Ant-lions of Australia

Austrogymnocnemia edwardsi, photographed by Shaun Winterton.
For today's post, I'll be looking at a group of lacewings known as the Periclystina. Earlier posts on lacewings have looked at members of the families Chrysopidae, Kalligrammatidae and Hemerobiidae; the Periclystina belong to a further family, the Myrmeleontidae. Myrmeleontids are commonly known as ant-lions (indeed, Myrmeleon is derived from the Greek words for 'ant' and 'lion'), particularly their larvae which are fat-bodied animals with large mandibles and flip-top heads. Ant-lion larvae dig themselves into soft ground at the bottom of a conical pit; when crawling insects such as ants walk over the edge of the pit, they end up sliding down to the bottom of the cone and into the waiting jaws of the ant-lion. Ant-lions can dig themselves into the ground quite quickly; this video from Wikipedia shows an ant-lion attempting to capture prey and digging itself into the ground.

Ceratoleon brevicornis, photographed by Shaun Winterton (again).
For all their charms, larval ant-lions could not be described as elegant animals. The adults, though, are as attractive as any lacewing, which is very attractive indeed. The Periclystina are a subtribe recognised by Stange (1976) within the tribe Dendroleontini of the subfamily Myrmeleontinae, and were distinguished by Stange from other dendroleontins primarily by features of the female genitalia (such as the absence of anterior gonapophyses). Stange included seven genera in the Periclystina, all of them endemic to Australia (one genus, Periclystus, has since also been found in New Guinea—New 1990). The Australian Dendroleontini were revised by New (1985), who pointed out that some of the features used by Stange (1976) to distinguish his subtribes were not entirely reliable. Though New did not formally dismantle Stange's system, it is telling that he did not make any attempt to place his own new genera within it, and Stange's subtribes may require further examination.

Angular-wing lacewing Periclystus circuiter, from Brisbane Insects.
Many Periclystina are large and eye-catchingly patterned. The species of Periclystus are particularly remarkable with oddly scalloped ends to their wings. The irregular wing shape together with their patchy markings function to camouflage the insect when it sits along a twig. Also remarkable is Ceratoleon brevicornis, with antennae much shorter than those of any other ant-lion. Other than that, I think the pictures I'm sharing with you here largely speak for themselves.

Glenoleon falsus, photographed by Donald Hobern.
REFERENCES

New, T. R. 1985. A revision of the Australian Myrmeleontidae (Insecta: Neuroptera). II. Dendroleontini. Australian Journal of Zoology, Supplementary Series 105: 1-170.

New, T. R. 1990. Myrmeleontidae (Insecta: Neuroptera) from New Guinea. Invertebrate Taxonomy 4: 1-20.

Stange, L. A. 1976. Classificacion y catalogo mundial de la tribu Dendroleontini con la redescripcion del genero Voltor Navas (Neuroptera: Myrmeleontidae). Acta Zoologica Lilloana 31: 261-322.

The Stoneflies: Old or New?

Little snowfly Capnia nana, from here.

Despite being a working entomologist, I have to confess that there are some insect groups with which I am not entirely familiar. The stoneflies, Plecoptera, are one of those groups. I work in arid northern Australia, but stoneflies are associated with cool waters. The highest diversity live in temperate regions of the world; those whose ranges extend into lower latitudes are found higher in the mountains, away from the heat.

Stoneflies live in their favoured waterways as nymphs, emerging when they develop to adulthood (at least one species, Capnia lacustra of Lake Tahoe, appears to also be aquatic as an adult). The adults are large, long-bodied insects that are often better runners than they are fliers. Nymphs are primarily detritivores, but many species are carnivorous to a greater or lesser extent. Adults of some species do not feed; others feed on such things as encrusting algae or lichen or rotten wood. Depending on species, adult stoneflies may have full-sized wings, reduced wings or no wings at all; in some species, both flying and flightless morphs may be present. Two European species, Perla bipunctata and Perlodes microcephala, are solely brachypterous in Britain but may be either brachypterous or macropterous elsewhere in their range (Hynes 1976). Winged females of many species lay eggs while in flight, either dropping them into water or gliding to the water surface and letting the eggs be washed off from the end of the abdomen. Other species attach their eggs to stones underwater or insert them into crevices or rotting wood.

Tasmanian stonefly, Eusthenia sp., photographed by Nuytsia@Tas. More colourful than most other stoneflies, Eusthenia species raise their forewings when threatened to reveal brightly patterned hindwings.

Most recent authors have supported a division of the stoneflies between two lineages, the Antarctoperlaria and Arctoperlaria, that are both morphologically and geographically distinct (Zwick 2000). The Antarctoperlaria are found in South America, Australia and New Zealand. The Arctoperlaria, in contrast, are primarily found in the Northern Hemisphere (except for members of two families, the Perlidae and Notonemouridae). Many species of the Arctoperlaria signal to potential mates by drumming the abdomen on a substrate, a behaviour unknown in the Antarctoperlaria.

Nymph of Acroneuria abnormis, photographed by Michel Gauvin.

Stoneflies have often been regarded as one of the most primitive groups of winged insects, and their position remains contentious. The two main theories are that they are the sister group to all other neopteran insects (insects that are capable of folding the wings back flat over the body), or that they belong to the group known as Polyneoptera that also includes grasshoppers and cockroaches. Which of these is correct has been regarded as potentially significant in understanding how flight evolved in insects as a whole. As discussed in an earlier post, it has been suggested that insect wings are homologous with articulated gills in aquatic nymphs. As well as Plecoptera, the two living non-neopteran insect orders Odonata (dragonflies) and Ephemeroptera (mayflies) are aquatic as nymphs, and if Plecoptera are basal to other neopterans then it suggests that this life history may be ancestral for winged insects as a whole. However, differences in nymphal morphology between the three groups may indicate that the aquatic lifestyle has been independently acquired in all three from terrestrial ancestors, which would also be more likely if stoneflies are derived polyneopterans. Molecular studies have supported a polyneopteran relationship for stoneflies, but not with rock-solid support (e.g. Terry & Whiting 2005); morphological studies are equivocal and do not clearly point either way (Zwick 2009). The fossil record is also unclear: while a number of early insect groups have been connected to stoneflies, whether they are true stem-Plecoptera or closer to other polyneopteran lineages is debatable (Béthoux et al. 2011). It is also worth pointing out that while similarities between stonefly and mayfly gills have been cited in relation to their supposed homology with wings, different families of stoneflies have different gill types, and we still do not know whether and what kind of gills were ancestral for Plecoptera. Also, in those stoneflies with plate-like gills, the gills are not articulated like wings and incapable of independent movement (Zwick 2009).

REFERENCES

Béthoux, O., Y. Cui, B. Kondratieff, B. Stark & D. Ren. 2011. At last, a Pennsylvanian stem-stonefly (Plecoptera) discovered. BMC Evolutionary Biology 11: 248.

Hynes, H. B. N. 1976. Biology of Plecoptera. Annual Review of Entomology 21: 135-153.

Terry, M.D., & M. F. Whiting. 2005. Mantophasmatodea and phylogeny of the lower neopterous insects. Cladistics 21: 240–257.

Zwick, P. 2000. Phylogenetic system and zoogeography of the Plecoptera. Annual Review of Entomology 45: 709-746.

Zwick, P. 2009. The Plecoptera–who are they? The problematic placement of stoneflies in the phylogenetic system of insects. Aquatic Insects 31 (suppl. 1): 181-194.

The Pygmephoroidea: Lives of Phoresy and Fungi

Slide-mounted specimen of pygmephorid, Siteroptes sp., photographed by Qing Hai Fan.

Today's subjects, the Pygmephoroidea, are an assemblage of mites that are mostly free-living feeders on fungi, though exceptions occur. The taxonomic coverage of Pygmephoroidea does vary a bit between systems: Walter et al. (2009) divide the taxa covered in this post between two superfamilies Pygmephoroidea and Scutacaroidea, but Khaustov & Ermilov (2011) combine them all in the one superfamily. Taxonomy of the pygmephoroids is further complicated by presence in many species of distinct adult female forms, some of which were different enough to have been placed by past authors into different families. The normal adult female is a fairly sedentary individual, but other females are what are referred to as 'phoretomorphs', specialised to be able to disperse by hitching a ride on other animals (most commonly larger arthropods), a process known as 'phoresy'. Phoretomorphs tend to be more heavily sclerotised than the normal females, and may also differ in features such as fusion of the tibia and tarsus of the first pair of legs, and enlargement of the claws on the second and third pairs. For the most part, phoretic mites are only passengers of their hosts, and do not cause them any noticeable harm. However, some pygmephoroids in the family Microdispidae have become parasites.


Video of the life cycle of the pygmephorid Pediculaster mesembrinae.

Like ants and wasps, pygmephoroids have what is called a haplodiploid system of sex determination where unfertilised eggs hatch into haploid males and fertilised eggs into diploid females (Camerik et al. 2006). Only larvae and adult females feed; adult males live only to mate. In between the active larval and adult stages of the pygmephoroid life cycle is a quiescent nymphal stage (comparable to the pupal stage in insect development). Adult males of the family Scutacaridae will pick up a quiescent female nymph and carry her until she moults to adulthood and is ready for mating. After mating, normal females of Pygmephoridae and Microdispidae become physogastric: the hind part of their body swells up to relatively enormous size as their eggs develop within them; females of the pygmephorid Siteroptes ceralium may produce up to 500 offspring each (Scutacaridae swell slightly, but not to the extent of the other two families; phoretic females do not generally become physogastric until after they've left their dispersal host). In the microdispid genera Glyphidomastax and Perperipes, that feed on the larvae or eggs of the army ants they live with, the elongate physogastric body may mimic a young ant larva (Walter et al. 2009). In at least some species of Pygmephoridae, the progeny of a female will develop through the larval stage while still within the mother, and emerge at or close to maturity (a process that often involves the mother literally bursting open; even if it doesn't, pygmephoroid females do not survive long past egg-laying). As previously discussed in the related mite Acarophenax, males and females may even copulate while still inside their mother. In the pygmephorid Xenaster longiabdominalis, copulation occurs outside the mother, but the fully developed males are already grabbing their unmated sisters and carrying them away at the time of birth (Walter et al. 2009).

SEM of the scutacarid Imparipes, by Ernst Ebermann. In species of this family, one of the dorsal shields has become extended forward to cover the front of the body.

Some pygmephoroids such as the microdispid Microdispus lambi and the pygmephorid Pediculaster flechtmanni can cause damage to commercial mushroom crops. Other species are vectors of plant diseases, such as Siteroptes cerealium spreading carnation bud rot. The phoretomorphs of many pygmephorids possess structures on their underside to carry spores of their preferred food fungus with them as they travel; in a number of cases, the fungus in question happens to be a plant pathogen.

REFERENCES

Camerik, A. M., E. de Lillo & C. Lalkhan. 2006. The neotype of Pediculaster mesembrinae (Canestrini, 1881) (Acari: Siteroptidae) and the description of all life stages. International Journal of Acarology 32 (1): 45-67.

Khaustov, A. A., & S. G. Ermilov. 2011. A new species of the genus Siteroptes (Acari, Heterostigmata, Pygmephoridae) from European Russia. Zoologicheskii Zhurnal 90 (6): 756-760 (transl. Entomological Review 91 (4): 528-532.

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

The Rotaliida: Building a Wall

Tests of Elphidium crispum, photographed by Spike Walker.

The foraminifers have been featured on this site a number of times before, when various members of this diverse group of unicellular organisms have been introduced. Today, I thought I'd take a look at the broader classification of forams through the lens of one of their major subgroups, the rotaliidans.

The earliest classifications of forams divided them on the basis of the number and arrangement of chambers within the test, but over time the composition of the test walls came to be also recognised as an important feature (Haynes 1990). This reached an apotheosis of sorts in the Treatise on Invertebrate Paleontology classification of Loeblich and Tappan (1964), in which the forams were divided between five suborders primarily on the basis of test composition. These were the Allogromiina (with membranous or chitinous tests), Textulariina (with agglutinated tests) and three suborders with calcareous tests but differing wall structures: the microgranular Fusulinina, the porcelaneous, imperforate Miliolina and the hyaline, perforate Rotaliina (other authors would treat these groups as orders, with the suffix -ida instead of -ina). However, later authors (including Loeblich and Tappan themselves) regarded this classification as somewhat oversimplified, and divided groups such as the planktonic rather than benthic Globigerinida, the aragonitic rather than calcitic Robertinida, the Lagenida with monolamellar rather than bilamellar walls, and the high-spired or serial rather than planispiral Buliminida from the Rotaliida proper (Haynes 1990). However, many of the subdivisions within forams remained somewhat artificial, and potentially did not reflect true evolutionary relationships.

Bulimina marginata, photographed by Fabrizio Frontalini.

Molecular phylogenetics of forams got off to a fairly rocky start. For various reasons, extraction of reliably genetic samples from forams is a difficult process (for instance, their tendency to live in symbiotic associations makes contamination a continuing issue). However, studies have progressed to the point where a broad outline is beginning to emerge. One significant agreement between studies has been the monophyly of forams with a perforate calcareous test (Flakowski et al. 2005; Schweizer et al. 2008). The 'Globigerinida' and 'Buliminida' have both been shown to fall within this clade, and should probably not be distinguished from the Rotaliida. No representatives of the Lagenida or Robertinida appear to have been analysed molecularly; the lagenidans may be an independent lineage, while the robertinidans may be closely related to the Rotaliida (Sen Gupta 2002).

Suggested relationships of major foraminiferan groups from Sen Gupta (2002). This arrangement, which is somewhat concordant with available molecular data, proposes two separate lineages of multi-chambered forams, with calcareous members in each.

Within the Rotaliida, the most extensive molecular analysis has been that of Schweizer et al. (2008), whose results support a division between three main clades. Though reasonably well supported molecularly, these clades do not correspond to morphological divisions: the 'Buliminida', for instance, are divided between at least two clades. The planktonic forms may also be polyphyletic within the Rotaliida, though analyses have been inconsistent on their exact position in the clade (and Schweizer et al. do not include any globigerinidans in their analysis). Not all molecular results clash with the morphology, though: the Nummulitidae, a group of giant discus-shaped forams that get up to five centimetres in diameter, are one of a number of families that remain supported by either data source.

Internal chambers of Nummulites gizehensis, from the Natural History Museum. This species is most famous for being the major component of the limestone used in the construction of the pyramids of Giza.

REFERENCES

Flakowski, J., I. Bolivar, J. Fahrni & J. Pawlowski. 2005. Actin phylogeny of Foraminifera. Journal of Foraminiferal Research 35 (2): 93-102.

Haynes, J. R. 1990. The classification of the Foraminifera—a review of historical and philosophical perspectives. Palaeontology 33 (3): 503-528.

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

Schweizer, M., J. Pawlowski, T. J. Kouwenhoven, J. Guiard & B. van der Zwaan. 2008. Molecular phylogeny of Rotaliida (Foraminifera) based on complete small subunit rDNA sequences. Marine Micropaleontology 66: 233-246.

Sen Gupta, B. K. 2002. Modern Foraminifera. Springer.

From Giant Reeds to Tiny Leaves

Giant reed Arundo donax, photographed by Russ Kleinman & Richard Felger.

The grasses are without a doubt one of the most successful groups of plants in the modern environment. So it is only fitting that for today's post I'm going to be looking at one of the subgroups of the grasses, the Arundinoideae.

The Arundinoideae, including the reeds and related species, has been long recognised as a subfamily of grasses, but rather vaguely so. Most of the characters of leaf anatomy previously used to define the group are either plesiomorphies or absences. Arundinoids use the plesiomorphic C₃ photosynthetic pathway rather than the derived C₄ pathway and lack the radiate leaf anatomy associated with C₄ photosynthesis. They also lack the fusoid leaf cells with accessory arm cells that are characteristic of the bamboos. In other features, 'arundinoids' were quite variable, and it therefore came as no surprise to anyone when phylogenetic analyses indicated that the group was polyphyletic. As a result, the Grass Phylogeny Working Group (2001) divided the arundinoids between a number of subfamilies, separating the wiregrasses as the Aristidoideae and the oatgrasses and pampas grasses as the Danthonioideae. This reduced the Arundinoideae proper, previously including well over 600 species, to less than 40.

Common reed Phragmites australis, from here.

Even so, the arundinoids remain a disparate group, and morphological synapomorphies of the group remain elusive. The taxonomic core of the group, the reeds of the genera Arundo, Phragmites and Molinia, are connected by the possession of hollow culm internodes, a punctiform hilum (the detachment scar on the 'seed') and convex adaxial rib sides in the leaf blade (Grass Phylogeny Working Group 2001), but these features are not shared by all other arundinoids. The reeds are found in damp habitats, and the common reed Phragmites australis can grow in standing water. The largest species, the giant reed Arundo donax, can reach a height of ten metres under ideal growth conditions. In contrast, the Tom Thumb grass Dregeochloa pumila is found in the Namib Desert of South Africa and Namibia, and doesn't reach any higher than 25 mm (excluding the flower stalk, which may give it another inch or so). Dregechloa pumila is also remarkable as the only succulent species of grass. Also included in the Arundinoideae are the crinipoid grasses, a somewhat poorly known assemblage of species found in highlands of Africa, Madagascar and southern India (Linder et al. 1997).

Tom Thumb grass Dregechloa pumila, from Ernst van Jaarsveld.

Arundo donax has become known in some areas as an agressive weed, particularly in the US. It has one of the fastest growth rates of any plant, potentially up to ten centimetres in a single day (remember, that's four Dregeochloas!) Despite its invasive potential, some have been promoting it as a potential crop species, particularly for the biofuel market (presenting its fast growth rate as an outright advantage). Arundo donax is also the preferred material for woodwind reeds. Phragmites australis (also a problematic weed in the wrong circumstances) has been used in wastewater purification, and Wikipedia also notes that it is edible, quoting that the young stems "while still green and fleshy, can be dried and pounded into a fine powder, which when moistened is roasted like marshmallows". 'Like' marshmallows, perhaps, but I don't think that I'll be rushing to make the substitution.

REFERENCES

Grass Phylogeny Working Group. 2001. Phylogeny and subfamilial classification of the grasses (Poaceae). Annals of the Missouri Botanical Garden 88 (3): 373-457.

Linder, H. P., G. A. Verboom & N. P. Barker. 1997. Phylogeny and evolution in the Crinipes group of grasses (Arundinoideae: Poaceae). Kew Bulletin 52 (1): 91-110.

Birds of the Sun

Handsome sunbird Aethopyga bella, photographed by Tonee Despojo. This species was only recently separated at species level from the lovely sunbird Aethopyga shelleyi; one of the distinguishing features of the two is the purple ear-patch in A. bella.

The sunbirds are definitely forerunners in the tally of the world's most brilliantly coloured birds. This family of long-billed nectar-feeders, found in tropical regions of the Old World, is often compared to the New World hummingbirds. Like hummingbirds, the males of most sunbirds shimmer with brilliant iridescent colours (the exceptions are the spiderhunters of the genus Arachnothera); the females are much more restrained, generally shades of olive-green or brown. However, though hummingbirds are committed aerialists (as befits their relationship with the swifts and nightjars), sunbirds are, as Passeriformes, more likely to feed while perched on a stem alongside their chosen flower. Also, while sunbirds are primarily nectar feeders, they also feed to a fair extent on small insects (this is also true of hummingbirds).

Male (above) and female (below) of fork-tailed sunbird Aethopyga christinae. Male photographed by Frankie Chu, female by Neil Fifer.

Sunbirds are also a rather less diverse group than hummingbirds, both in number of species and in external appearance. Because of their structural similarity, authors have differed in the number of genera recognised in the family, but one group that has generally been differentiated is the Aethopyga sunbirds of southern Asia. Aethopyga species tend to be smaller than other sunbirds, with relatively short but strongly downcurved bills. The male has the central tail-feathers elongate (Ali & Ripley 1999). Aethopyga species are also distinguished from other sunbirds by the structure of the tongue. As with other sunbirds, the tongue is elongate, with the sides curved inwards to form a double tube. Differing from others, the end of the tongue is divided into two inwardly open tubes but with a basal bifurcated plate connecting the tubes:

Tongues of sunbirds of different genera showing differences in morphology, from Cheke & Mann (2001).

Cheke & Mann (2001) listed seventeen species of Aethopyga, with an eighteenth species being added by Mann (2002). Several of these species are also currently recognised as polytypic, with multiple subspecies. Though Mann's (2002) 'new' species was simply derived from the elevation of previously-recognised subspecies, one entirely new species of Aethopyga, A. linaraborae from Mindanao in the Phillippines, was only described as recently as 1997. No large scale analysis of the interrelationships between Aethopyga species appears to have been published as yet, but centres of diversity are the Philippines and the Himalayas.

Elegant sunbird Aethopyga duyvenbodei, photographed by Marc Thibault. Having been informed by their vernacular names that Aethopyga sunbirds are, in turn, handsome, lovely and elegant, it is all the sadder to say that this last species from Sangihe, near Sulawesi, is regarded as endangered.

REFERENCES

Ali, S., & S. D. Ripley. 1999. Handbook of the Birds of India and Pakistan, together with those of Bangladesh, Nepal, Sikkim, Bhutan and Sri Lanka, 2nd ed., vol. 10. Flowerpeckers to Buntings. Oxford University Press.

Cheke, R. A., & C. F. Mann. 2001. Sunbirds: A Guide to the Sunbirds, Flowerpeckers, Spiderhunters and Sugarbirds of the World. A & C Black Publishers.

Mann, C. F. 2002. Systematic notes on Asian birds. 28. Taxonomic comments on some south and south-east Asian members of the family Nectariniidae. Zool. Verh. Leiden 340: 179-189.

Linguipolygnathus Redux

Upper (left in each case) and lower (right, do.) views of representative Pa elements of polygnathids from Bardashev et al. (2000): (upper left) 'Linguipolygnathus' anastasiae; (upper right) 'Eolinguipolygnathus' nothoperbonus; (lower) 'Costapolygnathus' inversus. Bardashev et al. (2002) classify L. anastasiae closer to C. inversus despite regarding it as phylogenetically closer to E. nothoperbonus.

There are some things that you find yourself returning to like an itching scab. Yes, it's time for me to once again wade into the unsettling world of polygnathid conodont taxonomy.

Previous comments on the subject can be found here and here. To briefly recap: Bardashev et al. (2002) divided the Devonian conodonts of the Polygnathidae, most of them previously assigned to a single genus Polygnathus, between a number of families and genera. However, they explicitly represented a number of both families and genera as extensively polyphyletic. Later, Weddige (2005) responded to criticisms of the divided taxonomy by claiming that it represented a form taxonomy only. In my first post on the subject, I expressed confusion at what exactly Weddige meant by that claim.

On closer examination, I'm somewhat more inclined to take Weddige's claim at face value. Despite proposing detailed phylogenetic relationships between the species studied, Bardashev et al.'s (2002) taxonomy is supposed to prioritise identification above all. The primary division, Polygnathidae vs 'Eopolygnathidae', is based on a single character: the development of the basal cavity on the underside of the Pa element of the polygnathid apparatus. Presence of a basal cavity is the ancestral condition; within the 'eopolygnathids', the margins of the basal cavity become progressively closed in a number of lineages until, in the 'polygnathids', there is only a small basal pit remaining. So, for instance, the genera Eolinguipolygnathus and Linguipolygnathus are placed in separate families, despite the facts that (a) they differ in no other characters (the diagnoses provided for the two genera by Bardashev et al. are effectively identical), (b) 'Linguipolygnathus' is proposed to have arisen no less than five separate times from 'Eolinguipolygnathus' ancestors (and is not directly connected phylogenetically to other genera in its own family), and (c) relative to the other polygnathids examined, the two 'genera' supposedly share a clear and (more significantly) phylogenetically coherent character in the formation of the posterior part of the Pa element into a transversely ridged tongue.

Bardashev et al. argued that this division was necessary because the restricted basal cavity was the original character used to establish the Polygnathidae, so the inclusion of taxa with an open basal cavity violated the original diagnosis of the family. The possibility of revising the family diagnosis is not raised, despite their own research apparently showing that it does not diagnose a coherent group. The underlying motivation for this prioritisation of diagnostic characters over phylogeny seems to be the use of conodonts as markers in biostratigraphy. For instance, the type of Eolinguipolygnathus, Polygnathus dehiscens, has been proposed as the marker for the beginning of the section of the Devonian known as the Emsian. But does this emphasis on diagnostic features truly serve even biostratigraphy? Carls et al. (2008), for instance, claim that emphasis on characters of the ventral side of the conodont Pa element has lead to a number of distinct taxa being confused under the name 'Polygnathus dehiscens', leading to misdiagnosis of the Emsian boundary.

Just as I have stated before that a key should not be a taxonomy, a taxonomy should not be a key. Both are important, but both have their own roles to play.

REFERENCES

Bardashev, I. A., K. Weddige & W. Ziegler. 2002. The phylomorphogenesis of some Early Devonian platform conodonts. Senckenbergiana Lethaea 82 (2): 375-451.

Carls, P., L. Slavík & J. I. Valenzuela-Ríos. 2008. Comments on the GSSP for the basal Emsian stage boundary: the need for its redefinition. Bulletin of Geosciences 83 (4): 383–390.

Weddige, K. 2005. Contra Ruth Mawson’s critizising Bardashev, Weddige & Ziegler 2002, e.g. in SDS Newsletters 20 (2004). Subcommission on Devonian Stratigraphy Newsletter 21: 51-52.