversity for the family as a whole (Guillory et al. 2019). Urgent action may be required if we are to preserve these tiny, shiny, toxic beauties.

REFERENCES

Darst, C. R., P. A. Menéndez-Guerrero, L. A. Coloma & D. C. Cannatella. 2005. Evolution of dietary specialization and chemical defense in poison frogs (Dendrobatidae): a comparative analysis. American Naturalist 165 (1): 56–69.

Grant, T., D. R. Frost, J. P. Caldwell, R. Gagliardo, C. F. B. Haddad, P. J. R. Kok, D. B. Means, B. P. Noonan, W. E. Schargel & W. C. Wheeler. 2006. Phylogenetic systematics of dart-poison frogs and their relatives (Amphibia: Athesphatanura: Dendrobatidae). Bulletin of the American Museum of Natural History 299: 1-262.

Guillory, W. X., M. R. Muell, K. Summers & J. L. Brown. 2019. Phylogenomic reconstruction of the Neotropical poison frogs (Dendrobatidae) and their conservation. Diversity 11: 126.

The Spread of Carrots

Carrots are one of the staple vegetables in this part of the world as well as in a great many others. Indeed, Wikipedia informs us that about forty million tonnes of carrots and turnips were produced worldwide in 2018, and I would have to think that carrots accounted for the greater part of that number. Wild carrots are also a widespread weed that can commonly be seen growing in disturbed, open habitats such as roadside verges. This post is about the group of plants that carrots typify, the subtribe Daucinae.

Wild carrot Daucus carota in flower, copyright Cwmhiraeth.

Daucinae is a subgroup of the plant family Apiaceae, historically known as the Umbelliferae. The latter name refers to the characteristic production of flowers in dense, flat-topped inflorescences known as umbels. Anyone who is familiar with the appearance of carrot flower-heads is familiar with the form of an umbel; the wild form of carrot is often known as "Queen Anne's lace" in reference to said appearance. The fruit of Apiaceae species is a schizocarp, a dry fruit that splits at maturity into segments (called mericarps), each containing a single seed, that are dispersed independently. In Daucinae and related group of umbellifers, the mericarps carry longitudinal ribs, both primary ribs containing a vascular bundle and secondary ribs without. The secondary ribs of Daucinae are often modified to form broad wings or curved spines that function in the mericarp's dispersal.

Broad-leafed sermountain Laserpitium latifolium seedheads, showing wings, copyright Krzysztof Ziarnek, Kenraiz.

Historically, these differences in mericarp morphology have been used to assign the species bearing them to different tribes. However, more recent phylogenetic analyses have indicated that changes between wings and spines have occurred on multiple occasions due to changes in mode of dispersal (Wojewódzka et al. 2019). Mericarps bearing wings are generally anemochorous (dispersed by wind) whereas those bearing spines are epizoochorous (carried by animals, such as stuck to a mammal's fur). The distinction is not 100% immutable: winged seeds may sometimes get caught in fur, spined seeds may be carried slightly further by wind than smooth ones. Phylogenies indicate that anemochory was the ancestral condition for Daucinae, retained in genera such as Laserpitium and Thapsia. Epizoochorous species do not form a single clade within the Daucinae (indeed, the genus Daucus includes both anemochorous and epizoochorous species) but it is unclear to what degree epizoochory arose on multiple occasions versus reversions to anemochory from epizoochorous ancestors. Two species of Daucinae, Daucus dellacellae from the Cyrenaica region of northern Africa and Cryptotaenia elegans from the Canary Islands, have neither spines nor wings on their mericarps which are therefore dispersed by gravity alone. In the case of C. elegans, at least, it has been suggested that it evolved from epizoochorous ancestors that lost the spines because of the absence of suitable dispersing animals on the islands (Banasiak et al. 2016).

Though the carrot Daucus carota is perhaps the most widely grown daucine umbellifer, it is not the only economically significant member of the group. Cumin Cuminum cyminum, whose seeds are widely used as a spice, is either a daucine or a close relative of daucines (Banasiak et al. 2016). Cuminum does differ from other daucine genera in that its mericarps lack appendages on the secondary keels, however. Gladich Laser trilobum is a perennial found growing in Europe and western Asia whose seeds are used as a condiment. Certain species of the deadly carrot genus Thapsia have a history of medicinal usage though, as their vernacular name suggests, their use does require caution. One species, T. garganica, is among the suggested candidates for the identity of the mysterious silphium of the Romans (used, among other things, as an abortifacient) though perhaps not the most likely contender. That, perhaps, is a story for another time.

REFERENCES

Banasiak, Ł., A. Wojewódzka, J. Baczyński, J.-P. Reduron, M. Piwczyński, R. Kurzyna-Młynik, R. Gutaker, A. Czarnocka-Ciecura, S. Kosmala-Grzechnik & K. Spalik. 2016. Phylogeny of Apiaceae subtribe Daucinae and the taxonomic delineation of its genera. Taxon 65 (3): 563–585.

Wojewódzka, A., J. Baczyński, Ł. Banasiak, S. R. Downie, A. Czarnocka-Ciecura, M. Gierek, K. Frankiewicz & K. Spalik. 2019. Evolutionary shifts in fruit dispersal syndromes in Apiaceae tribe Scandiceae. Plant Systematics and Evolution 305: 401–414.

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 2^nd 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.