Ontogeny of 'epithecal' and septal structures in scleractinian corals

The ontogenetic development of a solitary scleractinian coral, Flabellum distinctum Edwards & Haime, has been studied in serial thin section, with special attention being paid to epithecal nature in relation to septal growth. The term 'epitheca' has been confusingly used for two different skeletal structures: epitheca ( sensu stricto ) and marginotheca. The latter is here newly proposed. 'epitheca' is defined as a calcareous investment developed on the outside of other skeletal structures of a corallite. It can be distinguished from the marginotheca in section by lacking a dark line (calcification centre) and by being unrelated to the formation of septa. 'marginotheca' defines the outer margin of the main skeletal structures of a corallite. It has a dark line which functionally coincides with that of the eutheca. It is of primary origin, preceding formation of septa and provides the origin of the septa. The marginotheca is one of the more important and fundamental skeletal structures for coral classification.     

A restudy of Cystophrentis YÜ, 1931 (Rugosa) from the uppermost Fammenian (Strunian) of South China

The genus Cystophrentis, first described by Yü (1931), occurs in South China, Tibet, Viet Nam and Armenia. Its geological age is Strunian (latest Fammenian). It form the basis for the order Mesocorallia YÜ, 1963, regarded as intermediate between the Rugosa and the Scleractinia based on the presence of metasepta between the counter septum and the counter-lateral septa. The genus Kailingophyllum YU and LIN, 1984 was described as being similar to Cystophrentis, but the apparent differences between these genera are no more than ontogenetic variations. Consequently, Kailingophyllum is regarded here as a synonym of Cystophrentis. Three species from six localities in South China and Tibet are described: Cystophrentis kolaohoensis YÜ, 1931; Cystophrentis simplex (YU and LIN in Yu, Lin and Fan, 1984) and Cystophrentis grandis KUANG in Jia et al., 1977. Serial sections and external septal grooves of the corals studied show no insertion of metasepta between the counter septum and the counter-lateral septa in Cystophrentis. Thus there is no basis for the recognition of the order Mesocorallia YÜ, 1963.© 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

桂西和黔南中三叠世珊瑚

文内描述中三叠世安尼阶(Anisian)珊瑚化石分别采自桂西田阳板纳组和黔南贵阳青岩青岩组。板纳组珊瑚群中建立Pentasmilia guangxiensisgen.etsp.nov.,该新属种有5条第一周期原生隔片甚至有5条第二周期后生隔片,以此不同于有6条第一周期原生隔片和有6条第二周期后生隔片的石珊瑚类(scleractinians)的珊瑚。产于板纳组的另一新属种Radiophyllia astylatusgen.etsp.nov.,其隔片的排列格式与前人归纳的隔片周期插入示意图甚似,但它却发生在中生代最早期(Anisian)珊瑚的骸体内。文中还对青岩组的Pamiroseris silesiaca作了重新描述。     

Regular and flexible modes of division and hystero-ontogenetic growth in the Silurian rugose coral Stauria favosa

New modules arise in colonial corals as the result of asexual reproduction. The Silurian rugosan Stauria favosa ordinarily exhibits cerioid coralla with a characteristic cross-shaped axial structure and a typical pattern of parricidal increase. Quadripartite increase at the sites of the four protosepta is most common, whereas cases of tripartite increase are rare. Parental protosepta are transformed into dividing walls, where the four protosepta first appear with a definite polarity in offset corallites. Daughter corallites inherit metasepta as metasepta, and catasepta as catasepta, within the same quadrants as those of the parent. Metasepta are inserted serially, following Kunth's rule, as is characteristic of rugosan protocorallites. As each daughter corallite derived immediately from the same parent is arranged with identical polarity, it grows equally and evenly both individually and as a group. Daughters thus form protosepta and metasepta under strict phylogenetic and developmental constraints. However, individual corallites grow and reproduce autonomously, by using all available skeleton and space of the parent. Although each module cannot modify essential modes of division, flexibility of the system was via changes in the density and arrangement of corallites, and regulating modes of growth, in tandem with adjacent corallites within the corallum. It is probable that regularity, due to constraints of several origins, as well as flexibility are typical of other rugosan colonies and played an important role in growth dynamics between corallites and corallum.     

Morphology,microstructure, crystallography,and chemistry of distinct CaCO3 deposits formed by early recruits of the scleractinian coral Pocillopora damicornis

Scleractinian corals begin their biomineralization process shortly after larval settlement with the formation of calcium carbonate (CaCO₃) structures at the interface between the larval tissues and the substrate. The newly settled larvae exert variable degrees of control over this skeleton formation, providing an opportunity to study a range of biocarbonate structures, some of which are transient and not observed in adult coral skeletons. Here we present a morphological, structural, crystallographic, and chemical comparison between two types of aragonite deposits observed during the skeletal development of 2‐days old recruits of Pocillopora damicornis: (1) Primary septum and (2) Abundant, dumbbell‐like structures, quasi‐randomly distributed between initial deposits of the basal plate and not present in adult corals—At the mesoscale level, initial septa structures are formed by superimposed fan‐shaped fasciculi consisting of bundles of fibers, as also observed in adult corals. This organization is not observed in the dumbbell‐like structures. However, at the ultrastructural level there is great similarity between septa and dumbbell components. Both are composed of <100 nm granular units arranged into larger single‐crystal domains.Chemically, a small difference is observed between the septae with an average Mg/Ca ratio around 11 mmol/mol and the dumbbell‐like structures with ca. 7 mmol/mol; Sr/Ca ratios are similar in the two structures at around 8 mmol/mol—Overall, the observed differences in distribution, morphology, and chemistry between septa, which are highly conserved structures fundamental to the architecture of the skeleton, and the transient, dumbbell‐like structures, suggest that the latter might be formed through less controlled biomineralization processes. Our observations emphasize the inherent difficulties involved in distinguishing different biomineralization pathways based on ultrastructural and crystallographical observations. J. Morphol. 276:1146–1156, 2015. © 2015 Wiley Periodicals, Inc.     

Microstructural characteristics of the stony coral genus Acropora useful to coral reef paleoecology and modern conservation

Identification of fossil corals is often limited due to poor preservation of external skeleton morphology, especially in the genus Acropora which is widespread across the Indo‐Pacific. Based on skeleton characteristics from thin section, we here develop a link between the internal skeleton structure and external morphology. Ten characteristics were summarized to distinguish Acropora and five related genera, including the type and differentiation of corallites, the skeleton nature of corallites (septa, columellae, dissepiments, wall), and calcification centers within septa. Acropora is distinctive for its dimorphic corallites: axial and radial. Isopora is similar to Acropora but possess more than a single axial corallites. Montipora and Astreopora (family Acroporidae) have monomorphic corallites and a synapticular ring wall, with clustered calcification center in the former and medial lines in the latter. Pocillopora and Porties are classified by distinctive dissepiments, columellae and septa. These microstructural skeleton characteristics were effective in the genus identification of fossil corals from drilled cores in the South China Sea. Eighteen detailed characteristics (ten of axial corallites, four of radial corallites, and four of coenosteum) were used in the Acropora species classification. The axial corallites size and structure (including corallite diameter, synapticular rings, and septa), the septa of radial corallites, and the arrangement of coenosteum were critical indicators for species identification. This identification guide can help paleoenvironmental and paleoecological analyses and modern coral reef conservation and restoration.     

Anatomy and phylogenetic significance of Eoconularia loculata, a conulariid from the Silurian of Gotland

The type material of Eoconularia loculata (Wiman, 1895), a conulariid with high, bifurcated septa, was originally found in an erratic boulder, hence the source-rock is as yet unidentified. Recently, a rich material of the species has been discovered at eleven localities in the Silurian Hemse Beds of Gotland Another two localities in the Slite Beds (Wenlockan, Sheinwoodian) revealed what is assumed to be the ancestor of E loculata. This ancestral form probably constitutes a separate taxon distinguished from E. loculata in having simple, unbranched septa. E. loculata is re-described, and four ontogenetic stages in septal development are recognized. During stage 1, the most juvenile stage, the septa are simple. The septa in stages 3 and 4, the adult stages, are coarse and bifurcated. The affinities of conulariids are discussed, with the conclusion that the group shares a number of similarities with modem scyphomans. The microstructures of the exoskeleton show several similarities with coronatids, and the septa are interpreted to be homologous with the internal structures of stauromedusids. The stratigraphical distribution of all currently known septate conulariids suggests that septa were a primitive morphologic feature ranging from early? Ordovician to late Silurian. The simplest type, however, persisted at least into the early Permian. Five of the eleven described septa types have been found only among the conulariids from Gotland. □Conulariida, EOCONULARIA LOCULATA, bifurcated septa, taxonomy, ecology, morphology, Scyphozoa, Sweden, Gotland, Silurian.     

Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula

Sentoku, A. & Ezaki, Y. 2011: Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula. Lethaia, Vol. 45, pp. 62–70. Scleractinia display a variety of growth forms, whether zooxanthellate or azooxanthellate, as the consequence of the combined effects of both intrinsic and extrinsic factors. New modules arise in colonial corals through asexual reproduction, including budding and division. The azooxanthellate, branching dendrophylliid Dendrophyllia arbuscula van der Horst 1922 , is a good species to investigate intrinsic regularities in budding, because: (1) the lateral corallites always occur in the vicinity of four primary septa, excluding the two directive primary septa; (2) the two directive septa in lateral corallites tend to be oriented almost perpendicular to the growth orientation of parental corallites; (3) the lateral corallites grow more‐or‐less diagonally upwards; and (4) these regularities are retained from the axial to the derived lateral corallites during colony growth. Accordingly, a colony of apparently complex dendroid corals is formed according to certain universal rules that apply to successive generations of corallites. The presence of two opposite sectors in which budding do not occur seems to be common to other azooxanthellate scleractinian families. Regularities, other than the orientation of the directive septa, are also commonly found at least in other azooxanthellate dendrophylliid genera. These regularities suggest the presence of strict developmental constraints on the asexual reproduction of the Scleractinia, both extant and extinct. These regularities by azooxanthellate scleractinians, as one of the representative colonial metazoan groups, provide us with fundamental data with which we can understand how colonies are constructed. □Azooxanthellate coral, budding, colony, Dendrophyllia arbuscula, regularity.     

Early heliolitine tabulate corals from the Sandbian (Upper Ordovician) in the Yunnan-Sichuan border area,Southwest China

Heliolitine tabulate corals are extremely rare in pre-Katian (Upper Ordovician) rocks worldwide, hindering the understanding of their origin and early evolution. Here, we systematically study new heliolitine material from the upper member (Sandbian) of the Huadan Formation in the Yunnan-Sichuan border area, Southwest China, which includes Protaraea ningnanensis, Plasmoporella kiaeri, Wormsipora sp. and Heliolites spinosus. The findings indicate that Protaraea and Heliolites are ancestral forms of coccoserids and typical tubular heliolitines, respectively, and that the absence of trabecular septa is probably a primitive feature of plasmoporellids. The refined Ordovician stratigraphy of this area implies that the coccoserid Protaraea ningnanensis Lin, 1965 from the lower member (late Darriwilian) of the Huadan Formation is the earliest known heliolitine, which further indicates that all heliolitines might have evolved from Protaraea. The comparison of Protaraea with other early tabulate corals also suggests an independent heliolitine origin from auloporinids and sarcinulinids.     

Evidence and structural mechanism for late lung alveolarization

According to the current view, the formation of new alveolar septa from preexisting ones ceases due to the reduction of a double- to a single-layered capillaries network inside the alveolar septa (microvasculature maturation postnatal days 14-21 in rats). We challenged this view by measuring stereologically the appearance of new alveolar septa and by studying the alveolar capillary network in three-dimensional (3-D) visualizations obtained by high-resolution synchrotron radiation X-ray tomographic microscopy. We observed that new septa are formed at least until young adulthood (rats, days 4-60) and that roughly half of the new septa are lifted off of mature septa containing single-layered capillary networks. At the basis of newly forming septa, we detected a local duplication of the capillary network. We conclude that new alveoli may be formed in principle at any time and at any location inside the lung parenchyma and that lung development continues into young adulthood. We define two phases during developmental alveolarization. Phase one (days 4-21), lifting off of new septa from immature preexisting septa, and phase two (day 14 through young adulthood), formation of septa from mature preexisting septa. Clinically, our results ask for precautions using drugs influencing structural lung development during both phases of alveolarization.     

The function of the brachial valve septa in plectambonitacean brachiopods

Eoplectodonta transversalis (Wahlcnberg) and other sowcrbyellids have a complex arrangement of septa in the brachial valve. It is argued that the function of these is primarily to support the lophophore and to strengthen the shell, and that the septa mirror is almost exactly the shape of the lophophore. In Eoplectodonta transversalis the ontogenetic develop ment of the lophophore varies from a simple to a complcx ptycholophe. Other plectam-bonitaceans have trocholophous and schizolophous lophophores.     

Soft body reconstructions of Palaeozoic corals: implications for the system of Anthozoa (Coelenterata)

The soft bodies and individual developmental sequences of the polyps of Palaeozoic corals are reconstructed on the basis of the functional, engineering and constructional morphology of Recent Anthozoa. Four types of body construction can be distinguished by the arrangement of mesenteries, the number of mesentery insertion zones and characteristic septal insertion patterns: (1) serial insertion of single mesenteries in four sectors, which has resulted in the serial insertion of septa, (2) symmetrical insertion of single mesenteries in four sectors, which has resulted in a symmetrical septal pattern or pseudo radial septal patterns, (3) exponential insertion of paired mesenteries in four sectors, which has resulted in septa bifurcation, and (4) exponential insertion of paired mesenteries in six sectors, which has resulted in a radial septal pattern. Suggestions for a constructional taxonomy are given on the basis of the arrangement of mesenteries and on individual development of the reconstructed polyps. Accordingly, new superorders are introduced: 'Seriales' for the first body construction and 'Symmetricales' for the second. The third body construction is that of the Heterocorallia and the fourth that of the Hexacorallia. Following a constructional taxonomy, new and stricter definitions are given for the new and already known taxonomic categories of Rugosa, Heterocorallia and Hexacorallia. A byproduct of this re-definition is that several Palaeozoic corals represent the body construction of the Hexacorallia and should therefore be revised as Hexacorallia; consequently, Hexacorallia must already have been present in the Palaeozoic.     

Fine-Scale Skeletal Banding Can Distinguish Symbiotic from Asymbiotic Species among Modern and Fossil Scleractinian Corals

Understanding the evolution of scleractinian corals on geological timescales is key to predict how modern reef ecosystems will react to changing environmental conditions in the future. Important to such efforts has been the development of several skeleton-based criteria to distinguish between the two major ecological groups of scleractinians: zooxanthellates, which live in symbiosis with dinoflagellate algae, and azooxanthellates, which lack endosymbiotic dinoflagellates. Existing criteria are based on overall skeletal morphology and bio/geo-chemical indicators—none of them being particularly robust. Here we explore another skeletal feature, namely fine-scale growth banding, which differs between these two groups of corals. Using various ultra-structural imaging techniques (e.g., TEM, SEM, and NanoSIMS) we have characterized skeletal growth increments, composed of doublets of optically light and dark bands, in a broad selection of extant symbiotic and asymbiotic corals. Skeletons of zooxanthellate corals are characterized by regular growth banding, whereas in skeletons of azooxanthellate corals the growth banding is irregular. Importantly, the regularity of growth bands can be easily quantified with a coefficient of variation obtained by measuring bandwidths on SEM images of polished and etched skeletal surfaces of septa and/or walls. We find that this coefficient of variation (lower values indicate higher regularity) ranges from ~40 to ~90% in azooxanthellate corals and from ~5 to ~15% in symbiotic species. With more than 90% (28 out of 31) of the studied corals conforming to this microstructural criterion, it represents an easy and robust method to discriminate between zooxanthellate and azooxanthellate corals. This microstructural criterion has been applied to the exceptionally preserved skeleton of the Triassic (Norian, ca. 215 Ma) scleractinian Volzeia sp., which contains the first example of regular, fine-scale banding of thickening deposits in a fossil coral of this age. The regularity of its growth banding strongly suggests that the coral was symbiotic with zooxanthellates.     

Morphological diversification of fish as a consequence of the divergence of ontogenetic trajectories]

The possibilities of the investigation of ontogenetic changes in the morphological features of fish using multidimensional "ontogenetic channels," within which individual ontogenetic trajectories run, are demonstrated using African barbs. (Barbus intermedius complex) as an example. The position of ontogenetic channels allows one to judge how the differences of adult individuals in morphological characters arise during development and how their morphological diversity is formed.     

Floral development of Justicia gendarussa (Acanthaceae)

The sequence of primordial initiation is acropetal and the primordia develop in the same order in which they appear. The floral apex has a two-layered tunica in all stages of development. There is no significant difference in the initiation of any of the floral appendages and thus all floral organs are homologous with respect to their histogenetic origin. The short calyx tube is formed by ontogenetic fusion of the bases of sepals; but the corolla tube arises partly by ontogenetic union of originally free parts and partly by zonal or intercalary growth. Each primordium receives a single procambium strand shortly after its initiation, except those of the posterior pair of stamens, which do not receive any vascular supply. This provides another example which goes against the doctrine of "conservatism of vascular bundles". The placentation in Justicia is parietal ontogenetically as well as anatomically.     

西藏晚二叠世四射珊瑚Ipciphyllum naoticum的鳞板特征兼论喷口构造的分类意义

Ipciphyllum是中国中晚二叠世地层中最常见的块状复体四射珊瑚, Ipciphyllum naoticum是该属中唯一发育喷口构造的种。通过对采自西藏札达姜叶玛剖面上二叠统姜叶玛组的Ipciphyllum naoticum进行连续切片, 研究其鳞板特征, 发现横切面上鳞板形态在个体发育的不同阶段变化明显, 包括喷口(庙宇状)鳞板、弧形板片状鳞板和偶现的侧鳞板等, 表明同一种内鳞板的形态多变, 以某一特殊形态的鳞板作为种一级甚至更高级的分类标准值得商榷。结合前人对喷口鳞板的发育可能与相对高能的水环境有关, 分类意义不应超过种级的研究结论等, 建议废除以喷口鳞板(构造)作为重要分类特征的Protonaoticophylidae科和Protonaoticophylinae亚目。     

Importance of live coral habitat for reef fishes

Live corals are the key habitat forming organisms on coral reefs, contributing to both biological and physical structure. Understanding the importance of corals for reef fishes is, however, restricted to a few key families of fishes, whereas it is likely that a vast number of fish species will be adversely affected by the loss of live corals. This study used data from published literature together with independent field based surveys to quantify the range of reef fish species that use live coral habitats. A total of 320 species from 39 families use live coral habitats, accounting for approximately 8 % of all reef fishes. Many of the fishes reported to use live corals are from the families Pomacentridae (68 spp.) and Gobiidae (44 spp.) and most (66 %) are either planktivores or omnivores. 126 species of fish associate with corals as juveniles, although many of these fishes have no apparent affiliation with coral as adults, suggesting an ontogenetic shift in coral reliance. Collectively, reef fishes have been reported to use at least 93 species of coral, mainly from the genus Acropora and Porities and associate predominantly with branching growth forms. Some fish associate with a single coral species, whilst others can be found on more than 20 different species of coral indicating there is considerable variation in habitat specialisation among coral associated fish species. The large number of fishes that rely on coral highlights that habitat degradation and coral loss will have significant consequences for biodiversity and productivity of reef fish assemblages.     

Structure of the body cavity of the sea spider <Emphasis Type="Italic">Nymphon brevirostre</Emphasis> Hodge, 1863 (Arthropoda: Pycnogonida)

The microscopic anatomy and ultrastructure of the body cavity and adjacent organs in the sea spider Nymphon brevirostre Hodge, 1863 (Pycnogonida, Nymphonidae) were examined by transmission electron microscopy. The longitudinal septa subdividing the body cavity are described: (1) Dohrn’s horizontal septum, (2) lateral heart walls, and (3) paired ventral septa consisting of separate cellular bands. The body cavity is a hemocoel, it has no epithelial lining and is only bordered by a basal lamina. The epidermis, heart, and Dohrn’s septum are not separated from each other by basal laminae and may have a common origin. The cellular bands forming the longitudinal ventral septa are not covered with the basal lamina and presumably derive from cells belonging to the hemocoel. The roles of the morphological structures studied for the circulation of hemolymph are discussed. The gonad lies inside Dohrn’s septum, it is covered with its own basal lamina and surrounded by numerous lacunae of the hemocoel entering the septum. The gonad wall is formed with a single layer of epithelium. The same epithelial cells form the gonad stroma. The gonad cavity is not lined with the basal lamina; muscle cells are present in the gonad wall epithelium, thus rendering the lumen similar to a coelomic cavity. Freely circulating cells of two types are found in the hemocoel: small amebocytes containing electronic-dense granules that are similar to granulocytes of other arthropods, as well as hemocytes with large vacuoles of varying structure that are comparable with plasmatocytes; however some of these may be activated granulocytes.     

Variation in skeletal microstructure of the coral Galaxea fascicularis: effects of an aquarium environment and preparatory techniques

To compare the crystalline microstructure of exsert septa, polyps of the scleractinian coral Galaxea fascicularis were sampled from shallow reef flat colonies, from colonies living at a depth of 9 m, and from colonies kept in a closed-circuit aquarium. Septal crystal structure and orientation was markedly different between corals in the field and in aquaria. In samples collected from deep water, acicular crystals were composed of conglomerates of finer crystals, and skeletal filling was considerably reduced when compared with samples collected from shallow water. Comparisons were also made between septa prepared in sodium hypochlorite (commercial bleach), sodium hydroxide (NaOH), hydrogen peroxide (H(2)O(2)), and distilled water (dH(2)O). Commercial bleach was the most effective solvent for tissue dissolution in investigations of skeletal structure. Samples prepared in NaOH commonly displayed crystalline artefacts, while the use of dH(2)O and H(2)O(2) was labor intensive and often resulted in unclean preparations. Fusiform crystals were seen only on G. fascicularis septa prepared in bleach and on Acropora formosa axial corallites prepared in either bleach or dH(2)O. We suggest that the mechanical agitation and additional washing necessary for samples prepared in dH(2)O, NaOH, or H(2)O(2) resulted in the loss of fusiform crystals from these preparations.     

Minireview: On the homology of the protocoel in Cephalochordata and 'lower' Deuterostomia

Hypotheses regarding the homology of the protocoel in planktonic deuterostome larvae and mesodermal structures in ontogenetic stages of cephalochordates are evaluated. The prevalent ‘classical’ hypothesis describes the protocoel as being homologous with the diverticula of Hatschek, which, on the left side, develop into the preoral pit, subsequently into Hatschek’s pit and groove (in part). This hypothesis is based mainly on the position of Hatschek’s diverticula anterior to the rest of the mesoderm during their enterocoelic origin. It is shown here that during development the mesodermal segment that develops into Hatschek’s nephridium is the most anterior one prior to formation of Hatschek’s diverticula, and this segment assumes an anteriormost position after differentiation of Hatschek’s diverticula. Additional similarities between this segment and protocoels are: (i) presence of endomesodermal cells with podocytic extensions, (ii) excretory function, (iii) relatively early ontogenetic origin, (iv) probable lack of association with nervous structures, (v) probable ectodermal origin of a portion of the canal, and (vi) position relative to the mouth opening. Therefore, homology between the protocoel and the segment that becomes Hatschek’s nephridium is proposed. It is concluded that a glandular structure homologous to the diverticula of Hatschek and anterior to the protocoel/Hatschek’s nephridium is a synapomorphy of notochordates or chordates.