Field of Science

The Trechodini


The above figure, from Uéno (1990), shows Trechodes satoi, a fairly typical representative of the carabid ground beetle tribe Trechodini. Members of this tribe are found in many parts of the world, though they are absent from the Nearctic region and were unknown from northern Asia prior to the description of Eotrechodes larisae from the Russian Far East by Uéno et al. (1995). The greatest diversity of Trechodini is on the southern continents and most authors have accordingly assumed a Gondwanan origin for the lineage.

The Trechodini are a subgroup of the subfamily Trechinae (in the restricted sense; sometimes this grouping is reduced to a tribe in which case Trechodina is treated as a subtribe thereof). Trechines are a distinctive group of relatively small ground beetles, features of which include a head with well-developed frontal furrows extending from the front of the head to behind the eye, and two pairs of supra-orbital setae. Trechodini differ from other trechines in distinctive male genitalia in which the ejaculatory duct of the aedeagus is entirely exposed dorsally, the median lobe is open above and gutter-like, and there is no basal bulb. They also usually have three obtuse teeth near the base of the mandible though the South African genus Plocamotrechus is missing one of these teeth in the left mandible (Moore 1972).

Habitus of Canarobius oromii, from Machado (1992).


Despite being widespread, the distribution of Trechodini is patchy. They are generally restricted to damp habitats such as alongside streams and rivers. Among Australian species, Moore (1972) noted that the genera Trechodes and Paratrechodes were uniformly fully flighted whereas Trechobembix and Cyphotrechodes were often brachypterous. He suggested that this was connected to the last two genera being found in more stable habitats alongside standing water. A number of species in the tribe have moved into subterranean habitats such as caves and have reduced wings and eyes. In two genera found in lava caves on the Canary Islands, Canarobius and Spelaeovulcania, no trace of the eyes remains (Machado 1992). Considering the little-studied nature of such habitats around the world, it is possible that other trechodins remain to be discovered.
REFERENCES

Machado, A. 1992. Monografía de los Carábidos de las Islas Canarias (Insecta, Coleoptera). Instituto de Estudios Canarios: La Laguna.

Moore, B. P. 1972. A revision of the Australian Trechinae (Coleoptera: Carabidae). Australian Journal of Zoology, Supplementary Series 18: 1–61.

Uéno, S. 1990. A new Trechodes (Coleoptera, Trechinae) from near the northwestern corner of Thailand. Elytra 18 (1): 31–34.

Uéno, S., G. S. Lafer & Y. N. Sundukov. 1995. Discovery of a new trechodine (Coleoptera, Trechinae) in the Russian Far East. Elytra 23 (1): 109–117.

Metavononoides: Retreating from the Coast

I've commented before on the taxonomic issues bedevilling the study of South American harvestmen, particularly members of the diverse family Cosmetidae. Recent years have seen researchers make gradual but steady progress towards untangling these multifarious snarls by more firmly establishing the identities of this family's many genera.

Metavononoides guttulosus photographed by P. H. Martins, from Kury & Medrano (2018).


The genus Metavononoides was established by Roewer in 1928 for two species from south-eastern Brazil. As with other Roewerian genera, its definition was not exactly robust, being based on a combination of tarsal segment count together with the presence of a pair of large spines on the dorsal scutum. The genus was later re-defined by Kury (2003) who used it for a group of species found in the Brazilian Atlantic Forest region around Rio de Janeiro. Members of this group shared a number of distinctive features including the presence of a distinctive U-shaped marking (later dubbed a 'lyre mask' or 'lyra')on the scutum. A number of species previously placed in other genera were transferred to Metavononoides, and the next few years saw the description of a couple more species in the genus. And then Paecilaema happened.

The genus Paecilaema was first established by C. L. Koch in 1839 but a poor description of its type species P. u-flavum lead to confusion about its identity. Over time, Paecilaema became associated with a large number of species over a range stretching from Mexico to Brazil (as an aside, it doesn't help matters that Paecilaema has been one of those names that taxonomists have found themselves chronically uncertain how to spell). When Kury & Medrano (2018) recently set out to determine the exact identity of Paecilaema by determining that of its type, they fixed P. u-flavum as a species that was common around Rio de Janeiro and that corresponded to one of the species included by Kury (2003) in Metavononoides. As a result, many of the species shifted by Kury (2003) into Metavononoides were shifted once again into Paecilaema. Many of the species assigned to Paecilaema from outside the Atlantic Forest Region remain unrevised but will almost certainly prove to require re-classification.

Metavononoides barbacenensis photographed by P. H. Martins, from Kury & Medrano (2018).


Metavononoides was not outright synonymised with Paecilaema, though. Among the group of species possessing the aforementioned lyra on the scutum, Kury & Medrano (2018) identified two distinct subgroups. In one, corresponding to Paecilaema, the lyra is made up of two components. Part of the lyra is composed of light coloration on the plane of the scutum itself while another part is raised granules. In some species, these granules are particularly concentrated along the margins of the lyra (you can see an example on this on Flickr, photographed by Mario Jorge Martins; though labelled Metavononoides, this individual is now identifiable as Paecilaema u-flavum). In the second subgroup, corresponding to Metavononoides, the differentiated coloration on the plane of the scutum is absent and the lyra is composed solely of raised granules. Not only are the two genera morphologically distinct, they are also more or less geographically distinct. Whereas Paecilaema is found in the moist broadleaf forests closer to the coast, Metavononoides is now restricted to species largely found in the grasslands and shrublands further inland, corresponding to the Cerrado region. Though more depauperate of species than it was before, the identity of Metavononoides is certainly firmer.

REFERENCES

Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1–337.

Kury, A. B., & M. Medrano. 2018. A whiter shade of pale: anchoring the name Paecilaema C. L. Koch, 1839 onto a neotype (Opiliones, Cosmetidae). Zootaxa 4521 (2): 191–219.

Roewer, C. F. 1928. Weitere Weberknechte II. II. Ergänzung der: "Weberknechte der Erde", 1923. Abhandlungen der Naturwissenschaftlichen Verein zu Bremen 26 (3): 527–632, 1 pl.

Strike up the Bandfish

The diversity of fishes can be absolutely overwhelming and, as a result, there a some distinctive groups that fail to get their time in the spotlight. For this post, I'm briefly highlighting one of the lesser-known fish families, the bandfishes of the Cepolidae.

Australian bandfish Cepola australis at home in its burrow, copyright Rudie H. Kuiter.


Cepolids are small fish (growing to about 40 cm at most with many species much smaller) that are widespread in the eastern Atlantic and the Indo-Pacific but nowhere common. They have a laterally compressed, tapering body and a lanceolate caudal (tail) fin. They have an angled mouth that is relatively large compared to their size and pelvic fins with a single spine and five segmented rays, four of which are branched (Smith-Vaniz 2001). Two subfamilies are recognised, the Cepolinae and Owstoniinae. The Cepolinae are particularly elongate in body form and have the dorsal and anal fins connected by membranes to the caudal fin; these three fins are all distinctly separate in the Owstoniinae. Cepolines are divided between two genera: Acanthocepola species have scaly cheeks and spines on the preopercular margin whereas Cepola have naked cheeks and no such spines. Classification of Owstoniinae has been a bit less settled. A recent revision of the subfamily recognised only a single genus Owstonia (Smith-Vaniz & Johnson 2016), synonymising the genus Sphenanthias previously distinguished by features of the lateral line. As an indication of how little-known cepolids are, Smith-Vaniz & Johnson's revision more than doubled the number of known species of owstoniine from fifteen to 36 .

Male Owstonia hawaiiensis, from Smith-Vaniz & Johnson (2016).


Cepolids are most commonly found in relatively deep water, up to about 475 m. They are not targeted by any significant fisheries though Wikipedia claims that the oldest known recipe from a named author is for the cooking of bandfish. Cepolinae live on sandy or muddy bottoms on continental shelves where they excavate burrows in which they insert themselves with the head protruding above the substrate. Owstonia species are free-swimming, more commonly found near rocky bottoms on upper slopes or around atolls. The diet, where known, appears to be composed of zooplankton though Smith-Vaniz & Johnson (2016) suggested on the basis of tooth morphology that Owstonia were detritivores for at least part of their life cycle.

REFERENCES

Smith-Vaniz, W. F. 2001. Cepolidae. Bandfishes. In: Carpenter, K. E., & V. H. Niem (eds) FAO Species Identification Guide for Fishery Purposes. The Living Marine Resources of the Western Central Pacific vol. 5. Bony fishes part 3 (Menidae to Pomacentridae) pp. 3331–3332. Food and Agriculture Organization of the United Nations: Rome.

Smith-Vaniz, W. F., & G. D. Johnson. 2016. Hidden diversity in deep-water bandfishes: review of Owstonia with descriptions of twenty-one new species (Teleostei: Cepolidae: Owstoniinae). Zootaxa 4187 (1): 1–103.

Goldenrod

Growing up as a child in rural New Zealand, I remember the community social events that would sometimes be held at the local district hall. On one evening, if I recall correctly, the event being held was a quiz night modelled after then-popular game show It's in the Bag. For those unfamiliar with this long-running institution, contestants on the show who successfully answered a series of general knowledge questions asked by Selwyn Toogood, a large avuncular man with an appropriately fruity voice, would be offered the choice between a cash prize up front or a 'bag' containing an unknown prize. This prize could potentially be something worth a lot more than the money on offer, such as a trip away or a home appliance (game shows in the 1980s often included whiteware among their top tier prizes). On the other hand, it could be worth a lot less, potentially even being effectively worthless (as viewers at home, of course, we always hoped for the latter). On this occasion, one of the 'prizes' on offer was a packet of seeds from 'the pretty yellow flowers that grow so vigorously in the region'. Everyone in the audience would instantly recognise the flowers in question as ragwort Senecio jacobaea, a pernicious weed much maligned due to its toxicity to livestock. Ragwort probably arrived in New Zealand as a contaminant in grass seed, but for today's post, I'm looking at another member of the daisy family which became a weed after being more deliberately spread around.

Tall goldenrod Solidago gigantea, copyright Pethan.


Solidago, the goldenrods, is a genus of perennial herbs with a woody caudex or rhizome and usually bright yellow flowers. About 100 to 120 species are currently recognised in the genus, the great majority of which are native to North America. Other species are found in South America and Eurasia, and a number of the North American species have been spread around the world by human activity. The number of species to be recognised is somewhat disputed because, as with many decent-sized plant genera, goldenrods have a tendency to laugh in the face in clear species concepts. Differences between species can be difficult to observe and hybrids are not uncommon. Individuals belonging to the same species may vary notably with geography and growth conditions and determining whether variation is genetic or environmental has historically required extensive growth experiments cultivating seed collections at varying locations. Vegetative spreading through rhizomes may lead to isolated populations of near-clonal individuals that may come to be recognised as 'microspecies'. As a result, what one author may recognise as a number of distinct species may be treated by another author as variants of a single species. For example, a study of altitudinal variants of the European S. virgaurea in Poland by Kiełtyk & Mirek (2014) lead them to recognise two species that had previously been confused, the lowland S. virgaurea and the montane S. minuta. The two were best distinguished by relatively fine-scale features of the flower heads, most notably the number of tubular florets in each head.

Canada goldenrod Solidago canadensis, copyright Olivier Pichard.


In a review of the North American Solidago species, Semple & Cook (2006) divided the genus between two sections. The smaller section Ptarmicoidei, including only half a dozen species, is characterised by clustering of flower heads in flat-topped arrays. The remaining species in the much larger section Solidago may have heads in rounded, conical or club-shaped arrays, or bear flower heads in axillary clusters. The distinctiveness of section Ptarmicoidei is enough that some authors have placed it as a separate genus Oligoneuron. Research is ongoing concerning the phylogeny of Solidago and its precise relationships with related genera.

Historically, the European Solidago virgaurea was valued for its supposed medicinal qualities (hence the genus name, which can be translated as 'becoming whole'). But while the dried flowers may still be used in making herbal tea, goldenrod does not seem to be currently regarded as of much pharmaceutical significance. As long ago as 1597, John Gerard noted in his Herball that the once highly prized herb had plummeted in value and regard once it was found to be growing wild in England, making it a mere local weed instead of an exotic import*. In the 1920s, Thomas Edison experimented with using goldenrod as a source of rubber. Investigations in this line were later continued in the 1940s by agrarian scientist George Washington Carver (under the patronage of Henry Ford), partially to counter rubber shortages during World War II. However, rubber yield from goldenrod is low and the rubber produced of low quality, so it never became a commercially significant source.

*'...in my remembrance, I haue known the dried herbe which came from beyond the ſea ſold in Bucklersbury in London for halfe a crowne an ounce. But ſince it was found in Hampſtead wood, euen as it were at our townes end, no man will giue halfe a crowne for an hundred weight of it: which plainely ſetteth forth our inconſtancie and ſudden mutabilitie, eſteeming no longer of any thing, how pretious ſoeuer it be, than whileſt it is ſtrange and rare. This verifieth our Engliſh proverbe, Far fetcht and deare bought is beſt for Ladies.'

Woundwort Solidago virgaurea var. leiocarpa, copyright Alpsdrake.


As alluded to above, a number of North American goldenrod species have been carried to temperate regions around the world as ornamentals or to provide nectar for bees. Unfortunately, some of these species have become significant invasive weeds in their adopted homes. Canada goldenrod Solidago canadensis can have an allelopathic effect on surrounding vegetation, producing water-soluble compounds that may inhibit the germination and growth of seeds (Werner et al. 1980). It may also act as a reservoir for pathogens of crop plants. Goldenrod is also commonly accused of causing hay fever but, in this regard at least, it seems to be largely innocent. Goldenrod plants shed relatively little pollen; as the flowers are insect-pollinated, the pollen is relatively unlikely to enter the air column. Instead, it seems that the conspicuous goldenrod flowers are blamed for the more copious pollen shed by less visible plants such as ragweeds flowering at the same time.

REFERENCES

Kiełtyk, P., & Z. Mirek. 2014. Taxonomy of the Solidago virgaurea group (Asteraceae) in Poland, with special reference to variability along an altitudinal gradient. Folia Geobotanica 49: 259–282.

Semple, J. C., & R. E. Cook. 2006. Solidago Linnaeus. In: Flora of North America Editorial Committee (eds) Flora of North America vol. 20. Asteraceae, part 2. Astereae and Senecioneae pp. 107–166. Oxford University Press: New York.

Werner, P. A., I. K. Bradbury & R. S. Gross. 1980. The biology of Canadian weeds. 45. Solidago canadensis L. Canadian Journal of Plant Science 60: 1393–1409.

Of Crosses and Clubs

One of the major groups of eukaryotes that has been somewhat under-represented on this site has been the Cercozoa. This is a diverse clade of unicellular organisms, distantly related to the foraminiferans and radiolarians, that has only been recognised within the last few decades with the introduction of molecular phylogenetic analyses. It has become increasingly clear that cercozoans form a major part of the world's microscopic biota but this diversity is poorly known as most cercozoans have little direct effect on human industry. One subgroup of the cercozoans that does make itself known in this regard, however, is the Phytomyxea.

Club roots of a rape plant infected by Plasmodiophora brassicae, photographed by Leafhopper65.


The Phytomyxea include parasites of plants, algae and other aquatic micro-organisms. The best known phytomyxean species, Plasmodiophora brassicae, causes a condition known as 'club root' in cabbages; another, Spongospora subterranea, is responsible for powdery scab on potatoes. They form multinucleate 'plasmodia' when growing within the cells of their host. Nuclei divide within the plasmodium in a characteristic cruciform pattern: the nucleolus does not break down during division but instead stretches elongately before pinching in two. While stretched, the nucleolus is oriented perpendicularly to the separating chromatin, forming a cross (Dylewski 1990). Owing to a superficial resemblance between phytomyxean plasmodia and those formed by the plasmodial slime moulds, phytomyxeans were historically also treated as slime moulds and hence as fungi (alternative historical names for the group, such as Plasmodiophoromycota or Plasmodiophoromycetes, reflect this supposed affinity). However, whereas the amoeboid plasmodia of slime moulds are capable of active movement and ingestion of food particles via phagocytosis, the phytomyxean plasmodium is more or less incapable of moving of its own volition, instead moving within the host cell by means of the host's own cytoplasmic streaming, and do not engulf host tissue in vacuoles. Slime moulds are no longer regarded as a single evolutionary lineage, and no 'slime moulds' are directly related to fungi.

Nuclei undergoing cruciform division in plasmodium of Tetramyxa parasitica, copyright James P. Braselton.


Over 40 species of Phytomyxea have been recognised to date but, not surprisingly, studies on the group have focused heavily on those species of economic importance to humans (Neuhauser et al. 2011). Terrestrial phytomyxeans produce thick-walled resting cysts, often aggregated in clumps known as cystosori, that may persist in soil for several years. These cysts hatch into biflagellate primary zoospores that seek out a suitable host. Upon finding one, the spore ceases swimming and adheres to the host cell before piercing the cell wall and injecting its cytoplasm which grows into the aforementioned plasmodium. Nuclei divide by mitosis and are eventually parcelled into sporangia that release secondary zoospores that escape from the host cell. These secondary spores generally do not disperse far; instead, they tend to cycle back and re-infect the original host to form new plasmodia. When these secondary plasmodia reach maturity, their nuclei divide meiotically and are divvied into new resting cysts. Presumably, the haploid nuclei produced in this manner fuse at some point with another to return to diploidy but it is unknown when exactly this happens. The cysts, when formed, each contain two nuclei but later only one, so it is possible that this reduction results from fusion. However, it might seem more likely that one of the nuclei breaks down without issue and the cyst remains haploid through to excystment with fusion occurring at the primary zoospore phase, thus allowing greater scope for cross-fertilisation. Marine phytomyxeans have long been thought not to produce resting cysts but recent observations of variations in zoospore morphology and sporangial wall thickness in the brown algal parasite Maullinia ectocarpii suggest the possibility of similarly complex life cycles (Neuhauser et al. 2011). The length of the phytomyxean life cycle can vary from about a month for Plasmodiophora brassicae to as little as one or two days for the brown algal parasite Phagomyxa algarum.

Diagram of the life cycle of Plasmodiophora brassicae, from Auer & Ludwig-Müller (2015).


For most phytomyxean species, infection by plasmodia causes physiological changes in the host, commonly taking the form of galls or other excesses of growth. Club root disease of Brassica results from Plasmodiophora brassicae plasmodia producing growth hormones that cause nutrients to be concentrated in the roots at the expense of leaf growth, thus increasing their availability to the parasite. Other alterations may be related to parasite dispersal. Ligniera junci, a parasite of rushes, causes a proliferation in the growth of root hairs in which the resting cysts form, providing an extra protective sheath. Plasmodiophora bicaudata is a parasite of marine Zostera eelgrass that produces galls at internodes together with reduced root growth. As a result, the eelgrass is easily uprooted by water movement, potentially being carried to new areas where the next generation of phytomyxeans can find new eelgrasses to infect.

REFERENCES

Dylewski, D. P. 1990. Phylum Plasmodiophoromycota. 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. 399–416. Jones & Bartlett Publishers: Boston.

Neuhauser, S., M. Kirchmair & F. H. Gleason. 2011. The ecological potentials of Phytomyxea ("plasmodiophorids") in aquatic food webs. Hydrobiologia 659: 23–35.

Ice-cream Cones of the Early Palaeozoic

It's time for something I haven't done in a very long time... (credit to Niel from Microecos):


I briefly described tentaculitoids on this site way back in September 2007. These narrowly conical shells of uncertain affinities were prominent members of the marine fauna during the Silurian and the Devonian, only to then disappear without a trace. No direct evidence is available for the soft-body appearance of the animals that produced them nor are we overly certain on their lifestyle. But at least one of the major subgroups of the tentaculitoids, the Dacryoconarida, are held to be of palaeontological significance due to their ubiquity and cosmopolitan distribution at the species level making them of use in biostratigraphy.

Reconstruction of Nowakia elegans, from Berkyová et al. (2007).


Dacryoconarids have generally been presumed to be planktonic in some way, owing to the aforementioned tendency of individual species to be found more or less worldwide, together with their small size (generally about the centimetre range). Dacryoconarids are distinguished from other tentaculitoids by the apical portion of their shell ending in a small globular bulb, presumed to represent the embryonic or larval shell of the original animal (Farsan 2005). A more or less distinct constriction or 'neck' separates this embryonic bulb from the remainder of the shell. In those forms with more heavily ornamented shells such as the genus Nowakia, a distinct juvenile section of the shell is visible immediately following the embryonic bulb in which the adult ornament is absent or weakly developed; said adult ornament, when it appears, takes the form of rounded transverse ridges and troughs, often associated with longitudinal and/or transverse striae. In other forms, such as the genus Styliolina, the outside of the shell is flat and ridgeless, with at most the only ornamentation present being striae. The inside of the shell may be rippled to follow the exterior ornamentation or it may be perfectly smooth (Fisher 1962).

Dacryoconarids are first recorded from the Late Ordovician but they remained at relatively low diversity until the Devonian which saw a notable radiation (Wittmer & Miller 2011). Nevertheless, they declined rapidly towards the end of the Devonian. It has been suggested that their extinction by the end of that period may be related to the appearance of more actively swimming predatory fish before which the tentaculitoids may have been relatively defenceless. Other early Palaeozoic planktic groups such as the graptoloids experienced a similar collapse at about this time, though the disappearance of the dacryoconarids may have lagged behind that of the graptoloids.

Styliolina clavulus, from Fisher (1962).


Over the years, a wide range of suggestions have been made about the affinities of the tentaculitoids, ranging from jellyfish to annelids. Perhaps the most persistent association has been made with molluscs but there really is little to support such a premise than the possession of a calcareous shell, a feature that is hardly unique to molluscs even among living animals. The structure of the tentaculitoid shell is most similar to that of some brachiopods (Fisher 1962) and some sort of brachiozoan affinity is perhaps the currently most favoured concept. As noted above, we know nothing about the tentaculitoid anatomy other than what we can infer from the nature of the shells themselves. In some larger tentaculitoids (though not among the dacryoconarids so far as we know) the apical parts of the shell may become walled off by solid septa so the living animal presumably didn't occupy the entire shell. Fisher (1962) described the tentaculitoids as "presumably tentacle-bearing" but I have no idea on what basis he made that statement (as I've noted before, the name 'tentaculitoid' itself comes not from a belief that they possess tentacles but from the mistaken interpretation of the first specimens named as being themselves the tentacles of larger animal). Tentacles would be a not unreasonable method of capturing the smaller micro-plankton on which the dacryoconarids presumably fed but it is not impossible that some other structure served this purpose.

REFERENCES

Farsan, N. M. 2005. Description of the early ontogenetic part of the tentaculitids, with implications for classification. Lethaia 38: 255–270.

Fisher, D. W. 1962. Small conoidal shells of uncertain affinities. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W98–W143. Geological Society of America, and University of Kansas Press.

Wittmer, J. M., & A. I. Miller. 2011. Dissecting the global diversity trajectory of an enigmatic group: the paleogeographic history of tentaculitoids. Palaeogeography, Palaeoclimatology, Palaeoecology 312: 54–65.