Chancelloriid sclerites from the lowermost Cambrian of North China and discussion of sclerite taxonomy

Chancelloriid sclerites from the lowermost Cambrian Xinji Formation (Series 2, Stage 3), southern margin of the North China platform, are systematically described. Thousands of isolated sclerites from three sections are assigned to three genera and four species, including Chancelloria cf. eros, Allonnia tripodophora, Archiasterella pentactina, and Ar. tetraspina. To accurately document the taxonomic significance of the sclerite structure, modified formulas (m+nC, m+nA, and m+0) are put forward to represent the full series and variation of sclerite forms. Based on the sclerite construction, statistical analysis on the proportions of different sclerite forms in the rock samples and the composition of sclerites in previously described chancelloriid scleritomes, a new scheme for identification and classification of isolated sclerites reconciled within the framework of the complete scleritome, is proposed.     

Formation and morphology of epidermal sclerites from a deep-sea hydrothermal vent solenogaster (Helicoradomenia sp., Solenogastres, Mollusca)

The deep-sea hydrothermal vent solenogaster Helicoradomenia is covered with calcium carbonate sclerites. Light and electron microscopy reveal varying morphologies of these sclerites. Many sclerites have hollow tips and/or are pitted and etched. Bacteria are found on and in sclerites. Initial sclerite formation occurs in an extracellular crystalline chamber formed by the invagination of a cuboidal basal cell of the columnar microvillus mantle epithelium. As the sclerite grows, it fills the crystalline chamber resulting in direct contact with the microvilli of both the basal cell and neighboring secondary sclerite-forming cells. These cells shape a collar around the base of the growing sclerite. As growth continues, the sclerite-forming cells stretch around the sclerite forming a sheath in which the base of the sclerite resides. Mature sclerites grow through the cuticle into the external environment. The erosion pattern of sclerites reveals a less stable inner medullary region and a harder outer cortical region. This points to a secondary character state, where foremost hollow acicular sclerites develop into solid sclerites. This is in agreement with the systematic position of the genus Helicoradomenia within Simrothiellidae, a taxon typically with hollow sclerites.     

Sclerite-bearing alveolitid favositids from the Devonian of central Poland

Calcitic and pyritic pseudomorphs of originally siliceous monaxonic sclerites (predominantly heloclone-like monocrepid desmas) have been found entrapped within calcareous skeletons of alveolitid favositids identified as Squameoalveolites fornicatus (SchlÜter 1889) derived from Lower and Middle Devonian (Emsian and Eifelian) deposits of central Poland. The sclerites are arranged in a system of subvertical tracts forming a loose palisade along the midwall of skeletal tubes. Poorly preserved remnants of such palisades correspond to the so-called »median line« or »median suture« of typical favositids. The finding supports the hypothesis of poriferan affinity of favositid Tabulata and indicates that these common Palaeozoic fossils cannot be longer classified as Cnidaria. They should, on the basis of the sclerites, be regarded as remnants of monaxial and/or sublithistid demosponges, which - like the members of modern and fossil demosponges called sclerosponges or coralline sponges - had the ability to produce a basally secreted calcareous skeleton in addition to siliceous sclerites.     

SKELETAL MICROSTRUCTURE INDICATES CHANCELLORIIDS AND HALKIERIIDS ARE CLOSELY RELATED

Abstract: Chancelloriids are problematic, sac‐like animals whose sclerites are common in Cambrian fossil assemblages. They look like sponges, but were united with the slug‐like halkieriids in the group Coeloscleritophora Bengtson and Missarzhevsky, 1981 based on a unique mode of sclerite construction. Because their body plans are so different, this proposal has never been well accepted, but detailed study of their sclerite microstructure presented here provides additional support for this grouping. Both taxa possess walls composed of a thin, probably organic, sheet overlying a single layer of aragonite fibres orientated parallel to the long axis of the sclerite. In all halkieriids and in the chancelloriid genus Archiasterella Sdzuy, 1969 , bundles of these fibres form inclined projections on the upper surface of the sclerite giving it a scaly appearance. On the lower surface of the sclerite, the projections are absent. This microstructure appears to be unique to chancelloriids, halkieriids, and their relatives, siphogonuchitids and sachitids. (The sclerites of another putative halkieriid relative, Wiwaxia Walcott, 1911 , are unmineralized, making direct comparisons impossible.) Thus, similarity both at the level of sclerite construction and the level of sclerite microstructure suggests that chancelloriid, halkieriid, sachitid, and siphogonuchitid sclerites are homologous. The difference in chancelloriid and halkieriid body plans can be resolved in two ways. Chancelloriids either represent a derived condition exhibiting complete loss of bilaterian characters or they represent the ancestral condition from which the bilaterally symmetric halkieriids, and the Bilateria as a whole, derived. The latter interpretation, proposed by Bengtson (2005) , implies that coeloscleritophoran sclerites (‘coelosclerites’) are a plesiomorphy of the Bilateria, lost or transformed in descendent lineages. Given that mineralized coelosclerites appear in the fossil record no earlier than c. 542 Ma, this in turn implies either that the Ediacaran record of bilaterians has been misinterpreted or that coelosclerite preservability increased at the beginning of the Cambrian Period. The former is difficult to reconcile with Ediacaran trace and body fossil evidence, but the latter may be possible, reflecting either independent mineralization of organic‐walled sclerites in chancelloriids and halkieriids or the opening of a taphonomic window that favours coelosclerite preservation.     

Morphology,taxonomic position,and stratigraphic distribution of the early Cambrian skeletal problematics <Emphasis Type="Italic">Mobergella radiolata</Emphasis> Bengtson, 1968

Morphology of the phosphatic sclerites of the species Mobergella radiolata that come from the Lower Cambrian sections is studied, and the stratigraphic distribution of the species is revised. The sclerite laminated microstructure of this species is described and is shown to be similar to that of some gastropods, bivalves, brachiopods, bryozoans, and corals. The species M. hexactina Skovsted, 2003 and M. sibirica Skovsted, 2003 are shown to be junior synonyms of M. radiolata based on sclerite morphology supported by the results of statistical analysis.     

Morphology of the elytral base sclerites

The elytral base sclerites (= sclerites located at the articular region between the forewing and thorax in Coleoptera) of selected taxa were examined and homologized. Although the elytral base sclerites are highly modified compared to the wing base sclerites of the other neopterans, they can be homologized by using the conservative wing flapping and folding lines as landmarks. A reduction of the first axillary sclerite was identified as a general trend of the elytral base sclerites, although the sclerite usually has a very important function to mediate flight power from the notum to the wing. This result indicates that the functional constraint against the basal sclerites is relaxed because of the lack of an ability to produce flight power by elytra. In contrast, the elytral folding system formed by the basal sclerites is well retained, which probably occurs because proper wing folding is a key for the shelter function of the elytra. The elytral base sclerites apparently contain more homoplasies than the serially homologous hindwing base sclerites of Coleoptera, which suggests that the structure is less useful for higher-level systematics. However, the faster evolutionary rate of the elytral base sclerites suggests there is potential for studying the lower-level phylogeny of Coleoptera.     

Homology of the genital sclerites of Megaloptera (Insecta: Neuropterida) and their phylogenetic relevance

The genitalia of Megaloptera are crucial for taxonomic identification and represent a significant component of characters for phylogenetic interpretation of this order. However, several complex genital structures, especially those related to segments 9 and 11 in Megaloptera, have yet to be subjected to a comprehensive survey of homology. The terminology for genital sclerites has been variously and even incorrectly used by different authors, a fact which could lead to much confusion about character evolution. In this paper, we first present a comprehensive morphological comparison of the sclerites of male and female genital segments in 23 megalopteran genera representing all major lineages of Corydalinae, Chauliodinae and Sialidae. Accordingly, we then provide new interpretations on the homology of the genital sclerites which often appear to be considerably different among Megaloptera. Based on our new and revised homology assessments, we conclude that: (i) the small to medium‐sized sclerite beneath the ectoprocts in males of Sialidae represents the fused gonocoxites 11; (ii) the male gonocoxites 11 in Corydalidae are largely reduced and are sometimes retained as a small sclerite beneath the anus; (iii) the predominant sternite‐like sclerite of the female abdominal segment 8 represents the fused gonocoxites 8; and (iv) a pair of sclerites amalgamated with the lateral arms of male gonocoxites 10 in Chauliodinae is the gonocoxites 9. Furthermore, based on our genital homology assessments, we reconstruct an intergeneric phylogeny including all genera of Megaloptera using genital characters in a parsimonious analysis to test their phylogenetic relevance. The phylogeny herein recovered is largely congruent with the results from several previous studies, thus underlying the significant phylogenetic relevance of the megalopteran genital sclerites. The present work provides new insights into the evolution of insect genitalia.     

寒武纪叶足动物链状心网虫躯干骨板功能形态学研究*

链状心网虫(Cardiodictyon catenulum)是寒武纪澄江生物群中较为常见的叶足动物, 其躯干骨板的形态一直存在较大争议。本项研究显示该叶足动物的躯干具有一纵列马鞍状骨板, 每个体节具有单一的骨板, 每个骨板从背部延伸至躯干两侧。因此该叶足动物的骨板与其余具有成对或环状分布的躯干骨板的叶足动物存在显著的区别。骨板中央存在一个圆锥形凸起, 骨板边缘显著增厚且呈锯齿状。链状心网虫的躯干骨板边缘增厚和鞍点的凸起提升了整体的刚性; 锯齿状边缘也指示了更优的保护及防御功能。本项研究还发现链状心网虫骨板表面具有显微筛状结构, 筛孔被充填并保存为众多等距离分布的黄铁矿化瘤突, 与微网虫、怪诞虫及爪网虫躯干骨板的显微网状结构类似, 可能为纤细乳突的出口。本文认为: 寒武纪叶足动物的躯干骨板普遍具有显微筛状结构; 这些骨板除了保护与防御, 可能还有感觉的功能。每个躯干体节对应骨板为寒武纪叶足动物的独有衍征, 可能为背骨板的早期形态, 也可能由成对骨板愈合而来。     

Intra-specific variation in the morphology and the benefit of large genital sclerites of males in the adzuki bean beetle (Callosobruchus chinensis)

Rapid evolution has led to a large diversity in the sizes and morphology of male genitals across taxa, but the mechanisms driving this evolution remain controversial. In this study, we investigated the function of male genital sclerites in the adzuki bean beetle (Callosobruchus chinensis) and compared the length and morphology of genital sclerites between two populations that vary in their degree of polyandry. We found that the length of male genital sclerites was negatively correlated with copulation duration but positively correlated with the speed of matings with multiple females. Additionally, we found that the average length and number of genital sclerite spines of males from the more polyandrous population were larger than those from the less polyandrous population. We suggest that the genital sclerite of male adzuki bean beetles evolved by sexual selection, and a larger genital sclerite has a selective advantage because it allows for rapid copulations with multiple females.     

Der Neodarwinismus als axiomatisierbares deduktives System und das Problem der Anpassung und Selektion

In the last decade numerous evolutionary models have been proposed and intensively discussed. Surprisingly, the logical analysis of these different hypotheses is not of great importance in this debate. As a matter of fact, Neodarwinism is a consistent deductive system which is based on few but wellconfirmed axioms. Hence, very often, precise statements and definitions of standpoint can be made. This is exemplified by some repeatedly discussed models concerning the problems of Darwinian »adaptation« and »natural selection« 1. Following the logic of the Neodarwinian theory, extinction can only be the result of overspecialization if some very unusual assumptions are made. 2. The hypothesis of »punctuated equilibrium« GOULD 1982), the »effect hypothesis« (VRBA 1983) and the stochastic evolutionary model SCHOPF 1979) include elements which are logically inconsistent with the »modern synthesis«; they could be »true« only if at least one of the neodarwinian axioms (so far not disproved) is negated.     

Comparative morphology of the postmentum of bees (Hymenoptera: Apoidea) with special remarks on the evolution of the lorum

A comparative morphological study of the basal sclerites of the bee labium was undertaken. The term postmentum was applied to the basal sclerite of the bee labium. In contrast to recent interpretations, the undivided postmentum was found to be ancestral for bees and homologous with the single postmental sclerite of other Hymenoptera. This sclerite has previously been incorrectly indentified as two separate sclerites, usually termed mentum and lorum (= submentum), for many short-tongued bees (Colletidae, Halictidae, Andrenidae, Melittidae) and for the long-tongued families of bees (Anthophoridae, Fideliidae Megachilidae) excepting most members of the Apidae. The postmentum, divided into a true mentum and lorum, was found only in certain members of the Apidae. A phylogenetic implication resulting from this study shows that the Andrenidae may be the sister group to the MCL-T group (Melittidae, Ctenoplectridae and long-tongued families of bees). In addition, it is proposed that the Euglossinae should be the sister group to the Apinae (Meliponini, Apini and Bombini). This means that eusociality may be considered a synapomorphy for the Apinae.     

The dual role of sclerites in a gorgonian coral: Conflicting functions of support and defence

Sclerites in the gorgonian coral Briareum asbestinum perform the dual role of skeletal support against wave action and structural defence against predators. Local populations of B. asbestinum vary along gradients of decreasing water movement and decreasing predator abundance with increasing depth, such that sclerite length increases and sclerite density decreases with depth. Based on this pattern, I explored a possible trade-off between the sclerite composition that is most resistant to tearing versus most deterrent to predatory gastropods. Feeding assays revealed that artificial foods containing longer sclerites and those containing higher volume fractions of sclerites are less palatable to the gastropod Cyphoma gibbosum. However, real colonies appear constrained, in that they do not contain both long sclerites and high volume fractions at the same time. Given a choice among real colonies, snails prefer shallow-water colonies with shorter sclerites e ven though the sclerite volume fractions are high. Although least deterrent to snails, shallow-water colonies are 56% more resistant to tearing than their deep-water counterparts. Hence, variation in sclerite composition among local populations of B. asbestinum may be maintained by opposing selection for support versus defense.     

我国西南地区早寒武世小壳化石Sinosachites

采自四川峨嵋和云南会泽的磷酸盐化的Sinosachites骨片显示出中央沟和侧沟结构,并区别出三种不同类型的骨片(palmate,cultrate and siculate)。这一发现证实,产于澳大利亚的Thambetolepis(Jell,1981)是Sinosachites的晚出同义名。基于上述结构,该产地一些原定为Sachites和Halkieria的标本亦应归入Sinosachites。在Sinosachites属中确认出两个种,即产于华南的Sinosachites flabelliformis He和产于澳大利亚的Sinosachites delicatus(Jell)。在前一种中,左右型对称骨片的存在证实该动物两侧对称。骨片的基部通常保存为磷质内核,表明它比骨片壁更容易磷酸盐化,在组织学上它与骨片壁不同。骨片的基部可能原为有机质或部分矿化。在Sinosachites中,无帽状和束状骨片可能表明在coeloscleritophorans中halkieriids是一个介于wiwaxids和siphogonuchitids之间的类群。     

Scleritome construction,biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome.     

Pyritized preservation of chancelloriids from the Cambrian Stage 3 of South China and implications for biomineralization

The enigmatic Cambrian animal chancelloriids were discovered in a wide range of taphonomic settings; however, preservation of biomineralized sclerite microstructure was solely known from secondarily phosphatized skeletal remains. Here, we investigate a uniquely pyritized chancelloriid from the lower Cambrian Guojiaba Formation in southern Shaanxi Province, China, using a combination of advanced analytic techniques. Results of the energy dispersive spectroscopy (EDS), X-Ray Fluorescence (XRF), and Raman spectrum show that the sclerites and scleritomes are preserved as pyritized internal moulds with a calcitic outer layer. The outer layer enveloping the internal moulds likely represents the recrystallized counterpart of the original biomineralized sclerite wall. Distinctive fibrous microstructures are discovered in the sclerites, which echo the features seen in the phosphatized fossils of chancelloriids. The typical microstructure, along with the recrystallized calcite, corroborate the interpretation that chancelloriid sclerites were originally constructed by fibrous aragonite. The stability of the microstructure and mineral composition in both carbonate and siliciclastic backgrounds indicate that chancelloriids were adapted to exploit aragonitic fibres to build their skeletons regardless of the change of their living environments.     

Variations in the arbitrariness of ASL: an assessment of the symbolicity of simian signs

This paper summarizes and applies a continuum of «arbitrariness» or «symbolicity» composed of symptoms, rituals and symbols to the results of research in which American Sign Language (ASL) was used as the method of «language» training. Additionally, an expansion of the symbolicity continuum to include a continuum of «abstractness» with the «conceptual symbol» anchoring the most arbitrary end of the continuum was advanced. The results of the comparison provide additional support for the claim that apes are capable of learning and using symbolic signs. However, only a small number of those symbolic signs could be considered «conceptual symbols».     

Sclerite calcification and reef-building in the fleshy octocoral genus Sinularia (Octocorallia: Alcyonacea)

Alcyonacean octocorals in tropical reefs are usually not considered as reef builders. Some Sinularia species, however, are capable of consolidating sclerites at the colony base to form spiculite. Nanwan Bay, southern Taiwan, features both fossilized and recently formed boulders composed of spiculite, thus demonstrating the role of Sinularia in contributing to the reef structure. Section radiography of an 18.5 kg spiculite boulder demonstrated a regular density banding of 3–6-mm intervals. Core survey indicated spiculite coverage of 25–30% on the live reef and of 30–40% on the uplifted boulders. Cores taken from living Sinularia revealed a distinct transition from discrete sclerites to compact spiculite and amorphous calcium carbonate cementing the sclerites. In the widespread S. gibberosa, sclerite formation appeared to start intracellularly, followed by a prolonged extracellular calcification process. At the calcification site, multiple sclerocytes formed expanded pseudopod-like membranes that interconnected, forming multicellular vesicles (MCVs) around the sclerites. The MCVs and the pseudopods disappeared at sclerite maturation, followed by degradation of the sclerocytes around the mature sclerites. At the colony base, granular vesicles were distributed among the sclerites, indicating a cementing process in progress. These findings suggest that colonies of Sinularia are able to cement sclerites and consolidate them at their base into spiculite, thus making them reef builders.     

Paradise lost: Mitochondrial eve refuted

Being based solely on neontological data, all «unique parent» evolutionary hypotheses, of which «Mitochondrial Eve» is one, fall into the category ofscala naturae. Mathematical treatment of neontological data bases, using cladistic approaches does not confer the status of scientific hypotheses onto such scenarios. Apart from these fundamental problems, such hypotheses are flawed on a number of other bases, including the fact that there is a proportion of parental contribution to mitochondrial lineages, despite widely publicised statements that mithocondrial DNA in mammals is «strictly» maternally inherited. Other weaknesses of «unique mother» hypotheses on that their proponents endeavour to describe the evolution of diploid organisms on the basis of variability in extant haploid organelles, the evolution of which is delinked from that of the diploid organism. A further difficulty is that it is not possible to reconstruct interspecific relationships on the basis of intraspecific variability. There is a general ignorance among proponents of «unique mother» hypotheses regarding the distribution of biological variability on the surface of the globe, a fact which renders the molecular clock inaccurate, and which upsets the simplistic proposal that molecular diversity equates with time. «Unique mother» scenarios are also invalidated by the presence of shared chromosome and other polymorphisms in african great apes and humans at similar percentages in the different lineages, a fact which indicates that these evolving populations did not experience «bottlenecks». These and other difficulties effectively refute the «Mitochondrial Eve» hypothesis, which in any case much resembles creationism of a special kind, in which the offspring of a breeding pair are visualised as belonging to a species different from its parents. Such extreme examples of the punctuational mode of evolution are highly likely to be incorrect.     

A new species of Ovabunda (Octocorallia,Xeniidae) from the Andaman Sea,Thailand with notes on the biogeography of this genus

A survey of xeniid octocorals was carried out in the waters off Southwestern Thailand in September, 2007. Microscopic investigation of the colonies revealed that three specimens belonged to the genus Ovabunda. Gross morphological examination is presented here accompanied by scanning electron micrographs of the sclerites. Molecular phylogenetic analysis showed identical genotypes at mtMutS, COI, and 28S rDNA for all three specimens and supports their generic assignment. Colony size and shape, sclerite size, and pinnule arrangement differ from nominal species of Ovabunda and thus a new species, O. andamanensis is introduced here. This work also presents a new eastern geographical record for the genus Ovabunda.     

Sclerites in different tissues of Mediterranean Echinodermata

The presence of sclerites in different mesodermal tissues was studied in thirteen species of Mediterranean echinoderms representing the five living classes. In the species of Asteroidea and Crinoidea examined, sclerites were present only in specific tissues. In the species of Ophiuroidea and, especially, Echinoidea and Holothuroidea examined, sclerites were present in almost every tissue, but with considerable variation among species and tissues. Data on sclerite shape, size, and relative abundance (measured as tissue abundance) are presented. The data support the possible functional role of sclerites as reinforcing structures, as well as their possible use as taxonomic characters. Finally, the need of more studies to elucidate the ontogenetic and phylogenetic implications of sclerites is discussed.