Calcium Transport along the Axial Canal in Acropora

In Acropora, the complex canals in a coral colony connect all polyps to a holistic network, enabling them to collaborate in performing biological processes. There are various types of canals, including calice, axial canals, and other internal canals, with structures that are dynamically altered during different coral growth states due to internal calcium transport. In this study, we investigated the morphological changes in the corallite of six Acropora muricata samples by high resolution micro-computed tomography, observing the patterns of calcium carbonate deposition within axial corallite during processes of new branch formation and truncated tip repair. We visualized the formation of a new branch from a calice and the calcium carbonate deposition in the axial canal. Furthermore, the diameter and volume changes of the axial canal in truncated branches during rebuilding processes were calculated, revealing that the volume ratio of calcareous deposits in the axial canal exhibit significant increases within the first three weeks, returning to levels in the initial state in the following week. This work demonstrates that calcium carbonate can be stored temporarily and then remobilized as needed for rapid growth. The results of this study shed light on the control of calcium carbonate deposition and growth of the axial corallite in Acropora.

Calcium Transport along the Axial Canal in Acropora

In Acropora, the complex canals in a coral colony connect all polyps into a holistic network to collaborate in performing biological processes. There are various types of canals, including calice, axial canals, and other internal canals, with structures that are dynamically altered during different coral growth states due to internal calcium transport. However, few studies have considered the regulation of calcium transport in Acropora. In this study, we investigated the morphological changes of the axial canal in six Acropora muricata samples by high resolution micro-computed tomography, observing the patterns of the axial canal during the processes of new branch formation and truncated branch rebuilding. We visualized the formation of a new branch from a calice and deposition of the iconic hexactin skeletons in the axial canal. Furthermore, the diameter and volume changes of the axial canal in truncated branches during rebuilding processes were calculated, revealing that the volume ratio of calcareous deposits in the axial canal exhibit significant increases within the first three weeks, returning to levels in the initial state in the following week. This work indicates that the axial canal can transport calcium to form hexactin skeletons in a new branch and rebuild the tip of a truncated branch. The calcium transport along canal network regulates various growth processes, including budding, branching, skeleton forming, and self-rebuilding of an Acropora colony. Understanding the changes in canal function under normal and extreme conditions will provide theoretical guidance for restoration and protection of coral reefs.

Axial Canal Regulates the Processes of Coral Branching and Calcareous Transportation in Acropora

In Acropora, the complex canals in a coral colony connect all polyps into a holistic network to collaborate in performing biological processes, while axial canal is the largest canal amongst the network and distributes at the center of a coral branch. However, previous studies indicated that, in the non-radial symmetry transport system of Acropora, axial canal do not play a major role in the transport of hydroplasm, and the action of axial canal in coral growth is still obscure. In this study, we reconstructed six Acropora muricata samples by high resolution micro-computed tomography to investigate the growth patterns of axial canals during the processes of new branch forming and truncated branch rebuilding. We found that the axial canal of a new branch is transformed from a calice and the polyps in the new branch are budded from the polyp in the axial canal. Meanwhile, the axial canal can transport the calcareous skeletons to rebuild the tip of a truncated branch, which represents as the change in the diameter of axial canal and calcareous deposition/reduction in it. This work indicate the regulation of axial canal in the growth processes including budding, branching, and mineralising of an Acropora colony.

The Largest Bio-Silica Structure on Earth: The Giant Basal Spicule from the Deep-Sea Glass SpongeMonorhaphis chuni

The depth of the ocean is plentifully populated with a highly diverse fauna and flora, from where the Challenger expedition (1873–1876) treasured up a rich collection of vitreous sponges [Hexactinellida]. They have been described by Schulze and represent the phylogenetically oldest class of siliceous sponges [phylum Porifera]; they are eye-catching because of their distinct body plan, which relies on a filigree skeleton. It is constructed by an array of morphologically determined elements, the spicules. Later, during the German Deep Sea Expedition “Valdivia” (1898-1899), Schulze could describe the largest siliceous hexactinellid sponge on Earth, the up to 3 m highMonorhaphis chuni, which develops the equally largest bio-silica structures, the giant basal spicules (3 m × 10 mm). With such spicules as a model, basic knowledge on the morphology, formation, and development of the skeletal elements could be elaborated. Spicules are formed by a proteinaceous scaffold which mediates the formation of siliceous lamellae in which the proteins are encased. Up to eight hundred 5 to 10 μm thick lamellae can be concentrically arranged around an axial canal. The silica matrix is composed of almost pure silicon and oxygen, providing it with unusual optophysical properties that are superior to those of man-made waveguides. Experiments indicated that the spicules functionin vivoas a nonocular photoreception system. In addition, the spicules have exceptional mechanical properties, combining mechanical stability with strength and stiffness. Like demosponges the hexactinellids synthesize their silica enzymatically, via the enzyme silicatein. All these basic insights will surely contribute also to a further applied utilization and exploration of bio-silica in material/medical science.

The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review

Sponges (phylum Porifera) had been considered as an enigmatic phylum, prior to the analysis of their genetic repertoire/tool kit. Already with the isolation of the first adhesion molecule, galectin, it became clear that the sequences of sponge cell surface receptors and of molecules forming the intracellular signal transduction pathways triggered by them, share high similarity with those identified in other metazoan phyla. These studies demonstrated that all metazoan phyla, including Porifera, originate from one common ancestor, the Urmetazoa. The sponges evolved prior to the Ediacaran-Cambrian boundary (542 million years ago [myr]) during two major "snowball earth events", the Sturtian glaciation (710 to 680 myr) and the Varanger-Marinoan ice ages (605 to 585 myr). During this period the ocean was richer in silica due to the silicate weathering. The oldest sponge fossils (Hexactinellida) have been described from Australia, China and Mongolia and are thought to have existed coeval with the diverse Ediacara fauna. Only little younger are the fossils discovered in the Sansha section in Hunan (Early Cambrian; China). It has been proposed that only the sponges possessed the genetic repertoire to cope with the adverse conditions, e.g. temperature-protection molecules or proteins protecting them against ultraviolet radiation. The skeletal elements of the Hexactinellida (model organisms Monorhaphis chuni and Monorhaphis intermedia or Hyalonema sieboldi) and Demospongiae (models Suberites domuncula and Geodia cydonium), the spicules, are formed enzymatically by the anabolic enzyme silicatein and the catabolic enzyme silicase. Both, the spicules of Hexactinellida and of Demospongiae, comprise a central axial canal and an axial filament which harbors the silicatein. After intracellular formation of the first lamella around the channel and the subsequent extracellular apposition of further lamellae the spicules are completed in a net formed of collagen fibers. The data summarized here substantiate that with the finding of silicatein a new aera in the field of bio/inorganic chemistry started. For the first time strategies could be formulated and experimentally proven that allow the formation/synthesis of inorganic structures by organic molecules. These findings are not only of importance for the further understanding of basic pathways in the body plan formation of sponges but also of eminent importance for applied/commercial processes in a sustainable use of biomolecules for novel bio/inorganic materials.

The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review

Sponges (phylum Porifera) had been considered as an enigmatic phylum, prior to the analysis of their genetic repertoire/tool kit. Already with the isolation of the first adhesion molecule, galectin, it became clear that the sequences of the sponge cell surface receptors and those of the molecules forming the intracellular signal transduction pathways, triggered by them, share high similarity to those identified in other metazoan phyla. These studies demonstrated that all metazoan phyla, including the Porifera, originate from one common ancestor, the Urmetazoa. The sponges evolved during a time prior to the Ediacaran-Cambrian boundary (542 million years ago (myr)). They appeared during two major "snowball earth events", the Sturtian glaciation (710 to 680 myr) and the Varanger-Marinoan ice ages (605 to 585 myr). During this period the aqueous milieu was silica rich due to the silicate weathering. The oldest sponge fossils (Hexactinellida) have been described from Australia, China and Mongolia and were assessed to have existed coeval with the diverse Ediacara fauna. Only little younger are the fossils discovered in the Sansha section in Hunan (Early Cambrian; China). It has been proposed that only the sponges had the genetic repertoire to cope with the adverse conditions, e.g. temperature-protection molecules or proteins protecting them against ultraviolet radiation. The skeletal elements of the Hexactinellida (model organisms Monorhaphis chuni and Monorhaphis intermedia or Hyalonema sieboldi) and Demospongiae (models Suberites domuncula and Geodia cydonium), the spicules, are formed enzymatically by the anabolic enzyme silicatein and the catabolic enzyme silicase. Both, the spicules of Hexactinellida and of Demospongiae, comprise a central axial canal and an axial filament which harbors the silicatein. After intracellular formation of the first lamella around the channel and the subsequent extracellular apposition of further lamellae the spicules are completed in a net formed of collagen fibers. The data summarized here substantiate that with the finding of silicatein a new aera in the field of bio/inorganic chemistry started. For the first time strategies could be formulated and experimentally proven that allow the formation/synthesis of inorganic structures by organic molecules. These findings are not only of importance for the further understanding of basic pathways in the body plan formation of sponges but also of eminent importance for applied/commercial processes in a sustainable use of biomolecules for novel bio/inorganic materials.

Quintuplexacrinus, a new cladid crinoid genus from the Upper Ordovician Maquoketa Formation of the northern midcontinent of the United States

Quintuplexacrinusnew genus withDendrocrinus oswegoensisMeek and Worthen (1868) as the type and only known species is described and assigned to the Merocrinidae. The new genus is characterized by a unique stem with a highly pentalobate axial canal; the distal column is highly differentiated with large and very high nodals and thin intemodals. A cladistic analysis indicates thatQuintuplexacrinusn. gen. is closely related toPraecupulocrinus.The numbers of the various orders of brachs are independent of the size and age of the animals. Within the arms only the numbers of primibrachs and secundibrachs are positively correlated. Some variation is related to position of the rays. The C ray bears the smallest number of primibrachs. The outer half-rays possess more numerous tertibrachs than the inner ones. Aboral cup growth produces a wide-based and distally expanding outline at all sizes. In general, the widths of the cup and the cup's component plates are positively allometric relative to their heights. Likewise, the width: height ratios of the proximal brachs, primibrachs through tertibrachs, increase in older and larger individuals because the widths grow faster than the heights. The number of columnals in both the proximal and distal stem regions is typically stabilized throughout ontogeny. However, the entire stem becomes longer and wider in larger specimens due to calcite deposition on the columnals. Development of the columnals is isometric so their shapes do not change with size and age.

Fossil Hexactinellida

The structure and evolution of the hexactinellid skeleton has been conditioned by: (1) the rectangular form of the spicule (ultimately due to the square cross-section of the axial canal), and (2) the sheet-like form of the choanocyte-membrane, properly the choano-syncytium (Reiswig, 1979) as individual choanocytes with proper nuclei do not exist, which is a continuous syncytial sheet bearing outpocketings (diverticula) that correspond to the choanocyte chambers of other sponge groups. In most species the diverticula are separate, and attached to one another by syncytial filaments, but their arrangement as part of a sheet-like structure is still apparent. In a few species the choanocyte membrane becomes a labyrinth of anastomosing tubes. Accompanying these are the essential absence of mesogloea and the paucity of collagen (spongin), which results in the soft parts being essentially confined to the space occupied by the skeleton. The place of mesogloea is taken by a syncytial network of filaments which also form the dermal and gastral membranes.

Modern Hexactinellida

Hexactinellid sponges have a skeleton made up basically of six-rayed spicules occurring individually or fused together by supplementary secretions of silicon dioxide to form a rigid latticelike or reticulate skeleton. Microscleres of one of two basic types are always present. The axial canal of hexactinellid spicules is square in cross section.

The Morphology and Physiology of the Salivary Glands of Hemiptera-Heteroptera

The salivary glands of the Heteroptera consist of a pair of primarily bilobed principal glands and accessory glands which vary very greatly in form and structure in different families. The glands are usually supplied with tracheae, and the principal glands are invested by a nervous plexus which is supplied by a glandular nerve from the hypocerebral ganglion of the stomatogastric system. The principal salivary gland of Notonecta is characterized by the presence of large cells having zymogen granules and by the storage of fluid secretion in vacuoles. In contrast, most of the remaining Heteropteran salivary glands belong to the vesicular type, having a one-layered glandular epithelium made up of small cells which discharge their secretion into a large central storage cavity or axial canal. This type of gland lacks zymogen granules but has small dense masses of reserve material in the basal or outer parts of the cells. There is normally no difference in the structure of the glandular epithelium in the different lobes. The accessory glands are either in the form of a thin-walled bladder-like vesicle, or are tubular or duct-like; they seem to be purely a development of the primary conducting glandular system, and are thus homologous with the salivary reservoir of other orders. All the information obtained in this work is strongly against the idea that the various lobes of Hemipterous salivary glands produce widely different chemical substances, each with a special function. The results obtained by Fauré-Fremiet have not been confirmed. Except with blood-sucking forms digestive enzymes were always found in the glands, two enzymes being the maximum number found in any particular gland. The enzymes were found to be always related to the type of food consumed, and were those concerned with the digestion of that particular component of the food which was present in the greatest proportion. In no case was a cellulase found. An anti-coagulant principle was found to be present in the glands of blood-sucking forms. The accessory glands appear to produce only a watery secretion, enzymes being absent. The pH of the principal gland is generally slightly acid, while that of the accessory gland is neutral. Mitochondria and Golgi bodies typical of insect tissue are present in certain glands, but show no relation to the secretion granules, and thus do not appear to contribute to secretion synthesis. From a number of experiments it appears that the action of the digestive enzymes is not sufficiently rapid for external digestion to take place to any great extent. It seems, however, certain that quite an appreciable quantity of the injected saliva is imbibed again, and that the salivary digestion continues in the stomach, where the food taken in is first stored. The pH activity range of the enzymes is in general wide.