Field of Science

Eriogonum spergulinum, the Spurry Buckwheat

Wandering around sandy highlands of the southwest United States, you may encounter a sparse, wiry weed growing between five and forty centimetres in height. This is the spurry buckwheat Eriogonum spergulinum.

Spurry buckwheat Eriogonum spergulinum, copyright Dcrjsr.


Members of the buckwheat family Polygonaceae are found worldwide but tend to be easily overlooked as low, scrubby weeds. In North America, one of the most diverse genera is Eriogonum, known from about 250 species though many are difficult to readily distinguish (Hickman 1993). Eriogonum spergulinum is one of the more recognisable species in the genus. As mentioned above, it grows in sandy soils, particularly those dominated by worn-down granite, and is found at altitudes between 1200 and 3500 metres. It is an annual herb with basal leaves of a linear shape, less than two millimetres wide but up to thirty millimetres long. The greater part of the plant's height is made up by the slender, cyme-like inflorescence bearing unribbed, four-toothed involucres on slender stalks. The flowers are up to three millimetres in diameter with a white perianth marked by darker stripes. Overall, E. spergulinum in flower resembles a drifting cloud of small white stars.

Close-up on Eriogonum spergulinum flowers, copyright Tom Hilton.


Three varieties of Eriogonum spergulinum have been recognised though they are not always distinct and tend to intergrade with each other. In most parts of the species' range, plants belong to the variety E. spergulinum var. reddingianum. This variety is characterised by erect inflorescences with glandular axes and flowers about two millimetres in diameter. The other two varieties are both restricted to the Sierra Nevada mountains of California. Eriogonum spergulinum var spergulinum resembles var. reddingianum but produces larger flowers, about three millimetres in diameter. Eriogonum spergulinum var. pratense is more distinctive. Inflorescences are prostrate to ascending, only about two to five millimetres in height, and lack glands on the axes. Flowers are only 1.5 millimetres across. Pratense is also a higher-altitude variety, found at heights above 2500 metres. The Sierra Nevada varieties are both uncommon; if any variety is likely to be found, it is the widespread reddingianum.

REFERENCE

Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

Scaleyness is Next to Diatom-ness

The last few decades have seen significant advances in our understanding of microbial diversity. Consistent improvements in available technologies and methods for study, both molecular and ultrastructural, have allowed researchers to look further and deeper than they ever could before. Not only have they identified taxa that were previously unknown, they have been able to develop a much better understanding of how microbial taxa relate to each other. Among the fields that has seen particularly remarkable advances has been the study of the picoplankton, that component of the marine plankton comprising organisms less than two or three microns in size. Much of the picoplankton, of course, is made up of bacteria but another significant component is species of microalgae belonging to the group known as heterokonts or stramenopiles.

Schematic diagram of motile bolidophyte cell, from Guillou et al. (1999).


Heterokonts are a major clade of eukaryotes that are commonly characterised by cells bearing anterior pairs of morphologically distinct cilia. One of the cilia is longer and bears rows of hairs referred to as mastigonemes; the other, shorter cilium is usually smooth. Many heterokont species are photosynthetic and belong to a subclade of the heterokonts known as the ochrophytes. For most people, the best known ochrophytes will be the often-decidedly-not-microbial brown algae such as kelps. However, ochrophytes also include a broad diversity of microbial forms. Most ochrophyte cells share a characteristic golden-brown coloration owing to the presence of yellowish pigments such as fucoxanthin as well as the more standard chlorophyll.

Recent molecular studies have supported a division of the ochrophytes between two major clades. On one side are the brown algae and their closer microbial relatives. In the other clade are those ochrophytes more closely related to the diatoms. Appropriately enough, this latter clade was dubbed the Diatomista by Derelle et al. (2016). Other than the diatoms themselves, most representatives of the Diatomista belong to the picoplankton. For the most part, diatoms have lost the cilia otherwise associated with heterokonts. The only exceptions are the reproductive sperm cells which have a single anterior cilium bearing mastigonemes (Adl et al. 2019). The remaining Diatomista commonly have cells bearing one or two anterior cilia (if only one cilium is present, it will typically have mastigonemes). Nevertheless, the basal apparatus of the cilia is reduced, lacking microtubular roots or a rhizoplast, suggestive of an intermediate stage towards total loss (Guillou et al. 1999). Many also bear a covering of silica scales; enlargement of individual scales may have lead to the evolution of diatom-style frustules.

Non-motile cell of Triparma laevis f. inornata, from Kuwata et al. (1987).


The closest known relatives of diatoms are currently classified as the class Bolidophyceae. Motile cells of the Bolidophyceae were first described in 1999 (Guillou et al. 1999). They possessed two cilia, with the haired cilium directed anteriorly and the smooth cilium directed posteriorly, and lacked silica scales. Nevertheless, they were identified as the sister group to diatoms by molecular data. This was corroborated by the absence of a transitional helix structure at the base of each cilium, a feature shared with diatom sperm cells. Guillou et al. (1999) commented on the relatively high mobility of the bolidophytes, in contrast to the general expectation that picoplankton should exhibit a reduction in individual cell mobility owing to the difficulty in meeting energy demands.

The concept of bolidophytes shifted somewhat in the 2010s with the isolation in culture of the Parmales, a group of minute eukaryotes that had first been recognised in the 1980s but had long eluded detailed characterisation. These were non-motile cells enclosed within ornate silica scales. Once molecular data become available, researchers realised that 'Parmales' were not just closely related to 'bolidophytes', they were close enough that the two forms could reasonably be included in a single genus (Kuwata et al. 2018). The exact details of their connection, however, remain uncertain. It seems likely that the flagellate and non-flagellate forms represent alternate forms of single species. But whether we are looking at alternate generations of the life cycle, or whether the flagellate cells are generated in response to particular conditions, remains to be determined.

Skeleton of silicoflagellate Dictyocha speculum, copyright Proyecto Agua.


The remaining members of the Diatomista form a clade currently treated as including three classes, the Dictyochophyceae, Pelagophyceae and Pinguiophyceae. Together they are a diverse array of minute organisms, whether ciliated or amoeboid, naked or carrying organic scales, photosynthetic or heterotrophic or some combination of both. Among the representatives of the Dictyochophyceae are the so-called silicoflagellates, ciliated cells reinforced with a skeleton of (duh) silica. Though only a few species of silicoflagellate are recognised in the modern environment, they have an extensive fossil record extending back to the Middle Cretaceous (Kristiansen 1990). In some places, their preserved skeletons may dominate rock formations. Silicoflagellates appear to have reached their peak in the Miocene, followed by a decline to their modern condition. The exact interpretation of the silicoflagellate fossil record is a long-standing challenge (whether differences in morphology are taxonomic or environmental, for instance) but they hold the potential to tell us much about the history of our seas.

REFERENCES

Adl, S. M., D. Bass, C. E. Lane, J. Lukeš, C. L. Schoch, A. Smirnov, S. Agatha, C. Berney, M. W. Brown, F. Burki, P. Cárdenas, I. Čepička, L. Chistyakova, J. del Campo, M. Dunthorn, B. Edvardsen, Y. Eglit, L. Guillou, V. Hampl, A. A. Heiss, M. Hoppenrath, T. Y. James, A. Karnkowska, S. Karpov, E. Kim, M. Kolisko, A. Kudryavtsev, D. J. G. Lahr, E. Lara, L. Le Gall, D. H. Lynn, D. G. Mann, R. Massana, E. A. D. Mitchell, C. Morrow, J. S. Park, J. W. Pawlowski, M. J. Powell, D. J. Richter, S. Rueckert, L. Shadwick, S. Shimano, F. W. Spiegel, G. Torruella, N. Youssef, V. Zlatogursky & Q. Zhang. 2019. Revisions to the classification, nomenclature, and diversity of eukaryotes. Journal of Eukaryotic Microbiology 66: 4–119.

Derelle, R., P. López-García, H. Timpano & D. Moreira. 2016. A phylogenomic framework to study the diversity and evolution of stramenopiles (=heterokonts). Molecular Biology and Evolution 33 (11): 2890–2898.

Guillou, L., M.-J. Chrétiennot-Dinet, L. K. Medlin, H. Claustre, S. Loiseaux-de Goër & D. Vaulot. 1999. Bolidomonas: a new genus with two species belonging to a new algal class, the Bolidophyceae (Heterokonta). Journal of Phycology 35: 368–381.

Kristiansen, J. 1990. Phylum Chrysophyta. In: Margulis, L., J. O. Corliss, M. Melkonian & D. J. Chapman (eds) Handbook of Protoctista. The structure, cultivation, habitats and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. A guide to the algae, ciliates, foraminifera, sporozoa, water molds, slime molds and the other protoctists pp. 438–453. Jones & Bartlett Publishers: Boston. Kuwata, A., K. Yamada, M. Ichinomiya, S. Yoshikawa, M. Tragin, D. Vaulot & A. Lopes de Santos. 2018. Bolidophyceae, a sister picoplanktonic group of diatoms—a review. Frontiers in Marine Science 5: 370.

Glyphyalinia Snails

North America (as with pretty much everywhere in the world outside the coldest regions) is home to a wide diversity of small, terrestrial snails that tend to pass unnoticed. Among the more diverse of these is the zonitid genus Glyphyalinia.

Glyphyalinia carolinensis, copyright John Slapcinsky.


Glyphyalinia species are often found in forest leaf-litter in the eastern part of North America. They have a low, translucent shell that is often about half a centimetre in diameter. Whorls of the shell increase regularly in size and are marked by a series of strongly impressed radiating lines in addition to finer growth lines. The umbilicus of the shell varies between species from completely absent to quite wide (Burch & Pearce 1990). The soft body of the animal varies in coloration, again depending on species. That of G. roemeri is all white except for the eyes; that of G. wheatleyi is almost uniformly black. The reproductive system of Glyphyalinia (which are hermaphroditic) includes a well-developed epiphallus and a distinct, ovoid spermathecal sac (Baker 1930).

Multiple species of Glyphyalinia may be found living in a single patch of forest though, at present, we know little about how (and whether) micro-habitats are partitioned between species. Some species seem to tolerate a wide variety of soil types and are correspondingly widely distributed. Others are more selective and localised; some may be considered endangered by habitat degradation. Even supposedly widespread species may be more vulnerable than appreciated: at least some may represent clusters of closely related species rather than truly uniform populations. These tiny snails can be notoriously difficult to study, making for a risk that they might just slip away barely noticed.

REFERENCES

Baker, H. B. 1930. The North American Retinellae. Proceedings of the Academy of Natural Sciences of Philadelphia 82: 193–219.

Burch, J. B., & T. A. Pearce. 1990. Terrestrial Gastropoda. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 201–309. John Wiley & Sones: New York.

Williamsita

A while back, I wrote a post about the crabronid wasp genus Podagritus. This time, I'm going to cover another crabronid genus found here in Australia: Williamsita.

Williamsita sp., copyright David Francis.


Like Podagritus, Williamsita species are boldly coloured wasps, typically mostly black with contrasting yellow or orange markings. They differ from Podagritus species in being more robust with the base of the gaster not notably pedunculate. Other distinguishing features include the presence of distinct foveae (pits) against the margins of the eyes (occasionally less distinct in males), thirteen-segmented antennae in males, and a pygidial plate in both sexes that is narrowed and concave in females, quadrate in males. Williamsita species also do not have the palps reduced as in Podagritus, instead having the more typical arrangement of six segments in the maxillary palps and four segments in the labial palps (Bohart & Menke 1976).

To date, eleven species have been recognised in the genus Williamsita (Leclercq 2006). Most are found in Australia with a single species each known from New Caledonia and Vanuatu. Leclercq (1950) suggested dividing the genus between two subgenera with all species except the New Caledonian type species W. novocaledonica forming a subgenus Androcrabro. Features supporting the latter taxon included the presence of ventral notches on one or more segments of the antennae in males. However, Leclercq later suggested abandoning such a formal division, questioning its significance (Leclercq 2006). The Australian species of Williamsita are, nevertheless, distinct from the two insular species in being marked with much stronger punctation over the body.

Most Williamsita species remain little seen and poorly known. However, breeding habits have been recorded for two Australian species, W. bivittata and W. tasmanica (Maynard & Fearn 2021; McCorquodale et al. 1989). Both these species nest in branching holes in rotting wood, either commandeering burrows left by wood-boring insects or excavating their own. Prey consists of larger flies such as blow flies or soldier flies which were carried back to the nest by the wasp running with the fly carried below the body. Up to six paralysed flies might be placed lying on their backs in a nest cell with an egg laid across the 'throat' (i.e. at the joint between head and thorax) of one of the flies. The cell would then be closed with a plug of woody frass. McCorquodale et al. (1989) recorded W. bivittata constructing several such cells in a series along a single tunnel, whereas Maynard & Fearn (2021) found W. tasmanica more likely to place a single cell in a side-branch. As both observations were limited to a single location in a single season, though, one might reasonably question whether these represent true differences in species behaviour or were determined by available conditions. There's a limit to how deep a Williamsita can burrow.

REFERENCES

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

Leclercq, J. 1950. Sur les crabroniens orientaux et australiens rangés par R. E. Turner (1912–1915) dans le genre Crabro (subgenus Solenius). Bulletin et Annales de la Société Entomologique de Belgique 86 (7–8): 191–198.

Leclercq, J. 2006. Hyménoptères crabroniens d'Australie du genre Williamsita Pate, 1947 (Hymenoptera: Crabronidae). Notes Fauniques de Gembloux 59 (2): 115–119.

Maynard, D., & S. Fearn. 2021. Ecological and behavioural observations of a nesting aggregation of the endemic Tasmanian digger wasp Williamsita tasmanica (Smith, 1856) (Hymenoptera: Crabronidae: Crabroninae). Papers and Proceedings of the Royal Society of Tasmania 155 (1): 43–50.

McCorquodale, D. B., C. E. Thomson & V. Elder. 1989. Nest and prey of Williamsita bivittata (Turner) (Hymenoptera: Sphecidae: Crabroninae). Australian Entomological Magazine 16 (1): 5–8.

Opening Dors

My current dayjob mostly revolves around identifying and counting dung beetles. When Europeans settled Australia, they brought their farm animals with them. Unfortunately, the large piles of dung produced by cattle and horses proved rather daunting to native scavengers used to the more compact droppings of kangaroos and possums. And if you've ever experienced an Australian summer, you'll know that flies are definitely a thing. To help with this situation, Australia has had a long-running programme introducing exotic dung beetles that are better able to clean up after livestock. Most of these are members of the typical dung beetle family Scarabaeidae but one species, Geotrupes spiniger, represents a different subgroup of the superfamily Scarabaeoidea. These are the earth-boring dung beetles or dor beetles of the Geotrupidae.

Dor beetle Geotrupes spiniger, copyright Udo Schmidt.

The geotrupids are medium-sized to very large beetles, ranging in size from half a centimetre to 4.5 cm in length (Jameson 2002). Like many other members of the Scarabaeoidea, they have broad fore legs used for digging. Their short, eleven-segmented antennae end in the asymmetrical club typical of scarabaeoids but they may be distinguished from other families in that the basal segment of the three-segmented club is expanded to form a 'cup' against which the other segments may be tightly closed. The body of geotrupids is strongly convex, and is smooth and shiny dorsally but hairy underneath. In many species, the males may bear elaborate horns and/or processes on the head and pronotum.

Male Taurocerastes patagonicus, copyright Nicolás Lavandero.


Despite their size, geotrupids are secretive animals, spending most of their time in burrows underground (which may be up to three metres in depth) and usually only emerging at night. Various species feed on animal dung or decaying matter; some feed on subterranean fungi. In at least some species, eggs are laid in brood chambers within the parent's home burrow and multiple life stages may share a single burrow. Burrows may also be shared between multiple adults when conditions demand. Though adults do not directly tend to larvae, they may stock brood chambers with food supplies. In some Australian species of the subfamily Bolboceratinae, females lay a single gigantic egg at a time that may be up to 56% the size of its layer (Houston 2011). Larvae hatching from such an egg are able to develop right through to maturity without feeding.

Adult geotrupids produce a stridulating noise when disturbed which is the origin of the alternate vernacular name of "dor beetle" ("dor" being an old word for a buzzing insect). Larvae may or may not be capable of stridulation, depending on the species.

Male Blackburnium rhinoceros, copyright Edward Bell.


The classification of geotrupids is the subject of ongoing investigation. A recent classification divides the family between three subfamilies, the widespread Geotrupinae and Bolboceratinae and the South American Taurocerastinae. Morphological differences between these subfamilies, particularly at the larval stage, have lead some researchers to question whether the Geotrupidae in the broad sense represents a monophyletic group. Molecular analyses thus far seem ambiguous; an analysis by McKenna et al. (2015) placed geotrupids as part of a polytomy near the base of the scarabaeoids. As an aside, my supervisor recently asked myself and a retired colleague whether Geotrupes spiniger was the only species of geotrupid found in Australia. I replied "yes", our colleague responded "no". Our conflict, of course, was based on whether Australia's wide diversity of Bolboceratinae contributed to the count.

REFERENCES

Houston, T. F. 2011. Egg gigantism in some Australian earth-borer beetles (Coleoptera: Geotrupidae: Bolboceratinae) and its apparent association with reduction or elimination of larval feeding. Australian Journal of Entomology 50: 164–173.

Jameson, M. L. 2002. Geotrupidae Latreille 1802. In: Arnett, R. H., Jr, M. C. Thomas, P. E. Skelley & J. H. Frank (eds) American Beetles vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea pp. 23–27. CRC Press.

McKenna, D. D., B. D. Farrell, M. S. Caterino, C. W. Farnum, D. C. Hawks, D. R. Maddison, A. E. Seago, A. E. Z. Short, A. F. Newton & M. K. Thayer. 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40: 35–60.

Platybunus: the Wide-Eyed Harvestmen of Europe

The western Palaearctic region (that is, Europe and the immediately adjacent parts of Asia and northern Africa) is home to a diverse and distinctive fauna of harvestmen. Among the various genera unique to this part of the world are the forest- and mountain-dwellers of the genus Platybunus.

Platybunus pinetorum, copyright Donald Hobern.


Platybunus species are moderate-sized long-legged harvestmen of the family Phalangiidae, the central body in larger individuals being about eight millimetres long (Martens 1978). Their most characteristic feature is a relatively large eye-mound, distinctly wider than long and occupying a large section of the anterior carapace. As with other European phalangiids, they eye-mound is ornamented with a row of denticles each side though the body lacks denticles over the remainder of the dorsum. The body is often comparatively slender, tapering towards the rear (particularly in males), and is marked on the dorsum by a darker median band. The pedipalps have a pair of well-developed setose apophyses on the inner distal ends of the patella and tibia, and a series of long spine-like tubercles on the underside of the femur. These tubercles presumably function in the capture of prey, forming a basket that can be closed around the harvestman's victims. External sexual dimorphism in Platybunus is fairly minimal though females are overall larger and fatter. The penis is notably long and slender with a relatively small glans, offset from the shaft by a more or less marked constriction.

Platybunus bucephalus, copyright Adrian Tync.


Martens (1978) recognises four species of Platybunus found in higher altitude regions of central Europe with the species P. bucephalus and P. pinetorum occupying much of the genus' range. Platybunus bucephalus may be distinguished from P. pinetorum by, among other features, its relatively shorter legs. Platybunus pallidus is endemic to the Carpathians, and the tiny P. alpinorelictus inhabits the Garda Mountains of northern Italy. Another species, P. anatolicus, was described from Turkey by Roewer (1956)*. In general, Platybunus species inhabit alpine and subalpine forests, being found among the herbaceous undergrowth, under bark or on rock faces. Where their ranges overlap, P. bucephalus is more accustomed to extending beyond the forest margins than P. pinetorum and may be found above the tree-line. In recent years, the range of P. pinetorum has extended northwards, being first recorded from the UK in 2010 and Sweden in 2015 (Fritzén et al. 2015). At least some populations of P. pinetorum are capable of reproducing parthenogenetically and this may have played a part in its spread.

*Platybunus mirus was described by Loman (1892) on the basis of two male specimens that supposedly came from Sumatra. Though the identity of this species has never been resolved (Loman's illustration of the penis is at least suggestive of a true Platybunus), the claimed locality seems almost certain to be an error of some kind.

The internal classification of the Phalangiidae remains in need of further investigation. Platybunus has been recognised by some authors as forming a subfamily Platybuninae with a cluster of other western Palaearctic genera bearing similar ventrally spined pedipalps (Zhang & Zhang 2012). However, other authors have not separated this group from the subfamily Phalangiinae. The platybunines may represent a phylogenetically coherent grouping, or their shared features may reflect adaptations to a similar life style. The genital morphology of Platybunus is recognisably distinct from that of other platybunines which may argue against any relationship (Martens 1978). On the other hand, platybunines might possibly be distinguished from phalangiines by the chemical composition of their repugnatorial gland secretions (Raspotnig et al. 2015). A formal analysis of the family's evolution would be a welcome advance.

REFERENCES

Fritzén, N. R., V. Rinne, M. Sunhede, A. Uddström, S. Van de Poel & P. De Smedt. 2015. Platybunus pinetorum (Arachnida, Opiliones) new to Sweden. Memoranda Soc. Fauna Flora Fennica 91: 37–40.

Loman, J. C. C. 1892. Opilioniden von Sumatra, Java und Flores. In: M. Weber (ed.) Zoologische Ergebnisse einer Reise in Niederländisch Ost-Indien vol. 3 pp. 1–26, pl. 1. E. J. Brill: Leiden.

Martens, J. 1978. Spinnentiere, Arachnida: Weberknechte, Opiliones. Gustav Fischer Verlag: Jena.

Raspotnig, G., M. Schaider, P. Föttinger, V. Leutgeb & C. Komposch. 2015. Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis. Chemoecology 25: 63–72.

Roewer, C. F. 1956. Über Phalangiinae (Phalangiidae, Opiliones Palpatores). (Weitere Weberknechte XIX). Senckenbergiana Biologica 37 (3–4): 247–318.

Zhang, C., & F. Zhang. 2012. On the subfamilial assignment of Platybunoides (Opiliones: Eupnoi: Phalangiidae), with the description of a new species from China. Zootaxa 3190: 47–55.

Voley, Voley, Voley

Over a third of all living mammal species are rodents. In cooler regions of the Northern Hemisphere, the rodent fauna is often dominated by the Microtinae, the group of mouse-like rodents including voles and lemmings. And in North America, the most widespread of all microtine species is the eastern meadow vole Microtus pennsylvanicus.

Eastern meadow vole Microtus pennsylvanicus, copyright Gilles Gonthier.


The eastern meadow vole is found over most of Canada and a large part of the northern and eastern United States, with the subspecies M. p. chihuahuensis known from Chihuahua in northern Mexico. This species is about the size of a small rat, being from 14 to 20 cm in length with about three to six centimentres of that length being tail (Reich 1981). They are generally yellowish-brown in colour with black tips on the hairs though individuals vary significantly in brightness and shade. Western populations are supposed to be lighter in coloration than eastern, and southern individuals tend to be larger than northern. As an indication of this species' variability, Reich (1981) recognised 28 recognised subspecies.

Eastern meadow voles are primarily inhabitants of grasslands, with a preference for damper habitats, though they may also be found in woodlands. They mostly live in burrows underground, emerging to the surface to forage for food. Eastern meadow voles are generalist feeders, browsing on most available forms of low vegetation: grasses, sedges and herbs. When populations reach their peak, they may cause significant damage to woody plants by ringbarking their trunks. Individuals may seemingly be active at just about any time of day.

Eastern meadow vole in a state of danger, copyright David Allen.


Like other small rodents, meadow voles are short-lived animals with estimates of average lifespan ranging from just two or three months to ten to fourteen months (Reich 1981). Studies of movement patterns indicate that mature females generally maintain distinct, non-overlapping ranges whereas males range further and with less concern for others (Madison 1980). Mating behaviour appears generally promiscuous: males will range over the territories of multiple females and litters with mixed paternity are not uncommon (Boonstra et al. 1993). Paternal behaviour has been observed among eastern meadow voles in laboratory populations but all indications are that wild males do not remain with females after mating. Males often bear wounds indicative of intra-species conflict. These may be the result of males fighting over access to females but Madison (1980) suggested a potential alternative. Less dominant males might be more likely to attempt to approach females earlier or later in their oestrus cycle as the females are more likely to be guarded by dominant males when at their peak. While avoiding attacks from their dominant brethren, these minor males might find themselves violently rebuffed by a female who is just not yet in the mood.

After mating, gestation lasts for about three weeks, usually resulting in a litter of four to six babies. Weaning then takes place after about two weeks. Females forage far less while lactating than at other times. It might seem counter-intuitive for a female to reduce feeding when her energy demands are presumably at their peak but again Madison (1980) suggests an explanation: perhaps her energy needs are such that she simply lacks the capacity for extensive wandering. Young may potentially remain with their mother for some time after weaning but eventually they will be forced out of the parental burrow, leaving to face the wide world on their own. And when you're the size of a vole, that's a very wide world indeed.

REFERENCES

Boonstra, R., X. Xia & L. Pavone. 1993. Mating system of the meadow vole, Microtus pennsylvanicus. Behavioral Ecology 4: 83–89.

Madison, D. M. 1980. Space use and social structure in meadow voles, Microtus pennsylvanicus. Behavioral Ecology and Sociobiology 7: 65–71.

Reich, L. M. 1981. Microtus pennsylvanicus. Mammalian Species 159: 1–8.

Anchor Sponges

Sponges are, by their very nature, a challenging group taxonomically. At the macroscopic level, they are often amorphous and indeterminate in appearance. As one taxonomist complained in 1842 (as quoted in Hooper & Van Soest 2002): "there is so much that is in common to them, and each adapts itself so readily to circumstances and assumes a new mask, that it requires a tact, to be gained only by some experience, to recognize them under their guises; while we labour, perhaps in vain, to devise phrases which shall aptly portray to others the characteristics of objects that have no fixed shape, and whose distinctive peculiarities almost cheat the eye". Reliable identification typically requires the close examination of microscopic details, in particular the conformation and arrangement of the mineralised spicules that make up the skeleton of many sponges.

Myxilla incrustans, copyright B. E. Picton.


The Myxillidae are a family of marine sponges that, so far as we currently know, are most diverse in temperate and frigid waters. Like other members of the class Demospongiae, the most diverse of the recognised sponge classes, they have a skeleton of spicules constructed from silica. Different arrangements of spicules allow the body of the sponge to be divided into two layers. In the outer ectosoma, which can be thought of as the 'skin' of the sponge, elongate spicules are vertically radiating or placed in 'bouquet' arrangements with a palisade of vertical spicules surmounted by radiating clusters. These spicules generally have each end similar and may be smooth or spiky. In the inner choanosoma, within which are placed the feeding chambers of the sponge, elongate spicules are placed in a reticulate arrangement. These spicules generally have one end pointed and the other blunt.

Skeletal arrangements and individual spicules from various Myxillidae, from Hooper & Van Soest (2002).


Mixed in amongst these larger megasclere spicules are smaller microscleres that do not form part of the main structural skeleton, though presumably they do help hold the sponge body together. In myxillids, the microscleres generally take the form of anchorate chelae, small curved structures with incurved rounded prongs at each end. Members of the boreal genus Melonanchora have a mixture of chelae and a different type of microsclere shaped like a ribbed rugby ball (Santín et al. 2021). In the Indo-West Pacific genus Psammochela, growing sponges will also incorporate sand from the surrounding environment to supplement the microscleres (de Voogd 2012).

Growth habit of Myxillidae can vary from encrusting to massive to branching. The species Stelodoryx procera, found around the Azores, has a distinctive growth habit with a flattened main body at the end of an elongate stalk. On the whole, though individual species may be distinguished by growth habit, species within a single genus may differ greatly in form. For determining genera, examination of spicules is really the only way to go.

REFERENCES

Hooper, J. N. A., & R. W. M. Van Soest. 2002. Systema Porifera: A guide to the classification of sponges vol. 1. Kluwer Academic/Plenum Publishers.

Santín, A., M.-J. Uriz, J. Cristobo, J. R. Xavier & P. Ríos. 2021. Unique spicules may confound species differentiation: taxonomy and biogeography of Melonanchora Carter, 1874 and two new related genera (Myxillidae: Poecilosclerida) from the Okhotsk Sea. PeerJ 9: e12515.

Voogd, N. J. de. 2012. On sand-bearing myxillid sponges, with a description of Psammochela tutiae sp. nov. (Poecilosclerida, Myxillina) from the northern Moluccas, Indonesia. Zootaxa 3155: 21–28.

Succulent Orchids

With over 1200 known species found in Asia and Australasia, Dendrobium is one of the largest currently recognised genera of orchids. As with other examples of such 'super-genera', the question of how to best handle such a monster has been fiercely debated. In 2003, Australian botanist M. Clements proposed dividing Dendrobium between numerous segregate genera, noting (among other reasons) that the genus as previously recognised was not monophyletic. However, Clements' system does not seem to have garnered widespread usage with other orchid systematists preferring to retain a broad concept of Dendrobium (excluding some of the more egregious outliers) that largely corresponds with its established usage (e.g. Schuiteman 2011). Nevertheless, many of the subdivisions promoted by Clements remain recognised as well delimited groups. One such cluster is the assemblage of species recognised as Dendrobium section Aporum.

Growth habit of Dendrobium sect. Aporum, copyright Tony Rodd.


Species of section Aporum are epiphytes found in lowland forests of south-east Asia, extending eastwards to New Guinea and the Solomon Islands. Members of this section have thin stems that are erect at first but tend to become pendulous as they lengthen. Leaves are fleshy and equitant: that is, they are folded longitudinally with what would otherwise be the two sides of the dorsal surface fused, except at the base where they overlap with opposing leaves. The stem may be more or less completely concealed by the leaf bases. Tips of the leaves end in a point. Flowers are borne singly or in clusters, arising laterally on the stem between leaf nodes or at the tip of the stem alongside a terminal scale. The flowers may be subtended by persistent chaffy bracts. They are generally small and fleshy and tend to be short-lived, wilting after just a few days.

Flowers of Dendrobium anceps, copyright Aqiao HQ.


The functional significance of the Aporum section's distinctive leaves remains uncertain. As noted by Carlsward et al. (1997), the fleshy leaves might be taken as an adaptation to water retention. However, though access to water is a consistent concern for epiphytes, the humid rainforests in which Aporum species are found hardly seem the driest of places. Conversely, the effective even distribution of stomata on both sides of leaf resulting from their equitant condition may make it easier for excess water to be released from the plant.

Dendrobium distichum, photographed by Ronny Boos.


Orchids in general are, of course, most often considered by people as ornamental plants. My impression is that the various Aporum species tend not to be among the most widely grown of species though their unusual growth habit might attract interest. This may be due to them not being the easiest of orchids to maintain; they appear to require high humidity and warm temperatures to thrive with a cooler, drier period in the non-growing season. Among the more popular species are Dendrobium anceps and D. keithii, both of which produce small greenish flowers. Those of D. anceps have been described as having a distinct "apple pie" fragrance. Of course, if you happen to be wandering through the jungles of south-east Asia, you might well discover these plants growing of their own accord.

REFERENCES

Carlsward, B. S., W. L. Stern, W. S. Judd & T. W. Lucansky. 1997. Comparative leaf anatomy and systematics in Dendrobium, sections Aporum and Rhizobium (Orchidaceae). International Journal of Plant Sciences 158 (3): 332–342.

Clements, M. A. 2003. Molecular phylogenetic systematics in the Dendrobiinae (Orchidaceae), with emphasis on Dendrobium section Pedilonum. Telopea 10 (1): 247–298.

Schuiteman, A. 2011. Dendrobium (Orchidaceae): to split or not to split? Gardens' Bulletin Singapore 63 (1–2): 245–257.

The Huenellidae

Researchers who deal with the modern marine fauna are used to thinking of brachiopods as a marginal group, their diversity greatly overshadowed on a global scale by the superficially similar bivalves. However, modern brachiopods are but a shadow of their former selves; for much of the Palaeozoic era, their relationship with the bivalves was the inverse of today. Many are the brachiopod lineages that came and went over this time.

External views of ventral (left) and dorsal valves of Huenella triplicata, from Walcott (1924).


The Huenellidae were an assemblage of brachiopods that lived during the late Cambrian and early Ordovician (Amsden & Biernat 1965). They represent early representatives of the Pentamerida, a Palaeozoic order of fairly generalised-looking brachiopods. Within the Pentamerida, they fall within the suborder Syntrophiidina. Syntrophiidinans as a whole are rarely found in the fossil record and as a result remain poorly known. Members of the suborder share a distinctive shape with biconvex valves marked by a dorsal fold and ventral sulcus. That is, the midline of the shell is raised above either side with the ventral valve forming a 'valley' to match the raised 'hill' of the dorsal valve. What, if anything, was the purpose of this arrangement I wouldn't know but modern brachiopods often inhabit locations with a lot of organic silt and/or fine sediment. Perhaps the uneven level of the syntrophiidinan shell helped protect it from burial by a shifting substrate.

Interior view of ventral valve of Radkeina taylori, from Laurie (1997), with scoop-shaped spondylium at upper midline.


Families of Syntrophiidina may be distinguished based on the development of the spondylium, an internal projection at the base of the ventral valve that provided an attachment site for the shell muscles. Members of the Huenellidae possessed either a sessile spondylium or a pseudospondylium, a spondylium-type structure rising from the internal surface of the valve itself rather than from the hinge. Amsden & Biernat (1965) recognised a division of the huenellids between two subfamilies based on the development of the brachiophore plates, projections on the inside of the dorsal valve that would have supported the lophophore. Members of the Huenellinae possessed more developed brachiophores than members of the Mesonomiinae. Outer ornament of the huenellid shell varied from more or less smooth with weak concentric ridges to costate with distinct radiating ridges.

Phylogenetic relationships within the Syntrophiidina do not seem to have been established in detail but the early appearance in the fossil record of huenellids at least raises the question of whether they included the ancestors of later families. As well as other families of the Syntrophiidina, candidates for descent would include members of the suborder Pentameridina as well as of the related order Rhynchonellida. This latter order includes species which survive to the present day so the possibility exists that while the huenellids themselves may be long gone, their legacy may yet live on.

REFERENCE

Amsden, T. W., & G. Biernat. 1965. Pentamerida. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt H. Brachiopoda vol. 2 pp. H523–H552. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas Press: Lawrence (Kansas).

Arranging Nautiloids

For years, the higher taxonomy of cephalopods was expressed as a division between three subclasses: the Nautiloidea, the Ammonoidea and the Coleoidea. Coleoids were the clade of cephalopods that had lost the external shell, ammonoids were a Mesozoic lineage with complex septa dividing the chambers of the shell, and nautiloids were... the rest. From the tiny, possibly benthic, curved cones of the Cambrian where the class began, to gigantic straight-shelled monsters of the later Palaeozoic, to the modern chambered nautilus, all were lumped together as 'nautiloids'. The nautiloid subclass was explicitly understood to include the ancestors of the others but recognition of more phylogenetically coherent subgroups has been hampered by poor understanding about how the various nautiloid lineages were interrelated. And part of the problem in this regard has been uncertainty about just what features of their fossils we should be paying attention to.

Diorama reconstruction of Beloitoceras oncocerids, from the Burpee Museum.


One factor that has drawn attention in recent years has been the arrangement of muscle scars on the shell. Large muscle attachment scars appear as raised annular elevations on the inside of the shell towards the rear end of the body chamber (in practice, they are more often observed in fossils as depressions on the internal mould). In the living nautilus, the muscles attached to these scars function in the retraction of the head (King & Evans 2019). Modern nautilus possess a pair of large lateral scars in an arrangement that has been labelled 'pleuromyarian'. However, many of the earliest cephalopods possessed a ring of numerous small scars, an arrangement referred to as 'oncomyarian'. Other cephalopods might have scars restricted to the dorsal ('dorsomyarian') or ventral ('ventromyarian') midline.

Primary types of muscle scar in nautiloids, from King & Evans (2019). 'D' and 'V' indicate dorsal and ventral, respectively, and arrows indicate direction of aperture.


Another feature that has been called out has been the structure of the connecting rings around the siphuncle. Shelled cephalopods, you will recall, have the shell divided into chambers separated by septa. Though the bulk of the animal is found in the final body chamber, a fleshy cord called the siphuncle runs back through the remaining chambers. In life, the siphuncle is used to control the levels of fluid in the chambers, which in turn controls the animal's buoyancy. The boundary between the siphuncle and the surrounding chamber is marked a toughened sheath, referred to as the connecting ring. In the modern nautilus, the connecting ring is comprised of two layers, an outer calcareous layer and an inner chitinous layer. In comparable fossils, the latter chitinous layer has decomposed after death so only the outer layer is preserved. However, some extinct cephalopod groups preserve evidence of calcification in the inner as well as the outer layer. Based on the distinction between these two siphuncle types, Mutvei (2015) supported dividing most of the nautiloids between two major lineages, the Nautilosiphonata (with a nautilus-type siphuncle) and the Calciosiphonata (with the internally calcified connecting rings).

A couple of years earlier, the same author (Mutvei 2013) had proposed recognition of a superorder Multiceratoidea for nautiloids that combined multiple muscle scars with a nautilus-type siphuncle. Examples of nautiloid orders with such a combination included the Ellesmeroceratida (small nautiloids with densely placed septa), the Oncoceratida (often short, squat nautiloids) and the Discosorida (similarly squat forms with complex bulging connecting rings). All of these were found in the earlier part of the Palaeozoic with the oncoceratids dieing off in the early Carboniferous. Mutvei (2013) also included the coiled Tarphyceratida and the egg-shaped Ascoceratida in this group. Later, King & Evans (2019) redefined this grouping as the Multiceratia, excluding the Tarphyceratida and Ascoceratida on the grounds that they had ventromyarian rather than oncomyarian muscle scars. Mutvei (2013) suggested that, rather than representing retractor muscles, these smaller repeated scars were associated with an outgrowth of the mantle, either as tentacles or a muscular 'skirt', that was used to capture micro-plankton.

Phylogeny of 'nautiloids' supported by King & Evans (2019). Though not shown on this diagram, the majority of authors have suggested that ammonoids and coleoids are descended from Orthoceratida.


King & Evans (2019) proposed a reclassification of the subclass Nautiloidea between five subclasses defined primarily by muscle structure. Apart from the earliest oncomyarian Plectronoceratia, most 'nautiloids' could be divided between two lineages. On one side were the dorsomyarian Orthoceratia (usually thought to include the ancestors of the ammonoids and coleoids). On the other, the oncomyarian Multiceratia would eventually give rise to the ventromyarian Tarphyceratia which in turn included the ancestors of the pleuromyarian Nautilida. Note that many of the reocognised subclasses (and orders) remain paraphyletic but we are at least approaching a more informative picture of cephalopod evolution than the earlier unceremonious dumping into 'Nautiloidea' (I should probably also remind you that, for various reasons, most invertebrate palaeontologists still don't regard strict monophyly as a taxonomic requirement in and of itself).

The usage of muscle scars and connecting rings as classificatory keys is handicapped by the difficulty of observing them. As internal structures, they each require careful preparation of a specimen to observe. And once you've gotten to a position where you can see them, it seems not to be particularly easy to tell just what you're looking at. As a result, muscle scarring and siphon structure remains undescribed for the majority of nautiloid species. Judging the structure of connecting rings seems to be particularly challenging and some have gone so far as to suggest that purported different structures may be the result of post-mortem taphonomic processes (King & Evans 2019). Nevertheless, what we do know suggests that such features remain reasonably consistent within each of the well-recognised nautiloid orders. And Mutvei's (2015) concept of Calciosiphonata vs Nautilosiphonata does largely line up with King & Evans' (2019) dorsomyarian vs oncomyarian-ventromyarian lineages. There are, of course, some notable exceptions. Whether these will cause the developing structure to collapse, or whether they indicate mistakes in interpretation, only continued research will tell.

REFERENCES

King, A. H., & D. H. Evans. 2019. High-level classification of the nautiloid cephalopods: a proposal for the revision of the Treatise Part K. Swiss Journal of Palaeontology 138: 65–85.

Mutvei, H. 2013. Characterization of nautiloid orders Ellesmerocerida, Oncocerida, Tarphycerida, Discosorida and Ascocerida: new superorder Multiceratoidea. GFF 135 (2): 171–183.

Mutvei, H. 2015. Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloid Bathmoceras (Cephalopoda). GFF 137 (3): 164–174.

A Brief Spotlight on Scopariines

The moths of the Pyraloidea are perhaps one of the more under-appreciated sectors of lepidopteran diversity. With many thousands of species, they comprise a significant proportion of the order in terms of both taxonomic and ecological diversity. Nevertheless, with most species being small and dull in coloration, many Lepidoptera enthusiasts will tend to lump them in the too-hard basket for study. One subgroup of the pyraloids to which this issue definitely applies is the subfamily Scopariinae.

Scoparia spelaea, copyright Donald Hobern.


Close to 600 species of Scopariinae are known from around the world with the highest diversity found on tropical mountains and islands (Léger et al. 2019). They are mostly a mottled greyish in coloration, blending in among the rocks and tree trunks on which they settle during the day. Like other pyraloids, they have large palps that extend in front of the head; pyraloids as a whole are sometimes referred to as 'snout moths' in reference to the appearance this gives them. Forewing venation is characterised by clear separation of vein R2 from R3+4 and absence of CuP (Nielsen & Common 1991).

Meadow grey Scoparia pyralella, copyright Hectonichus.


The majority of scopariine species feed as larvae on mosses, living concealed within a slight silk web. A smaller number feed on dicotyledons or lichens. One New Zealand species, the sod webworm Eudonia sabulosella, has been known to cause economic damage to pasture during sporadic outbreaks. Other species generally do not cause significant impact to humans.

Eudonia lacustrata, copyright Tony Morris.


Identification of scopariines is notoriously difficult with many species closely approximating each other in pattern or exhibiting confounding intra-specific variation. The two largest genera Scoparia and Eudonia can only be reliably separated by examination of the genitalia. Two genera, the Indo-Australian Micraglossa and the Neotropical Gibeauxia, are distinguished by the presence of shiny golden scales on head, thorax and abdomen. With such significant challenges to their study, it would not be surprising if 600 species should turn out to be a marked under-estimate of their true diversity.

REFERENCES

Léger, T., B. Landry & M. Nuss. 2019. Phylogeny, character evolution and tribal classification in Crambinae and Scopariinae (Lepidoptera, Crambidae). Systematic Entomology 44: 757–776.

Nielsen, E. S., & I. F. B. Common. 1991. Lepidoptera (moths and butterflies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 817–915. Melbourne University Press: Carlton (Victoria).

Psalidothrips

Many of you may know thrips as small insects that infest buds and young shoots of garden plants, stymieing growth and causing malformed development. However, there is also a wide diversity of thrips species that feed on fungi, inhabiting leaf litter and other fallen vegetation. In tropical and subtropical regions of the world, one of the more numerous genera of such fungus-feeders is Psalidothrips.

Winged female (left) and wingless male of Psalidothrips comosus, from Zhao et al. (2018).


Close to fifty species of Psalidothrips have been described from various locations around the world (Wang et al. 2019). They are most commonly found among leaf litter and are believed to feed on fungal hyphae. Most Psalidothrips are relatively small, pale thrips, yellowish or light brown in coloration. As members of the family Phlaeothripidae, the last segment of the abdomen is modified into a tube ending in a ring of setae; in Psalidothrips, this tube is commonly short and the terminal setae are often longer than the tube.

As is common among thrips, the recognition of Psalidothrips and its constituent species is often complicated by within-species variation. Many species are known as both winged and wingless forms (Wang et al., 2019, note that Australian species seem particularly prone to winglessness). Wingless forms often show reductions in the sclerotisation of the thorax. It is difficult to name a single feature of the genus that does not find exception in some species or other. Most species are weakly sculpted. For the most part, the maxillary stylets are short and sit low and far apart in the head when retracted. The mouth-cone is similarly short and rounded. The head is often fairly short with rounded cheeks that do not bear strong setae. Setae on the anterior margin of the pronotum are often reduced. The wings, if present, are often more or less constricted at about mid-length. Many phlaeothripids possess a series of large setae on the abdomen that hold the wings in place when folded back; in individuals of Psalidothrips with such setae (obviously, they tend to disappear in wingless individuals), they are often relatively few in number and simply curved.

Many of these features are related to the thrips' litter-dwelling habits. The short mouthparts, for instance, presumably reflect how these thrips are gleaning fungi from the surface of leaves without needing to pierce the leaf's cuticle. As such, it will be interesting to see how the genus holds out as our understanding of thrips phylogeny improves. Is this a true evolutionarily coherent assemblage, or disparate travellers who are following a fashion?

REFERENCE

Wang, J., L. A. Mound & D. J. Tree. 2019. Leaf-litter thrips of the genus Psalidothrips (Thysanoptera, Phlaeothripidae) from Australia, with fifteen new species. Zootaxa 4686 (1): 53–73.

In Honour of Amblyseius

At this point in time, the Phytoseiidae are one of the most intensely studied families of mites. They are the only group of mesostigmatan mites to have significantly diversified among the foliar environment (on and around plant leaves) where they are mostly predators on other small invertebrates. The taxonomic history of phytoseiids is storied and complex but one taxon that has been consistently recognised as a major part of the family is the genus Amblyseius.

Swirski mite Amblyseius swirskii, from here.


When reviewed by Chant & McMurtry in 2004, Amblyseius was a sizeable assemblage of close to 350 known species (I quite expect that number to have expanded by now). Species of Amblyseius are lightly sclerotised, mostly pale in colour, and usually have a smooth shield covering most of the dorsum. The genus is characterised by the presence of eighteen or nineteen pairs of setae on the dorsum of the idiosoma (the central body) with three sublateral pairs being particularly long: one about the level of the third pair of legs (referred to as the s4 pair) and the other two towards the rear of the body. Except for a few pairs forward of the s4 setae, the remaining dorsal setae are all minute.

The primary focus of human interest in phytoseiids has been their role as predators of crop pests. I described some of the ways in which phytoseiids have been commercially utilised in an earlier post. Species used in this way include several Amblyseius though matters are complicated slightly by changes in taxonomy (for instance, one species which has been widely traded as Amblyseius cucumeris is now placed in the genus Neoseiulus). One of the most widely used of the commercial phytoseiids in recent years has been Amblyseius swirskii, commonly known as the Swirski mite (E. Swirski being an acarologist after whom the species was named). This species was first described in 1962 from almond trees in Israel and subsequently identified from a wide range of plant and crop species. Its history in pest control has been described in detail by Calvo et al. (2015).

The Swirski mite feeds on a range of prey, including mite, thrips and whitefly species, as well as on pollen and micro-fungi. It was first promoted as a commercial control for silverleaf whitefly Bemisia tabaci in the early 2000s. However, it did not get taken up in a big way until media publicity about pesticide residues on capsicum crops in Spain led to a crash in demand. Farmers in that country were forced to look for alternative means of pest control and found great success with A. swirskii (previous attempts to use the cooler-clime preferring Neoseiulus cucumeris in Spain had not been promising). Since then, the Swirski mite has been adopted in numerous countries for use on a range of crops to control various pests such as western flower thrips Frankliniella occidentalis. Because of its ability to grow and thrive on non-insect foods, including artificial diets, this mite is easily cultured commercially. It may also be released on crops before pest infestations develop, building up numbers on a diet of pollen until suitable prey presents itself. For the same reason, Swirski mite populations do not crash before pest control is complete. Overall, a remarkable success and a prime example of the value of Amblyseius species to mankind.

REFERENCES

Calvo, F. J., M. Knapp, Y. M. van Houten, H. Hoogerbrugge & J. E. Belda. 2015. Amblyseius swirskii: what made this predatory mite such a successful biocontrol agent? Experimental and Applied Acarology 65: 419–433.

Chant, D. A., & J. A. McMurtry. 2004. A review of the subfamily Amblyseiinae Muma (Acari: Phytoseiidae): part III. The tribe Amblyseiini Wainstein, subtribe Amblyseiina n. subtribe. International Journal of Acarology 30 (3): 171–228.

By the Light of the Pony

Light-emitting organs have evolved in many different species of marine fish. For the greater part, they are associated with inhabitants of the deep sea, the twilight and midnight zones beyond the reach of celestial light. Light production by species found in shallow waters is much less common. Nevertheless, one particularly notable radiation of near-surface glowers is the ponyfishes of the family Leiognathidae.

Leiognathus equulus, copyright Sahat Ratmuangkhwang.


Ponyfishes are small, mostly silvery fishes found in coastal and brackish waters in tropical regions of the Indo-West Pacific. The largest ponyfishes grow to about 25 cm in length but most species are much smaller (Woodland et al. 2002). They live in large schools that forage near the surface at night, descending close to the bottom sediment during the day. Why these animals are referred to as 'ponyfishes', I have no idea (perhaps the head is meant to look a bit pony-like?) An alternative vernacular name of 'slipmouth' makes a lot more sense as these fish have highly extensible jaws that can be used to snipe prey out of the water. A groove along the top of the skull allows for reception of a long, mobile premaxilla, supporting the mouth as an elongate tube when extended. Most ponyfishes are planktivores with simple, minute teeth in the jaw and the mouth extending horizontally. Species of the genus Deveximentum have the mouth tilted obliquely at rest so that it stretches upwards when extended. Members of the genus Gazza are piscivores when mature, feeding on other fish, and possess a pair of large caniniform teeth in each of the upper and lower jaws to hold their prey (James 1975).

Ponyishes are also notable for their elaborate light-producing organs. In most bioluminescent fishes, the photophores sit on or close to the skin surface but in leiognathids it is an internal outgrowth of the gut. A cavity around the end of the oesophagus houses colonies of bioluminescent bacteria, usually the species Photobacterium leiognathi. This light organ sits alongside or projects into the gas bladder which has a reflective internal coating. In many species, patches of scale-less, translucent skin allow the transmitted light to shine forth brightly. Muscular 'shutters' associated with the light organ allow the fish to control light transmission more directly (Woodland et al. 2002).

Photopectoralis bindus, copyright D. G. R. Wiadnya.


In a review of ponyfish taxonomy by James (1975), no mention was made of the light-emitting organ or many of its associated structures (though reference was made to the absence of scales on certain parts of the body). With the exceptions of the distinctive genera Gazza and Deveximentum, ponyfishes were assigned to a broad genus Leiognathus. Since then, variations in the structure of the light organ have been recognised as taxonomically significant, allowing the recognition of several genera divided between two subfamilies Leiognathinae and Gazzinae (Chakrabarty et al. 2011). Leiognathinae is defined by plesiomorphic characters and is likely to be paraphyletic to Gazzinae (Sparks & Chakrabarty 2015).

Because of the nocturnal habits of ponyfish and the delicacy of the light-emitting structures, our understanding of how light production functions in Leiognathidae remains somewhat limited. In Leiognathinae and females of Gazzinae, the light organ is relatively small and the external body surface lacks translucent patches. For the most part, light is expressed in these individuals as a uniform ventral glow that probably functions as counter-illumination (the light from the venter prevents the fish from appearing as a silhouette against light from the water surface to predators swimming below). Alternatively, light may be flashed to warn school-mates of danger. In males of Gazzinae, conversely, the light organ is enlarged relative to females and associated with translucent 'windows'. The shape of the organ and the arrangement of the 'windows' is a primary factor in distinguishing genera. Rhythmic flashing of light has been observed in males of many gazzine species and is probably characteristic of the group as a whole. Woodland et al. (2002) observed a school of several hundred Eubleekeria splendens flashing their lights synchronously shortly after nightfall. The exact function of such displays is uncertain, whether in courtship displays, co-ordinating school movements, attracting prey or dissuading predators. The sexually dimorphic nature of the light organ system, together with its species-specific expression, might seem to favour the first of these options but it should be noted that they are not all mutually exclusive.

Despite their small size, ponyfishes are often significant food fish for people living in areas where they are found. Thanks to their schooling behaviour, they are often a major component of dredge catches. In the Philippines, they are used for making bagoong, a fermented fish paste. In other places, they may be cooked whole after cleaning. The glow, sadly, does not survive the process.

REFERENCES

Chakrabarty, P., M. P. Davis, W. L. Smith, R. Berquist, K. M. Gledhill, L. R. Frank & J. S. Sparks. 2011. Evolution of the light organ system in ponyfishes (Teleostei: Leiognathidae). Journal of Morphology 272: 704–721.

James, P. S. B. R. 1975. A systematic review of the fishes of the family Leiognathidae. J. Mar. Biol. Ass. India 17 (1): 138–172.

Sparks, J. S., & P. Chakrabarty. 2015. Description of a new genus of ponyfishes (Teleostei: Leiognathidae), with a review of the current generic-level composition of the family. Zootaxa 3947 (2): 181–190.

Woodland, D. J., A. S. Cabanban, V. M. Taylor & R. J. Taylor. 2002. A synchronized rhythmic flashing light display by schooling Leiognathus splendens (Leiognathidae: Perciformes). Marine and Freshwater Research 53: 159–162.

Centaurea acaulis, Stemless Star-thistle

In an earlier post, I commented on the diversity of species of the star-thistle genus Centaurea. Among the many, many species that have been assigned to this genus is the stemless star-thistle Centaurea acaulis* of northern Africa.

*Though dissolution of the polyphyletic Centaurea may lead to this species changing places. Banfi et al. (2005) listed it under the name of Colymbada acaulis.

Patch of stemless star-thistles Centaurea acaulis, from L'herbiel de Gabriel.


Centaurea acaulis is an inhabitant of dry, rocky habitats that is native to Tunisia and northeastern Algeria. As indicated by both the vernacular and botanical names, its growth habit lacks a central stem. Instead, the long, lobed leaves (which can be up to about a foot in length going by photos provided by Agut Escrig et al., 2021) lie prostrate on the ground. These leaves end in a large, ovate apical section with lobes running down the side of the central rib, becoming smaller towards the base. Flower heads are solitary and carry a mass of bright yellow florets. The involucral bracts (the 'scales' around the outside of the base of the flower head) are flat and green with darker longitudinal veins. The distal section of the bracts is triangular with a membranous, ciliate margin and typically (though not always) ends in a long spine. A closely related species found in northwestern Algeria and Morocco, C. oranensis, has historically been treated as a subspecies of C. acaulis (under the name C. acaulis ssp. boissieri, because botanical nomenclature is weird). However, C. oranensis was raised to species level by Greuter & Aghababian (in Greuter & von Raab-Straube, 2005) on the basis of its distinct involucral bracts, which are distally blackish, ovate and concave, with a margin of dense, long, stiff setae.

Close-up of flower head of Centaurea acaulis, copyright Stephen Mifsud.


Recent years have seen this species extending its range northwards with populations now found in Spain, Italy and Malta. In Malta, it was initially found grown in a disturbed area with particularly alkaline soil (Buttigieg & Lanfranco 2001). The mechanism of its arrival is uncertain. It could have dispersed naturally across the Mediterranean, or it may have arrived mixed into bird seed. However it got there, one might expect that as the south of Europe becomes increasingly hotter and drier, the stemless star-thistle will continue to spread.

REFERENCES

Agut Escrig, A., J. P. Solís Parejo & P. Urrutia Uriarte. 2021. Noticias sobre la presencia de Centaurea acaulis L. (Asteraceae) en la Península Ibérica. Flora Montiberica 81: 51–54.

Banfi, E., G. Galasso & A. Soldano. 2005. Notes on systematics and taxonomy for the Italian vascular flora. 1. Atti Soc. It. Sci. Nat. Museo Civ. Stor. Nat. Milano 146 (2): 219–244.

Buttigieg, R., & E. Lanfranco. 2001. New records for the Maltese flora: Centaurea acaulis L. (family: Asteraceae). Central Mediterranean Naturalist 3 (3): 147–148.

Greuter, W., & E. von Raab-Straube (eds) 2005. Euro+Med notulae, 1. Willdenowia 35: 223–239.

Lifestyles of the Rosalinidae

Among the modern foraminiferans, one of the most prominent radiations is among members of the Rotaliida, characterised by globose chambers and calcareous, hyaline test walls. Among the numerous families making up the Rotaliida are members of the Rosalinidae.

Benthic form of Rosalina globularis, from Brady (1884).


Rosalinids may be regarded as fairly typical-looking marine rotaliids with the test growing freely as a low trochospire (so a flattened cone or dish shape). The aperture of the test is a low slit on the interior margin along the umbilicus (Hansen & Revets 1992). Rosalinids have a complex life cycle involving both benthic and planktonic stages (Sliter 1965). The asexually reproducing diploid stage is benthic. Depending on conditions, diploid individuals may divide to produce other diploid individuals, resulting in several asexual generations. Eventually, however, the diploid generation will undergo meiosis to produce the haploid sexual generation (in the common species Rosalina globularis, this is induced by exposure to warmer water). In the sexual generation, a large globular chamber forms at maturity that covers the umbilical side of the test. This float chamber becomes filled with gas, allowing the foram to disperse planktonically before releasing gametes to produce the next diploid generation. Planktonic individuals are distinct enough in appearance from their benthic counterparts that they were long mistaken for distinct taxa before their identity was revealed by lab cultures.

Life cycle of Rosalina globularis, from Sliter (1965).


The majority of forams are particulate feeders. A network of filamentous pseudopodia radiating outwards from the cell body captures micro-organisms and other organic particles. However, one genus of rosalinids, Hyrrokkin, lives as parasites on sessile invertebrates (Cedhagen 1994). Species of this genus have variously been found on sponges, corals and bivalves. On sponges, they settle on the inhalent surface of the sponge and dissolve the underlying tissues. On bivalves, they form pits on the shell surface from which they bore holes through to the body cavity. Pseudopodia extended through this hole allow the foram to feed on host tissue. Infested hosts may bear multiple scars from the foram moving about on the outer surface. The forams may also feed on other animals such as polychaete worms or bryozoans attached to the surface of their primary host. In such cases, Hyrrokkin remains in its original pit but develops an irregularly shaped chamber with its aperture directed towards the alternate prey. Hyrrokkin species evidently do well from their rapacious lifestyle: whereas other rosalinids are only a fraction of a millimetre in diameter, Hyrrokkin sarcophaga is an absolute giant reaching around six millimetres across and with protoplasm containing thousands of nuclei. Proving once again that one may make a great deal of profit from the labour of others.

Cross-section of Hyrrokkin sarcophaga boring into shell of file clam Acesta excavata, from Schleinkofer et al. (2021).


REFERENCES

Cedhagen, T. 1994. Taxonomy and biology of Hyrrokkin sarcophaga gen. et sp. n., a parasitic foraminiferan (Rosalinidae). Sarsia 79: 65–82.

Hansen, H. J., & S. A. Revets. 1992. A revision and reclassification of the Discorbidae, Rosalinidae, and Rotaliidae. Journal of Foraminiferal Research 22 (2): 166–180.

Sliter, W. V. 1965. Laboratory experiments on the life cycle and ecologic controls of Rosalina globularis d'Orbigny. Journal of Protozoology 12 (2): 210–215.