Peculiar digestion patterns of sponge-associated zoochlorellae in the caddisfly Ceraclea fulva

The caddisfly Ceraclea fulva feeds exclusively on the freshwater sponge Ephydatia fluviatilis. Sponge spicules are accumulated in the insect midgut and arranged perpendicularly to the longitudinal axis of its gut. The peritrophic membrane of the midgut is so thick that it prevents spicules from damaging the epithelium during their transit. The digestion process of the endocellular zoochlorellae, which are vehiculated by the sponge cells, was examined by transmission electron microscopy (TEM). Zoochlorellae were seen in the midgut lumen, close to the peritrophic membrane and in the underlying space. Discrete algal cells became evident in tight apposition to the brush border of the midgut cells and were enveloped by the microvilli. Digestion progressed to the final transformation of the organism into membrane-delimited vacuoles.     

Light inside sponges

Sponges are the most basal metazoan organisms. As sessile filter feeders in marine or freshwater habitats, they often live in close association with phototrophic microorganisms. Active photosynthesis by the associated microorganisms has been believed to be restricted to the outer tissue portion of the sponge hosts. However, phototrophic microorganisms have also been detected in deeper tissue regions. In many cases they are found around spicules, siliceous skelettal elements of demosponges and hexactinellids. The finding of phototrophic organisms seemingly assembled around spicules led to the hypothesis of a siliceous light transmission system in sponges. The principle ability to conduct light was already shown for sponge derived, explanted spicules. However it was not shown until now, that in deed sponges have a light transmission system, and can harbour photosynthetically active microorganisms in deeper tissue regions.Here we show for the first time, that, as hypothesized 13 year ago, sponge spicules in living specimens transmit light into deeper tissue regions. Our results demonstrate that in opposite to the actual opinion, photosynthetically active microorganisms can also live in deeper tissue regions, and not only directly beneath the surface, when a light transmission system (spicules) is present.Our results show the possibility of massive or globular sponges being supplied with photosynthetic products or pathways throughout their whole body, implying not only a more important role of these endobioses. Our findings also elucidate the in-situ function of a recently more and more interesting biomaterial, which is unique not only for its mechanical, electrical and optical properties. Biosilica is of special interest for the possibility to produce it enzymatically under environmental conditions.     

Resilience of aquatic net‐spinning caddisfly silk structures to common global stressors

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Spicules of hexactinellid sponges (Hexactinellida: Porifera) as natural composite materials

This paper reviews studies on the hexactinellid glass sponges (Hexactinellida: Porifera) that have organic silica spicules. According to its physical properties (microdensity, Young’s modulus, and light transmission), the material of the spicules is similar to amorphous silica; however, sponge spicules are birefringent, which suggests that they have a highly ordered crystal-like nature. Mineralized remnants of siliceous spicules composed of chemically inert materials are preserved in sedimentary rocks and provide evidence of the ecological state of the ancient biosphere. Sponges occur in waters with low temperatures; therefore, they grow very slowly and live for hundreds of years. The organic silica spicules exhibit the capacity for triboluminescence. The generated light emission may be used by symbiotic bacteria on the spicule surface.     

Ultrastructure of siliceous spicules and microsclerocytes in the marine sponge Neofibularia irata N. SP.

The marine sponge Neofibularia irata contains four different categories of siliceous spicules. These spicules are evident in the tissues as distinct bundles that act to increase the structural rigidity of the sponge. All spicules have a normal structural morphology with silica deposition around a hexagonal axial canal containing a crystalline axial filament. The megasclere strongyles are secreted in typical megasclerocytes. The sigma and raphid microscleres are secreted in individual microsclerocytes that are grouped together in parallel to form loose bundles. However, the microxea microscleres are apparently secreted in distinct tight bundles (trichodragmas) within a single cell. These cells, containing between 13 and 39 spicules, are grouped to form large packets of bundles of spicules.     

Histological investigation of organisms with hard skeletons: a case study of siliceous sponges.

Siliceous and calcareous sponges commonly are treated with acid to remove the spicules prior to embedding and cutting for histological investigations. Histology of spiculated sponge tissue represents a challenging problem in sponge histotechnology. Furthermore, fluorescence in situ hybridization (FISH), a key method for studying sponge-associated microbes, is not possible after acid treatment. For a broad range of siliceous sponge species, we developed and evaluated methods for embedding in paraffin, methylmethacrylate resins, LR White resin and cryomatrix. Different methods for cutting tissue blocks as well as mounting and staining sections also were tested. Our aim was to enable histological investigations and FISH without prior removal of the spicules. To obtain an overview of tissue and skeleton arrangement, we recommend embedding tissue blocks with LR White resin combined with en bloc staining techniques for large specimens with thick and numerous spicules, but paraffin embedding and subsequent staining for whole small specimens. For FISH on siliceous sponges, we recommend Histocryl embedding if the spicule content is high, but paraffin embedding if it is low. Classical histological techniques are used for detailed tissue examinations.     

Histological investigation of organisms with hard skeletons: a case study of siliceous sponges

Siliceous and calcareous sponges commonly are treated with acid to remove the spicules prior to embedding and cutting for histological investigations. Histology of spiculated sponge tissue represents a challenging problem in sponge histotechnology. Furthermore, fluorescence in situ hybridization (FISH), a key method for studying sponge-associated microbes, is not possible after acid treatment. For a broad range of siliceous sponge species, we developed and evaluated methods for embedding in paraffin, methylmethacrylate resins, LR White resin and cryomatrix. Different methods for cutting tissue blocks as well as mounting and staining sections also were tested. Our aim was to enable histological investigations and FISH without prior removal of the spicules. To obtain an overview of tissue and skeleton arrangement, we recommend embedding tissue blocks with LR White resin combined with en bloc staining techniques for large specimens with thick and numerous spicules, but paraffin embedding and subsequent staining for whole small specimens. For FISH on siliceous sponges, we recommend Histocryl embedding if the spicule content is high, but paraffin embedding if it is low. Classical histological techniques are used for detailed tissue examinations.     

Spicule records of <Emphasis Type="Italic">Ephydatia fluviatilis</Emphasis> as a proxy for hydrological and environmental changes in the shallow Lake Trasimeno (Umbria,Italy)

This research shows the results of an analysis of siliceous spicules found in sediment cores collected in Lake Trasimeno (Umbria, Italy), a shallow lake that experienced an important water level lowering during the last century. A morphological analysis of sedimentary sponge records revealed that the spicules accumulated in the lake sediments over the last 150 years are attributable to Ephydatia fluviatilis, the only sponge species found in the lake in recent years. The stratigraphic analysis of the cores showed that the abundance and size of the sponge spicules (megascleres) have remarkably decreased, suggesting that a significant depletion of the sponge fauna occurred, particularly during the first half of the twentieth century. A correlation analysis has identified morpho-hydrological and related variables (the theoretical fraction of lake surface subjected to resuspension and the amount of total suspended solids) as the most significant factors explaining the change in density of sponge spicules. Two ecological explanations of the sponge decline are proposed, based on the sensitivity of the sponge both to the availability of suitable hard substrata for colonization, and to the amount of wind-resuspended solids. One-ended sigmoid response curves were obtained by regression and corresponding transfer functions were derived, which allow the mean water depth of the lake and total suspended solids to be inferred from spicule density records. The results support the use of sponge spicules as a paleohydrological and paleoecological proxy, application of which appears particularly promising for shallow-water systems.     

Middle and Late Cambrian sponge spicules from Hunan, China

Abundant and well-preserved assemblages of disarticulated sponge spicules occur in Middle and Late Cambrian platform carbonates of western Hunan, China. Assemblages recovered from 11 stratigraphic horizons include calcisponges, demosponges, and hexactinellids. Hexactinellida, in particular, are both abundant and diverse in Upper Cambrian carbonates. Comparison with spicule assemblages from Australia indicates that many of these taxa have long stratigraphic ranges, limiting their use in correlation. The morphological diversity of these spicules exceeds that known for living siliceous sponges, supporting the observation that during the Cambrian radiation, sponges, like other metazoans, evolved a variety of architectural forms not observed in later periods. Like conodonts, individual sponges can produce more than one spicule form; thus, an "apparatus genus" concept based on multiple co-occurring elements may eventually prove useful in the biostratigraphic and paleobiological interpretation of disarticulated sponge spicules. Four distinctive forms are recognized as new taxa: Australispongia sinensis new genus and species, Flosculus gracilis new genus and species, Pinnatispongia bengtsoni new genus and species, and Nabaviella paibiensis new species.     

Calcification processes of siliceous sponges in Viséan Limestones (Counties Sligo and Leitrim,Northwestern Ireland)

Summary In the Lower Carboniferous limestones and shales of the Benbulben Range, Counties Sligo and Leitrim, northwestern Ireland, a suite of carbonate nodules, about 1 to 4 cm in diameter, has been sampled and investigated by thin sectioning. The nodules consist of micritic, peloidal and fenestral fabrics. Many of them contain relics of desma bearing demosponges and hexactinellid sponge skeletons. The nodules are interpreted as calcified siliceous sponges. Micrite and peloids have been formed via microbial activity during the decay of the soft sponge tissue. The actual processes are deduced from Recent examples investigated at Lizard Island, Autralia, byReitner (1993). The skeletal opal was dissolved very early. In places where the skeleton was already embedded in micrite the spicules are preserved as molds cemented by granular ferroan calcite. The nodules were extensively inhabited by agglutinating polychaetes and bored by sponges. Micrite clasts have been exported to the surrounding seafloor before the sponges were completely covered by sediments. Fenestral fabrics represent primary sponge cavities, that may be enlarged due to volume reduction of the soft tissue during calcification. Some originated from non-calcification of decaying tissue. The granular calcite cement, filling the fenestral fabrics, contains relics of spicules and faintly visible peloids floating unsupportedly in the cement. These peloids were probably produced in situ by calcification of organic mucilages that filled the cavities almost entirely. It is evident that most diagenetic processes occurring within the sponges happened on the seafloor, most likely within the still living individuals. Possibly the nodules represent a precursor stage of mud mound development.     

Intra-epithelial spicules in a homosclerophorid sponge

Attempts to understand the intricacies of biosilicification in sponges are hampered by difficulties in isolating and culturing their sclerocytes, which are specialized cells that wander at low density within the sponge body, and which are considered as being solely responsible for the secretion of siliceous skeletal structures (spicules). By investigating the homosclerophorid Corticium candelabrum, traditionally included in the class Demospongiae, we show that two abundant cell types of the epithelia (pinacocytes), in addition to sclerocytes, contain spicules intracellularly. The small size of these intracellular spicules, together with the ultrastructure of their silica layers, indicates that their silicification is unfinished and supports the idea that they are produced "in situ" by the epithelial cells rather than being incorporated from the intercellular mesohyl. The origin of small spicules that also occur (though rarely) within the nucleus of sclerocytes and the cytoplasm of choanocytes is more uncertain. Not only the location, but also the structure of spicules are unconventional in this sponge. Cross-sectioned spicules show a subcircular axial filament externally enveloped by a silica layer, followed by two concentric extra-axial organic layers, each being in turn surrounded by a silica ring. We interpret this structural pattern as the result of a distinctive three-step process, consisting of an initial (axial) silicification wave around the axial filament and two subsequent (extra-axial) silicification waves. These findings indicate that the cellular mechanisms of spicule production vary across sponges and reveal the need for a careful re-examination of the hitherto monophyletic state attributed to biosilicification within the phylum Porifera.     

Silicatein expression in the hexactinellid Crateromorpha meyeri: the lead marker gene restricted to siliceous sponges

The siliceous spicules of sponges (Porifera) are synthesized by the enzyme silicatein. This protein and its gene have been identified so far in the Demospongiae, e.g., Tethya aurantium and Suberites domuncula. In the Hexactinellida, the second class of siliceous sponges, the mechanism of synthesis of the largest bio-silica structures on Earth remains obscure. Here, we describe the morphology of the spicules (diactines and stauractines) of the hexactinellid Crateromorpha meyeri. These spicules are composed of silica lamellae concentrically arranged around a central axial canal and contain proteinaceous sheaths (within the siliceous mantel) and proteinaceous axial filaments (within the axial canal). The major protein in the spicules is a 24-kDa protein that strongly reacts with anti-silicatein antibodies in Western blots. Its cDNA has been successfully cloned; the deduced hexactinellid silicatein comprises, in addition to the characteristic catalytic triad amino acids Ser-His-Asn and the "conventional" serine cluster, a "hexactinellid C. meyeri-specific" Ser cluster. We show that anti-silicatein antibodies react specifically with the proteinaceous matrix of the C. meyeri spicules. The characterization of silicatein at the genetic level should contribute to an understanding of the molecular/biochemical mechanism of spiculogenesis in Hexactinellida. These data also indicate that silicatein is an autapomorphic molecule common to both classes of siliceous sponges.     

Trophic ecology of a freshwater sponge (Spongilla lacustris) revealed by stable isotope analysis

The vital roles that sponges play in marine habitats are well-known. However, sponges inhabiting freshwaters have been largely ignored despite having widespread distributions and often high local abundances. We used natural abundance stable isotope signatures of carbon and nitrogen (δ ¹³C and δ ¹⁵N) to infer the primary food source of the cosmopolitan freshwater sponge Spongilla lacustris. Our results suggest that S. lacustris feed largely on pelagic resources and may therefore link pelagic and benthic food webs. A facultative association between S. lacustris and endosymbiotic green algae caused S. lacustris to have significantly depleted carbon and nitrogen signatures that may reflect carbon and nitrogen exchange between sponges and their symbiotic algae. Isotopic data from specialist sponge consumers demonstrated that sponges hosting zoochlorellae were the major component of the diet of the spongillafly Climacia areolaris and the sponge-eating caddisfly Ceraclea resurgens suggesting that the symbiosis between freshwater sponges and algae is important to sponge predator trophic ecology. Our results help define the role of sponges in freshwater ecosystems and shed new light on the evolution and ecological consequences of a complex tri-trophic symbiosis involving freshwater sponges, zoochlorellae, and spongivorous insects.     

深海六放海绵大骨针的结构与特性

在海绵动物(多孔动物)中,六放海绵和寻常海绵为硅质骨骼.生活在深海(1 000 m)中的六放海绵是最古老的海绵动物,其中间单根海绵和春氏单根海绵有长达3 m的骨针,是地球上最长的生物硅结构.利用电子显微技术观测, 这些直径达8 mm的巨大根须骨针具有同心层状结构,其横截面显示明显的构造分界:中间为含有轴丝的轴管,外围是一50-150 μm厚的轴筒,最外面为区状区(300-500层,每层厚度3-5 μm).生物化学研究显示其主要的蛋白质为35 kD大分子,另外,还检测到23-24 kD 多肽,可能是硅蛋白相关蛋白.依据现有的红血球凝聚活性,从骨针提取物中也检测到了凝集素.由电子探针获得其化学成分主要为Si,K和Na.此外,骨针的光传输实验表明,该巨大根须骨针用作光纤可传输600 nm至1 400 nm范围的光,而滤掉小于600 nm的光(类似高通滤波器)和大于1 400 nm 的红外光(类似低通滤波器).另外,从六放海绵的空囊泡沫海绵中分离出一个基因并确证了其推导的编码蛋白序列,该蛋白编码一个光裂合酶相关蛋白,蛋白相似性比较结果显示属于光裂合酶相关蛋白中多细胞动物隐色素一类.基于以上数据给出了六放海绵硅质骨针形成的示意图.另外,由单根海绵骨针可作为波导传输光/电和/或化学信号,推断在海绵动物中有类似神经系统的网络系统[动物学报 53(3):557-569,2007].     

Does the skeleton of a sponge provide a defense against predatory reef fish?

Sponge tissue often contains two structural components in high concentrations: spicules of silica, and refractory fibers of protein (spongin). Some terrestrial plants contain analogous structures, siliceous inclusions and refractory lignins, that have been demonstrated to deter herbivory. We performed feeding experiments with predatory reef fish to assess the deterrent properties of the structural components of three common Caribbean demosponges, Agelas clathrodes, Ectyoplasia ferox, and Xestospongia muta. The concentrations of spicules and spongin in the tissues varied widely between the three species, but when assayed at their natural volumetric concentrations, neither spicules (all three species assayed) nor the intact spiculated spongin skeleton (A. clathrodes and X. muta assayed) deterred feeding by reef fish in aquarium or field assays using prepared foods of a nutritional quality similar to, or higher than, that of sponge tissue. Spicules deterred feeding in aquarium assays when incorporated into prepared foods of a nutritional quality lower than that of sponge tissue (15–19 times less protein), but spiculated spongin skeleton was still palatable, even in prepared foods devoid of measurable protein, and even though spicules embedded in spongin were oriented in their natural conformation. Based on comparisons of the nutritional qualities of the tissues of the three sponge species and of the prepared foods, sponge tissue would have to be much lower in food value (5 times less protein or lower) for spicules to provide an effective defense, and spicules in combination with the spongin skeleton would be unlikely to provide an effective defense regardless of the nutritional quality of the tissue. Unlike terrestrial plants, marine sponges may use silica and refractory fibers solely for structural purposes.     

Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China

Botting, J.P., Muir, L.A., Xiao, S., Li, X. & Lin, J.‐P. 2012: Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. from the Early Cambrian of South China. Lethaia, Vol. 45, pp. 463–475. The relationships of the extant sponge classes, and the nature of the last common ancestor of all sponges, are currently unclear. Early sponges preserved in the fossil record differ greatly from extant taxa, and therefore information from the fossil record is critical for testing hypotheses of sponge phylogenetic relationships that are based on modern taxa. New specimens of the enigmatic sponge Lenica sp., from the Early Cambrian Hetang Biota of South China, exhibit an unusual spicule structure. Each spicule consists of a siliceous core with an axial canal, an organic outer layer and a middle layer interpreted to have been originally calcium carbonate. This finding confirms previous work suggesting the existence of biminerallic spicules in early sponges. Combined with data from other early sponges, the new findings imply that the two fundamental spicule structures of modern sponges were derived from a compound, biminerallic precursor. Spicules are therefore homologous structures in Calcarea and Silicea, and if sponges are paraphyletic with respect to Eumetazoa, then spicules may also have been a primitive feature of Metazoa. □Calcarea, Early Cambrian, Hetang Biota, phylogeny, Silicea, taphonomy.     

Hierarchical assembly of the siliceous skeletal lattice of the hexactinellid sponge Euplectella aspergillum

Despite its inherent mechanical fragility, silica is widely used as a skeletal material in a great diversity of organisms ranging from diatoms and radiolaria to sponges and higher plants. In addition to their micro- and nanoscale structural regularity, many of these hard tissues form complex hierarchically ordered composites. One such example is found in the siliceous skeletal system of the Western Pacific hexactinellid sponge, Euplectella aspergillum. In this species, the skeleton comprises an elaborate cylindrical lattice-like structure with at least six hierarchical levels spanning the length scale from nanometers to centimeters. The basic building blocks are laminated skeletal elements (spicules) that consist of a central proteinaceous axial filament surrounded by alternating concentric domains of consolidated silica nanoparticles and organic interlayers. Two intersecting grids of non-planar cruciform spicules define a locally quadrate, globally cylindrical skeletal lattice that provides the framework onto which other skeletal constituents are deposited. The grids are supported by bundles of spicules that form vertical, horizontal and diagonally ordered struts. The overall cylindrical lattice is capped at its upper end by a terminal sieve plate and rooted into the sea floor at its base by a flexible cluster of barbed fibrillar anchor spicules. External diagonally oriented spiral ridges that extend perpendicular to the surface further strengthen the lattice. A secondarily deposited laminated silica matrix that cements the structure together additionally reinforces the resulting skeletal mass. The mechanical consequences of each of these various levels of structural complexity are discussed.     

Metamorphosis of coeloblastula performed by multipotential larval flagellated cells in the calcareous sponge Leucosolenia laxa

The calcareous sponge Leucosolenia laxa releases free-swimming hollow larvae called coeloblastulae that are the characteristic larvae of the subclass Calcinea. Although the coeloblastula is a major type of sponge larva, our knowledge about its development is scanty. Detailed electron microscopic studies on the metamorphosis of the coeloblastula revealed that the larva consists of four types of cells: flagellated cells, bottle cells, vesicular cells, and free cells in a central cavity. The flagellated cells, the principal cell type of the larva, are arranged in a pseudostratified layer around a large central cavity. The larval flagellated cells characteristically have glutinous granules that are used as internal markers during metamorphosis. After a free-swimming period the larva settles on the substratum, and settlement apparently triggers the initiation of metamorphosis. The larval flagellated cells soon lose their flagellum and begin the process of dedifferentiation. Then the larva becomes a mass of dedifferentiated cells in which many autophagosomes are found. Within 18 h after settlement, the cells at the surface of the cell mass differentiate to pinacocytes. The cells beneath the pinacoderm differentiate to scleroblasts that form triradiate spicules. Finally, the cells of the inner cell mass differentiate to choanocytes and are arranged in a choanoderm that surrounds a newly formed large gastral cavity. We found glutinous granules in these three principal cell types of juvenile sponges, thus indicating the multipotency of the flagellated cells of the coeloblastula.     

A synthetic biology approach for the fabrication of functional (fluorescent magnetic) bioorganic–inorganic hybrid materials in sponge primmorphs

During evolution, sponges (Porifera) have honed the genetic toolbox and biosynthetic mechanisms for the fabrication of siliceous skeletal components (spicules). Spicules carry a protein scaffold embedded within biogenic silica (biosilica) and feature an amazing range of optical, structural, and mechanical properties. Thus, it is tempting to explore the low-energy synthetic pathways of spiculogenesis for the fabrication of innovative hybrid materials. In this synthetic biology approach, the uptake of multifunctional nonbiogenic nanoparticles (fluorescent, superparamagnetic) by spicule-forming cells of bioreactor-cultivated sponge primmorphs provides access to spiculogenesis. The ingested nanoparticles were detected within intracellular vesicles resembling silicasomes (silica-rich cellular compartments) and as cytosolic clusters where they lent primmorphs fluorescent/magnetic properties. During spiculogenesis, the nanoparticles initially formed an incomplete layer around juvenile, intracellular spicules. In the mature, extracellular spicules the nanoparticles were densely arranged as a surface layer that rendered the resulting composite fluorescent and magnetic. By branching off the conventional route of solid-state materials synthesis under harsh conditions, a new pathway has been opened to a versatile platform that allows adding functionalities to growing spicules as templates in living cells, using nonbiogenic nanoscale building blocks with multiple functionalities. The magnet-assisted alignment renders this composite with its fluorescent/magnetic properties potentially suitable for application in biooptoelectronics and microelectronics (e.g., microscale on-chip waveguides for applications of optical detection and sensing).