Sponges (Porifera) and Sponge Microbes
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SPONGES (PORIFERA) AND SPONGE MICROBES
Silica Biomineralization, Sponges Sinter Stromatolites Sulfate-Reducing Bacteria
SPONGES (PORIFERA) AND SPONGE MICROBES Friederike Hoffmann1, Marie-Lise Schläppy2 Sars International Centre for Marine Molecular Biology, Bergen, Norway 2 Max Planck Institute for Marine Microbiology, Bremen, Germany
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Synonyms Sponge-associated bacteria; Sponge-associated microbes; Sponge-associated microbiota; Sponge bacteria; Sponge– microbe systems; Sponge symbionts Definition Sponges are sessile multicellular aquatic animals (Lat. Porifera = bearing pores) whose bodies have a typical body plan which allows water to pass through the animals. Sponges are characterized by a skeleton made of calcareous, siliceous spicules or horny fibers. Sponge microbes: Bacteria and archaea that live in close and permanent association with sponges, usually in the mesohyl between sponge cells. Introduction Sponges are sedentary benthic organisms found in shallow waters on tropical coral reefs to the Arctic and the deep sea. Some species, however, are restricted to freshwater ecosystems. Sponges are characterized by a typical body plan built around a system of water canals and chambers (Figure 1a). Within the chambers, flagellated cells called choanocytes produce a water current that enters the sponge body through surface pores (ostia) and leaves through larger openings called oscula. Hence, sponges are filter feeders and incorporate particles from the water as energy and nutrient source. An external cell layer (pinacoderm) encloses the sponge mesohyl, a glycosidic matrix containing several cell types which perform a variety of functions. Sponge cells show a low degree of specialization and a high degree of independence so that the sponge body in some respect resembles a protozoan colony. However, sponges are, without any doubt, placed as true members of the Metazoan (Ax, 1995; Müller, 1998a, b). Sponges have been grouped into three classes: Calcarea, Hexactinellida, and Demospongiae. Calcarea are characterized by the presence of calcareous spicules. The upgrade of this class to the phylum level has recently been proposed by Borchiellini et al. (2001). Hexactinellida are characterized by siliceous spicules of hexactine structure and syncytial tissue organization.
Demospongiae, the most numerous and diverse class, is a nonmonophyletic group (Boury-Esnault, 2006). They generally have a mineral skeleton made of siliceous spicules, but several lineages, like the common bath sponge, have no mineral skeleton but a network of fibers instead. Modern sponge phylogeny is now based on a combination of molecular methods and sponge morphological features, but sponge spicules are still important features for species determination and identification of sponges in the fossil record. Sponges form one of the deepest radiations of the Metazoa and can be regarded as one of the oldest animal phylum still alive. The spicule record for sponges starts in the late Proterozoic (Reitner and Wörheide, 2002), while chemofossil records e
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