Different Modes Of Development Research Articles

The Molecular Basis of Differentiation Wave Activity in Embryogenesis

As development varies greatly across the tree of life, it may seem difficult to suggest a model that proposes a single mechanism for understanding collective cell behaviors and the coordination of tissue formation. Here we propose a mechanism called differentiation waves, which unify many disparate results involving developmental systems from across the tree of life. We demonstrate how a relatively simple model of differentiation proceeds not from function-related molecular mechanisms, but from so-called differentiation waves. A phenotypic model of differentiation waves is introduced, and its relation to molecular mechanisms is proposed. These waves contribute to a differentiation tree, which is an alternate way of viewing cell lineage and local action of the molecular factors. We construct a model of differentiation wave-related molecular mechanisms (genome, epigenome, and proteome) based on bioinformatic data from the nematode Caenorhabditis elegans. To validate this approach across different modes of development, we evaluate protein expression across different types of development by comparing Caenorhabditis elegans with several model organisms: fruit flies (Drosophila melanogaster), yeast (Saccharomyces cerevisiae), and mouse (Mus musculus). Inspired by gene regulatory networks, two Models of Interactive Contributions (fully-connected MICs and ordered MICs) are used to suggest potential genomic contributions to differentiation wave-related proteins. This, in turn, provides a framework for understanding differentiation and development.

Translocation precipitates natural hybridisation and pervasive introgression between marine gastropods with divergent developmental modes

Assisted colonisation, the introduction of species beyond their historical range, is increasingly necessary for conserving species. However, empirical evidence of the long-term genetic outcomes of assisted colonisation is grossly lacking. A risk associated with moving species beyond their native range is the possibility of interspecific hybridisation with a closely related species, potentially resulting in outbreeding depression or the genetic swamping of a parental species. Here, we use a combination of genome-wide Single Nucleotide Polymorphism (SNP) markers and mitochondrial DNA sequencing to determine the long-term genetic consequences of introducing the intertidal periwinkle Bembicium vittatum (a direct developer) beyond its native range and into the native range of its congener Bembicium auratum (a species with planktotrophic larval dispersal). We found novel evidence of natural, multigenerational hybridisation between marine invertebrates with different modes of development. Intriguingly, introgression was highly asymmetrical initially, but became more evenly bidirectional as the population became more admixed. There was a significant decline in the frequency of alleles from the introduced B. vittatum over time, providing evidence of genetic swamping. The present study also provides potential evidence of outbreeding depression, in the form of cytonuclear incompatibilities, leading to the observed pattern of asymmetrical introgression. This study reveals the potential for unexpected mixing between species when reproductive barriers are not well understood, resulting in failure of pure B. vittatum to persist at the translocation site, a major concern associated with assisted colonisation. Without long-term genetic monitoring interspecific hybridisation between B. vittatum and B. auratum would have gone undetected, highlighting the importance of long-term monitoring to detect unintentional negative consequences of conservation translocations. Successful assisted colonisation requires an understanding of the potential for interspecific hybridisation between the threatened species and closely related native species, to reduce the risk of adverse outcomes.

MODES OF ADHESIVE BONDING LAYER FORMATION DURING ROLL MOTION IN THE PROCESS OF SHEET LAMINATION

Novel technologies for the synthesis and processing of materials and products based on these materials, such as additive manufacturing, require the use of mathematical modeling to study the accompanying physical and chemical phenomena. These technologies include sheet lamination, which today has a variety of applications and numerous modifications. This article presents a model of adhesion layer formation in the creation of multilayer composites, which is controlled by a hot roller moving along the surface of the top layer. The dynamics of reagent heating depends on the thermal properties and sizes of all layers, the temperature of the roller, and its pressure against the surface, with characteristic times and spatial scales for different processes. The transition to dimensionless variables allowed the identification of dimensionless complexes to determine different modes of development of the adhesion layer synthesis process. Based on the combustion theory and non-equilibrium thermodynamics, new criteria of the process initiation and transition to a quasi-stationary mode were elaborated. The behavior of various thermodynamic quantities was analyzed in detail, including heat storage in the heated layer, enthalpy excess, and entropy production. The reaction zone is wide in most cases. The dependences of the half-conversion time on the model parameters are plotted for a finite layer size. This is a new characteristic for sheet lamination technology. A controlled mode, a fast bulk synthesis mode, a slow transformation mode maintained by the heat stored in the inert materials, and a quasi-stationary mode are identified. Criteria were established for different modes of reactions under conjugate heat exchange conditions.

Linear breakwater reefs of the greater Caribbean: Classification, distribution & morphology.

Geomorphic differences among Caribbean reefs have long been noted. These differences are considered to reflect the presence of reefs in different stages of development, following an incomplete recovery from rapid deglacial sea-level rise. But the possibility that these reflect real developmental differences caused by variation in wind, wave, and climate regime, has never been fully considered. Here, for the first time, we quantify the geomorphology and distribution of Greater Caribbean reefs using satellite images in Google Earth and public-domain bathymetry. To do this, we first standardise their classification based on shallow geomorphology, substrate depth, and physiographic setting, and then count and categorise the total number of reefs. These data show a total of 1023 linear breakwater reefs with a combined length of 2237 km. Of this total length, 80% are fringing reefs, 16% are barriers and 4% are faros and atolls. In terms of categories, there are 16 reef subtypes present, but only 9 are common. Their distribution, however, is not uniform. In particular, flat-subtypes form 60% of breakwater reefs in southern regions, but are less common in northern regions where crest-subtypes dominate (80%). To distinguish the geomorphology of these common reef subtypes, we collect size- and length-related morphometric data from their main reef zones. These data reveal that flat and crest subtypes also have morphometric differences: flat subtypes have well-constrained morphologies with statistically consistent unimodal morphometrics characterised by large back-reef zones, smaller and steeper reef fronts, and more sinuous and persistent crestlines. Crest subtypes, by contrast, have multimodal morphometrics suggesting less consistent morphologies (or unresolved subtypes), and are characterised by crestlines with lower sinuosity, more variable back-reef and reef-front areas, and slopes. These differences in geomorphology and distribution imply that flat- and crest-subtypes are neither successional stages of a single reef type, nor a genetically related sequence of types, but distinct reefal geoforms with different modes of development. In subsequent work we will explore what controls these differences.

Molecular and morphological description of a novel microsporidian Inodosporus fujiokai n. sp. infecting both salmonid fish and freshwater prawns.

A new microsporidian disease of cultured rainbow trout Oncorhynchus mykiss has recently been confirmed in Japan, and the causative species was tentatively designated as Microsporidium sp. RBT-2021. Involvement of common prawn Palaemon paucidens in its transmission was suggested based on the previous feeding trials, although the microsporidian infection in P. paucidens was not confirmed. In this study, P. paucidens in Lake Biwa, Japan was investigated for microsporidian infection and 4 types of spores (types 1-4) were newly found. The nucleotide sequence of the small subunit ribosomal RNA gene was identical between type 1 and Microsporidium sp. RBT-2021, indicating they are conspecific. However, intriguingly, the spore morphology and the mode of development in fish and prawn were strikingly different. Morphological observations revealed type 1 in the prawn possesses characteristics of the genus Inodosporus Overstreet and Weidner, 1974, while Microsporidium sp. RBT-2021 in the trout exhibited the characteristics of the genus Kabatana Lom, Dyková and Tonguthai, 2000. In the phylogeny, type 1 was placed within a clade comprising Kabatana spp. and Inodosporus octosporus. Based on the morphological and molecular analyses, we describe Microsporidium sp. RBT-2021 as Inodosporus fujiokai n. sp. Together with the success of the previous prawn-feeding trials, this study strongly suggests I. fujiokai n. sp. has a multi-host life cycle utilizing fish and crustacean hosts and different modes of development in each host. Such polymorphic life cycle has barely been known among fish microsporidians. This study also suggests that the genus Kabatana is a junior synonym of the genus Inodosporus.

Experimental Study of the Engineering Mechanical Properties of the Foundation Soil for Offshore Wind Power Platforms

Most of the coastal beach zone in the world is rich in wind energy reserves and has great potential for offshore wind power development. However, the sedimentary environment in the coastal area is complex and changeable, and the nature of the foundation soil of offshore wind power platforms is weak and complex, which is quite different from that in the land areas. In order to systematically study the mechanical properties of marine foundation soils, a series of geotechnical tests are carried out on representative undisturbed seabed soils, such as basic laboratory geotechnical tests, bender element tests, undrained triaxial shear tests, and resonance column tests. The test results show that shear wave velocity (Vs) of marine silt and silty clay increases linearly with the buried depth; the stress-strain relationship curves of silty clay and silt present two different modes of development: strain hardening and strain softening, the undrained shear strength (Sd) of the two types of marine soils decreases with the increase of the void ratio (e), and both present a good single correlation. Based on the relationship between Sd and Vs from the laboratory test of disturbed seabed soils, an undrained strength evaluation method of undisturbed seabed soils under the current stratum conditions incorporating in situ shear wave velocity is established. The dynamic shear modulus (G) in the various strain ranges of undisturbed silty clay and silt increases regularly with the buried depth (H). Meanwhile, the maximum dynamic shear modulus (Gmax) linearly increases with the increase of H, whereas the attenuation relationship of G decreases with the increase of H. The prediction method of G based on buried depth is established with high accuracy.

COVID-19 and Azerbaijan: Is the System Resilient Enough to Withstand the Perfect Storm?

ABSTRACT COVID-19 has significantly impacted many countries of post-Soviet Eurasia, affecting both political and economic realms. Azerbaijan is not alone in suffering from the pandemic and paying a high price. All the problems the country inherited are being exacerbated, forcing the government to seek different modes of development and the managing of governmental affairs. The following article will examine the possible impact of COVID-19 on the political and economic situation in Azerbaijan, and try to predict the future implications of the government’s actions for the system.

A comparison of the parameters of the chromatographic separation of the mixture of dyes obtained by caLC on the adsorbents type RP-8 and RP-18

The aim of the presented research was to compare the chromatographic separation process, a mixture of food dyes obtained in capillary action liquid chromatography (caLC) columns packed with adsorbent type RP-8 and RP-18 and using as the eluent: methanol-water-acetic acid (4:5:1, v/v). The obtained retention data were compared with separation in caLC columns with different internal diameters, different distance of migration and the different mode of development the chromatograms.

Allometric exponents as a tool to study the influence of climate on the trade-off between primary and secondary growth in major north-eastern American tree species.

Trees invest in both primary (e.g. height) and secondary (e.g. diameter) growth. The trade-off between these investments varies between species and changes with the tree growing environment. To better establish this trade-off, readily available allometric exponents relating height to diameter at breast height (γ(h,dbh)) and stem volume to diameter at breast height (α(v,dbh)) were simultaneously studied. Allometric exponents α(v,dbh) and γ(h,dbh) were obtained from 8893 individual tree stem analyses from two broadleaved species (Betula papyrifera, Populus tremuloides) and four conifers (Picea glauca, Picea mariana, Pinus banksiana, Abies balsamea) in the temperate and boreal forests of the province of Quebec, Canada. α(v,dbh) and γ(h,dbh) were related to tree age, stand density index (SDI), and mean temperature (TGS) and total precipitation (PGS) of the growing season. α(v,dbh) and γ(h,dbh) were found to be invariant with PGS and positively related to SDI and TGS for all species except Pinus banksiana. The parameter values associated with SDI and TGS were of higher value for conifers than for broadleaved species. This suggests that conifers and broadleaved species have different growth patterns. This could be explained by their different mode of development, the conifer species having a stronger apical dominance than broadleaved species. Such results could be further considered in allocation studies to quantify future carbon stocks in managed forests.

High Performance Thin Layer Chromatography Fingerprint Profile of Rhizome Extracts of Five Important Curcuma Species

The genus Curcuma (Family: Zingiberaceae) has 80 different species. Some of the species have been used world-wide as functional food and traditional medicines. The bright coloured pigments in the rhizome of different Curcuma sp. come mainly from fat soluble polyphenolic compounds known as curcuminoids. It comprises of three different pigments: curcumin, demethoxycurcumin and bisdemethoxycurcumin whose concentration varies from the species to species. A variety of spectrophotometric methods have been used for the quantification of the curcuminoids. However, quantification of the individual curcuminoids is not possible with spectro-photometric methods. Very little information is available on the determination of the individual constituents of curcuminoids using high performance thin layer chromatography. This method has advantages in terms of accuracy, flexibility, parallel analysis of a large number of samples and different modes of development. The present study was undertaken to provide information on the physico-chemical characteristics of individual curcuminoid pigments of five important Curcuma sp. to facilitate their proper extraction, separation and identification of individual phyto-constituents and their further utilization in the crop improvement programme.

Two Species of the GenusStrobiligera(Caenogastropoda: Triphoridae) with a Multispiral Protoconch in Southeastern Brazil

The genus Strobiligera Dall, 1924, sometimes treated as a synonym of Inella Bayle, 1879, included up to now species geographically restricted to the North Atlantic Ocean, usually occurring at great depths. The present study records the genus Strobiligera in the South Atlantic Ocean, with the recognition of two species in Southeastern Brazil. The shell of Strobiligera delicata sp. nov., which has a white teleoconch and a light brown protoconch, is very similar in general coloration to the shells of Strobiligera georgiana (Dall, 1927) comb. nov. and Strobiligera indigena (Dall, 1927) comb, nov., both from the southeastern coast of the United States. However, S. delicata differs from those species in shell shape, number of axial cords on the teleoconch and earlier development of the adapical spiral cord of the teleoconch. Strobiligera inaudita (Rolán and Lee, 2008) comb, nov., previously known from the southern coast of the United States, is diagnosed by a teleoconch with adapical and abapical spiral cords tinted with brown and white nodules, and by a completely white median spiral cord. Strobiligera delicata, S. inaudita, S. georgiana and S. indigena have multispiral protoconchs, similar to those of their congeneric species from the East Atlantic (Europe and North Africa) and Mediterranean. Other species of Strobiligera from the Caribbean and neighboring areas, including the type species Triforis ibex Dall, 1881, have a paucispiral protoconch. Hence, the generic allocation of species with a multispiral protoconch to Strobiligera cannot be considered definitive, and should be confirmed by subsequent anatomical studies of species with different modes of development.

Proefschriften 25 jaar na dato 37. Vatbaarheid voor parodontale aandoeningen

In the eighties of the former century it was observed that individuals had different modes of development of periodontitis, largely for unknown reasons. It was assumed that periodontal disease developed as a result of the presence of virulent micro-organisms in combination with an inadequate host response. The concept of this (im)balance in host parasite interactions developed further, in part because of new research techniques. With respect to oral bacteria it was shown that periodontal pathogens like Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Tannerella forsythia are risk factors for periodontitis. Furthermore, genetic polymorphisms (SNP's) have been shown to modulate the host response against the periopathogens. Medical and lifestyle factors, e.g. diabetes mellitus, smoking, psychological stress and, to a minor extent, also hormonal changes can have an impact on the progression of periodontitis. All this information contributes to determining the individual risk profile of a patient for developing periodontitis and for estimating the prognosis of periodontal treatment and maintenance care on an individual basis.

Reproductive biology of four ophiocomid ophiuroids in tropical and temperate Australia – reproductive cycle and oogenic strategies in species with different modes of development

The Ophiocomidae, a species-rich family of ophiuroid echinoderms, encompasses a range of developmental modes. We investigated the reproductive biology of four species: Ophiocoma dentata with planktotrophic development and a small egg, and three species with lecithotrophic development and eggs that differ in size (Clarkcoma pulchra, C. canaliculata and O. endeani). Reproduction was investigated by in situ observations, spawning trials and/or gonad histology. Gonad histology of O. dentata from the Northern and Southern Great Barrier Reef indicated that spawning occurs for six to seven months from January to June/July. Gonads of O. endeani, an endemic of subtropical New South Wales, were mature from December to February. In situ observations of two populations of C. pulchra and C. canaliculata in the Sydney region indicated they spawn from December to May. Egg morphology showed modifications in oogenesis associated with the evolution of a large egg, particularly in enhanced deposition of lipid. The eggs of O. dentata, a planktotrophic developer, contained densely packed, strong periodic acid Schiff's + yolk granules and were negatively buoyant. The eggs of species with lecithotrophic development were dominated by lipid droplets indicating that the evolutionary modification of oogenesis resulted in differences in yolk granule and lipid droplet distribution potentially influenced by selection for egg buoyancy.

Effects of Patch-Size on Populations of Intertidal Limpets, Siphonaria spp., in a Linear Landscape

Organisms with different life-histories and abilities to disperse often utilise habitat patches in different ways. We investigated the influence of the size of patches of rock (separated by stretches of sand) on the density of pulmonate limpets (Siphonaria spp.) along 1500 km of the linear landscape of the South African coastline. We compared the influence of patch-size on two congeneric species with different modes of development, S. serrata a direct developer, and S. concinna a planktonic developer. We tested the spatial and temporal consistency of the effects of patch-size by sampling 7 independent regions spanning the distributional range of both species of limpets, and by sampling one region at monthly intervals for 1 year. Within each region or month, 4 small patches (<20 m in length) interspersed with the 4 large patches (>60 m in length) were sampled. Across the entire geographic range and throughout the year, there were more of both species of limpets in large patches than in small patches. In most regions, there was greater variability in large patches than small patches. Variability within patches in a single region was similar throughout the year, with greater variability of both species in large than in small patches. We found little influence of the mode of development on the response of limpets to patch-size. Our findings highlight the importance of understanding patterns of distribution of species with respect to habitat heterogeneity in linear landscapes, and contradict the idea that organism mobility at an early ontogenetic stage directly affects habitat use.

The Collaborative Recordist

Collaboration within the recording studio has moved through different modes of development since the early 1900s. This process represents the development of the recordist from entrepreneur to collaborative artist. In this article I explore the progress of the collaborative role between the studio recordist and theartist. By examining the recording processes of new ‘retro-sonic’ rock music, I document an example of the contemporary roles of studio recordists, and explore modes of both traditional and more sophisticated recording methods and evolving processes of collaboration.

Coe Genes Are Expressed in Differentiating Neurons in the Central Nervous System of Protostomes

Genes of the coe (collier/olfactory/early B-cell factor) family encode Helix-Loop-Helix transcription factors that are widely conserved in metazoans and involved in many developmental processes, neurogenesis in particular. Whereas their functions during vertebrate neural tube formation have been well documented, very little is known about their expression and role during central nervous system (CNS) development in protostomes. Here we characterized the CNS expression of coe genes in the insect Drosophila melanogaster and the polychaete annelid Platynereis dumerilii, which belong to different subgroups of protostomes and show strikingly different modes of development. In the Drosophila ventral nerve cord, we found that the Collier-expressing cells form a subpopulation of interneurons with diverse molecular identities and neurotransmitter phenotypes. We also demonstrate that collier is required for the proper differentiation of some interneurons belonging to the Eve-Lateral cluster. In Platynereis dumerilii, we cloned a single coe gene, Pdu-coe, and found that it is exclusively expressed in post mitotic neural cells. Using an original technique of in silico 3D registration, we show that Pdu-coe is co-expressed with many different neuronal markers and therefore that, like in Drosophila, its expression defines a heterogeneous population of neurons with diverse molecular identities. Our detailed characterization and comparison of coe gene expression in the CNS of two distantly-related protostomes suggest conserved roles of coe genes in neuronal differentiation in this clade. As similar roles have also been observed in vertebrates, this function was probably already established in the last common ancestor of all bilaterians.

I Do I Undo I Redo: The Textual Genesis of Modernist Selves in Hopkins, Yeats, Conrad, Forster, Joyce, and Woolf (review)

Reviewed by: I Do I Undo I Redo: The Textual Genesis of Modernist Selves in Hopkins, Yeats, Conrad, Forster, Joyce, and Woolf Edmund Lloyd Epstein (bio) I Do I Undo I Redo: The Textual Genesis of Modernist Selves in Hopkins, Yeats, Conrad, Forster, Joyce, and Woolf, by Finn Fordham. Oxford: Oxford University Press, 2010. 281 pp. £55.00. The latest work of Finn Fordham, an astute genetic critic of modern literature, deals with the relationship between the personality of the author and its development during the creation of his work. The title of the book, I Do I Undo I Redo, refers to the processes of self-definition before, during, and after this imaginative process. The authors treated—Gerard Manley Hopkins, W. B. Yeats, Joseph Conrad, E. M. Forster, James Joyce, and Virginia Woolf—present different personalities and different modes of development in the genesis of their most characteristic writings. Here, Fordham shows himself again to be a sensitive critic of literature and presents many valid insights into the works of these authors. He does not, however, proffer an effective definition of human personality, and the analogical processes in the creation of the works are sometimes not really relevant to the virtues of the works themselves. For example, in a chapter on Hopkins, Fordham analyzes "The Windhover" as an example of the "compression of sound" and finds a relationship between Hopkins's "compression" and his difficulty [End Page 313] in achieving an audience for his works (95).1 It is certainly true that Hopkins does not employ simple syntax, yet "compression" is not the most felicitous way of describing the poet's treatment of language. He is not, after all, Robert Browning, for whom syntactic compression was a feature of general style but not of an individual poem. Hopkins constantly tried to convey the essence of the objects and creatures in his poetry-their "instress"—by relevant linguistic structures in the poems themselves (109).2 In his treatment of some of the other writers, Conrad in particular, Fordham misses an important point of criticism. He notices, with great sensitivity, the emotional difficulties with which Conrad was wrestling in his writing of Heart of Darkness, including a monstrous writer's block deriving from his dreadful experiences in the Congo. Fordham should note, though, that Conrad derives benefits from his struggles with composition. In Marlow, the narrator of Heart of Darkness, Conrad creates for the first time a typically modern figure: the shattered narrator.3 Marlow has been so deeply shocked by his experiences in Central Africa that he cannot tell the story of what happened to him in any consecutive way. There are gaps filled with suffering that the reader must fill. This is an innovation in literature. If we compare the method of narration of Heart of Darkness with that of, say, Charles Dickens's Great Expectations, we see immediately the novelty of Conrad's approach. Pip, the narrator of Great Expectations, has suffered a catastrophic alteration of attitude by the end of the book, a radical change of belief about all of his life. His prosperity is not due to Miss Havisham, as he thought, or to any rotting, wealthy source but rather to the convict Magwich, whom he had helped as a boy. This change of belief would be the equivalent of an emotional earthquake in any normal life, but we have no evidence of this from Pip's narration of the story. If Conrad had written Great Expectations, Pip's narration would have consisted of a series of shattered dazzling fragments resembling Marlow's narration of Heart of Darkness. Therefore, Fordham's point—that Conrad's writer's block derived only from his African experience and contributed to the narrative form of Heart of Darkness—could have been expanded into a general commentary on the nature of first-person as narration as changed by Conrad. This is, in general, the pattern of the book: Fordham's brilliant historical analyses of the lives of the writers he discusses and their relation to elements in the works themselves suffer from a lack of generalization and require expansion into other areas where they can elucidate larger critical areas of literature...

Varied development of trunk segmentation in three related Upper Devonian phacopine trilobites

In many arthropods, the development of the trunk region is a complex part of post-embryonic development. Consideration of fossil ontogeny provides an additional source of data and a broader evolutionary perspective on the evolution of arthropod body patterning. Here, I examine the development of the thoraco-pygidial exoskeleton of three related phacopine trilobites from the Upper Devonian according to the integrated ontogenetic scheme proposed by Hughes et al. Pygidial shields assigned to three ontogenetic series gave us the opportunity to further explore the evolutionary pattern of the trilobite segmentation. The analysis showed a different mode of development in two of three species and thus reveals variability between the related taxa. Comparison of the boundaries of different aspects of ontogenesis ratifies the diversity of the segmentation process among trilobites and even among related phacopine species. Results include (i) in a synarthromeric trunk condition recorded to date, there has consistently been a preceding ‘equilibrium’ phase for the late meraspid pygidium and (ii) two developmental modes, i.e. both hypoprotomeric development and synarthromeric development, occur contemporaneously in closely related taxa. Such developments suggest that aspects of segmental development such as segment accretion and segment articulation were able to vary in a labile manner.

Generic demarcation of Permo-Triassic Claraia-like species and their biogeographic significance

Three types of byssal notch are present in Permo-Triassic Claraia-like species, i.e. Claraia-type, Pseudoclaraia-type and Claraioides-type. At present, there is no consensus in the use of the generic names. The preferred classification should be both useful in practice and compatible with the rules of taxonomy. For the genera in question, details of the byssal notch are important in assessing relationships because the morphology of this structure may closely reflect phylogenetic affinities. However, a particular feature of the notch may have great significance in one taxon but low significance in a related taxon. In order to seek the best taxonomic characters for classification of Permo-Triassic Claraia-like species, we should follow empirical evidence rather than preconceived opinions. Pseudoclaraia Zhang, 1980 should be considered a junior synonym of Claraia Bittner, 1901 because the Pseudoclaraia-type and Claraia-type byssal notches form a continuum within populations. In contrast, all known Claraioides species possess the Claraioides-type byssal notch, which is their synapomorphy, indicating monophyly. The notch is characterized by ventral enlargement due to ventral dissolution and by its contracted anterodorsal outlet due to the accretion of shell material. This is a unique character in Palaeozoic bivalves. It implies that the Claraioides byssal notch must have had a different mode of development than the other two types of byssal notch. It is thus unreasonable to place Claraioides in synonymy with Claraia. A review of the biogeographic patterns of Permo-Triassic Claraia-like species indicates that trans-oceanic dispersal of Claraia from the Boreal Realm to the rest of the world may have occurred during the latest Permian. It is possible that volcanic-winter effects triggered the trans-oceanic dispersal and the tremendous change in Permian–Triassic global biogeographical patterns.

Cloverleaf Skulls

Cloverleaf skulls (Kleeblattschädel-Syndromen, trilobular skulls) have different modes of development (pathogenetic variability). Synostosis may involve various sutures in different types of cloverleaf skulls. Their facial features, radiographic findings, and CNS anomalies are also reviewed. Different causes of cloverleaf skulls have been identified (etiologic heterogeneity). One table lists 26 different conditions with trilobular skulls identified under various etiologic headings: monogenic, chromosomal, disruptive, iatrogenic, and distinctive conditions of unknown cause. Discussed in detail are type 2 thanatophoric dysplasia, type 2 Pfeiffer syndrome, Apert syndrome, amniotic bands, Say-Poznanski syndrome, and COH syndrome. Another table summarizes the relative frequencies of the cloverleaf skull syndromes.