Dynamic structure of the mesohyl in the sponge Chondrosia reniformis (Porifera, Demospongiae)

The common demosponge Chondrosia reniformis possesses the capacity to undergo an unusual creep process which results in the formation of long outgrowths from the parent body. These shape changes, which have been interpreted as adaptive strategies related to environmental factors, asexual reproduction or localised locomotor phenomena, are due mainly to the structural and mechanical adaptability of the collagenous mesohyl. This contribution describes the morphological correlates of mesohyl plasticisation in C. reniformis. The microscopic anatomy of the mesohyl was examined when it was in different physiological conditions: (1) standard ”resting” condition, (2) ”stiffened” condition and (3) dynamic ”creep” condition. In this last case four representative regions of the sponge body were analysed: the parent region, the elongation region, the transition region and the propagule region. The results show that the histological modification of the sponge mesohyl during plasticisation is limited and localised. The most significant structural changes involve mainly cytological features of specific cellular components characterised by granule inclusions (i.e. the spherulous cells) and the arrangement and density of the collagenous extracellular framework, though the integrity of the collagen fibrils themselves is not affected. Morphological and functional aspects of mesohyl plasticisation invite comparison with the mutable collagenous tissue of echinoderms. Possible functional analogies between these two tissues are hypothesised. Accepted: 29 June 2001     

Morphological and genetic differences in ecologically distinct populations of Petrosia (Porifera, Demospongiae)

The taxonomic status of two sponge tnorphotypes living sympatrically in Mediterranean caves and usually ascribed to Petrosia ficiformis was elucidated on the basis of morphological, morphometric and genetic features. The two morphotypes, spherical and cylindrical, showed differences in the shape and size of spicules and in the morphology of the aquiferous system. Electrophoretic analyses demonstrated that the two morphotypes are reproductively independent and so they should be considered as distinct biological species. The spicular features allow attribution of the cylindrical morphotype to P.ficiformis and the spherical one to P. clavata. For these two species parasympatric speciation is proposed.     

The aquiferous system of two <Emphasis Type="Italic">Oceanapia</Emphasis> species (Porifera,Demospongiae) studied by corrosion casts

The aquiferous systems of two Indopacific Oceanapia species (Oceanapiidae) were studied by corrosion casts: O. amboinensis living in shallow lagoons and O. fistulosa living at the base of the reef slope. Both species show a massive, entirely buried body, emerging from the sediment only by long, completely close fistules. Particularly in O. fistulosa the corrosion casts revealed a complex, grape-like structure of the choanosome organised in anatomical and functional units composed by an incurrent web whose anastomosed meshes are crossed by a central excurrent canal. A system of thin canals connects the two systems giving rise to an area of choanocyte chambers. The corrosion casts revealed that in both species incurrent water penetrates into the sponge body by the fistules and that it is expelled through specialised structures buried in the sediment. This observation is in accordance with field experiments performed on O. fistulosa. In some specimens of this species, a solution of china ink injected into plastic bags enveloping the external fistules was observed, after waiting for a while, to flow through the buried structures.     

The spermatogenesis ofHalichondria panicea (Porifera,Demospongiae)

Summary Spermatogenesis of the marine spongeHalichondria panicea begins with the break up of choanocyte chambers, choanocytes constituting the origin of spermatogonia. The transition from choanocytes to spermatogonia is direct, without cell division. Already the spermatogonia are flagellated. The ensuing large aggregates of spermatogonia are enclosed by spermatocyst-building cells. Further development takes place within the spermatocysts, mostly arranged in fields which, however, lack any developmental gradient. Within a single spermatocyst development is mostly synchronous. Spermatogonia transform into first order spermatocytes directly. The transition from spermatid to spermatozoon is characterized by an unusual prolongation of the chromatin, often resulting in a helical form of the chromosome material and a strong enlargement of the mitochondria which align with the nucleus, leading to an irregular shape of the spermatozoon. Another exceptional feature is the virtual absence of a Golgi apparatus during all stages of spermatogenesis. TheH. panicea investigated here contained only male reproductive elements, thus appear to be gonochorists. Some features of the spermatogenesis ofH. panicea, such as dissolving choanocyte chambers, the enclosure of spermatogonia by spermatocyst-building cells and the formation of a synaptonemal complex in first order spermatocytes occur in other sponge species as well; however, the early presence of flagella in spermatogonia, the absence of the Golgi apparatus and the later irregular development of nuclei, mitochondria and the spermatozoa themselves represent features hitherto not observed in sponges.     

Larval development in the Homoscleromorpha (Porifera, Demospongiae)

Abstract. Embryonic development from coeloblastula to fully developed larva was investigated in 8 Mediterranean homoscleromorph species: Oscarella lobularis, O. tuberculata, O. microlobata, O. imperialis, Plakina trilopha, P. jani, Corticium candelabrum , and Pseudocorticium jarrei. Morphogenesis of the larva is similar in all these species; however, cell proliferation is more active in species of Oscarella than in Plakina and C. candelabrum. The result of cell division is a wrinkled, flagellated larva, called a cinctoblastula. It is composed of a columnar epithelium of polarized, monoflagellated cells among which are scattered a few non-flagellated ovoid cells. The central cavity always contains symbiotic bacteria. Maternal cells are also present in O. lobularis, O. imperialis , and P. jarrei. In the fully developed larva, cell shape and dimensions are constant for each species. The cells of the anterior pole have large vacuoles with heterogeneous material; those of the postero-lateral zone have an intranuclear paracrystalline inclusion; and the flagellated cells of the posterior pole have large osmiophilic inclusions. Intercellular junctions join the apical parts of the cells, beneath which are other specialized cell junctions. A basement membrane underlying the flagellated cells lines the larval cavity. This is the first observation of a basement membrane in a poriferan larva. The basal apparatus of flagellated cells is characterized by an accessory centriole located exactly beneath the basal body. The single basal rootlet is cross striated. The presence of a basement membrane and a true epithelium in the larva of Homoscleromorpha—unique among poriferan clades and shared with Eumetazoa—suggests that Demospongiae could be paraphyletic.     

The aquiferous system of<Emphasis Type="Italic"> Scolymastra joubini</Emphasis> (Porifera,Hexactinellida) studied by corrosion casts

The aquiferous system of the hexactinellid sponge Scolymastra joubini was studied by corrosion casts in specimens from 30 m depth in Terra Nova Bay (Ross Sea, Antarctica). The aquiferous system of hexactinellids is traditionally considered different from that of Demospongiae, lacking a true canal organisation, with water percolating through a trabecular net. The corrosion cast analysis provided evidence that the aquiferous system of S. joubini is characterised by the presence of a system of vessels and not simple spaces or lacunas inside the trabecular net. These vessels constitute incurrent and excurrent ramified structures modularly repeated, respectively, on the external and internal surfaces. This evidence strongly confirms, on a morphological basis, the idea of a unidirectional water flow in Hexactinellida and must be taken into consideration in the study of the phylogenetic relationships between different higher taxa of the Porifera.     

In vitro sponge fragment culture of Chondrosia reniformis (Nardo, 1847)

In vitro cultivation systems for sponges (Porifera) have to be developed to produce compounds of value in biotechnological processes. Organotypic culture attempts, which maintain or mimic the natural tissue structure, are promising ways towards a biotechnology of sponges. We used the Mediterranean species Chondrosia reniformis for sponge fragment in vitro cultivation. The species is common throughout the Mediterranean, easy to keep in aquariums and shows good recovery and regeneration after fragmentation. The regeneration process of the 50-80 mm(3) fragments lasted for several days and resulted in a rounded or ovoid body shape. The aquiferous system was reduced. Cells performed proliferation during the first weeks as we could demonstrate by 5-bromo-2'-deoxy-uridine (BrdU) incorporation. No proliferation could be demonstrated after a culture period of 3 months, but silicate uptake. Cellular density decreased with cultivation length, but collagen production increased. Fragments have been kept in culture up to 19 months. C. reniformis can be used as a model system to develop feeding strategies and evaluate the biotechnological potential of sponge fragment in vitro cultivation.     

Microcirculation in mouse spleen (nonsinusal) studied by means of corrosion casts

Corrosion casts of mouse spleen, examined by scanning electron microscopy, enabled vascular pathways of the arterial, intermediate, and venous circulations to be traced over considerable distances. The arterial tree is surrounded by white pulp immediately upon entering at the hilus, and relatively few arterioles extend into red pulp. A profusion of capillaries is present in both periarterial lymphatic sheaths and lymphatic nodules, arranged as bifurcating systems (rather than anastomosing networks) terminating in the marginal sinus (MS) and marginal zone (MZ). The MS, which is situated between white pulp and MZ, consists of a discontinuous layer of flattened anastomosing spaces which are up to six times as large as those in rat spleen. Extensive filling of the entire MZ took place before appreciable filling of surrounding red pulp occurred. Capillary terminations in red pulp are always continuous with reticular meshwork, i.e., no evidence for a “closed” circulation was found. Casts of the venous origins support the classification “pulp venules” rather than “venous sinuses” and show major morphological differences from the richly anastomosing system of sinuses in rat. In the subcapsular region of mouse spleen large anastomosing veins ramify over the surface, with reticular meshwork occupying extensive areas between adjacent veins. For in vivo microscopy this arrangement offers advantages over that found in rat spleen (accompanying paper), where almost the entire surface is densely covered with venous sinuses.     

Taxonomic revision of the Mediterranean Plakina Schulze (Porifera, Demospongiae, Homoscleromorpha)

Only three species of the sponge genus Plakina Schulze have been described from the Mediterranean since 1880, in spite of a large amount of allegedly intraspecific variability in morphological characters. However, recent genetic studies based on electrophoretic techniques have revealed extensive cryptic speciation in north-western Mediterranean Plakina , demonstrating that most of this variation was interspecific rather than intraspecific. We describe in detail the morphology and anatomy of four new species of Plakina from the Mediterranean– P. crypta, P. weinbergi, P. endoumensis and P. jani –of which the latter two were discovered through allozyme electrophoresis. Plakina monolopha Schulze and P. trilopha Schulze are redescribed, and their morphological and geographical limits are discussed along with those of P. dilopha Schulze. Accurate analysis of the internal anatomy and of the shape and ramification pattern of lophose spicules in scanning electron microscopy provides new, powerful morphological criteria for species discrimination in Plakina. More widespread use of such new taxonomic characters should provide evidence against the alleged cosmopolitanism of some Plakina species, thus generating an increase in estimates of the biodiversity of plakinids.     

Petrosia ficiformis (Poiret, 1789): an excellent model for holobiont and biotechnological studies

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The aggregation of prokaryotic and eukaryotic cells has resulted in evolution of organisms with remarkable abilities to synthetize natural bioactive compounds of biotechnological relevance. Marine sponges such as Petrosia ficiformis are examples of this evolutionary strategy. The P. ficiformis microbiome, which produces a diversity of chemical compounds, plays a fundamental role in this sponge’s extraordinary adaptation to various ecological conditions. The microbial community of P. ficiformis seems representative of sponge microbiomes, but it has an unusual exclusively horizontal transmission. This uncommon feature, together with its wide environmental distribution, its ability to generate 3D cell cultures that host symbionts, and the availability of meta-omics and physiology information make this sponge an effective model to study the complexity of holobionts.     

Ultrastructural study of spermatogenesis in Oscarella lobularis (Porifera,Demospongiae)

Summary

The various phases of spermatogenesis in the demosponge Oscarella lobularis were studied by electron microscopy. Spermatogenesis occurs within spermatic cysts, which are presumed to derive from choanocyte chambers by transformation of choanocytes into spermatogonia. Germ cells develop asynchronously within spermatocysts, and cytoplasmic bridges, indicating incomplete cells division, connect several germ cells. Attached spermatogonia suggest gonial generations. Spermatocytes I typically show the presence of synaptonemal complexes indicating meiotic divisions. Spermatocytes II have a small size probably because of the meiotic divisions of spermatocytes I. Spermatids are characterized by an acrosome, a big mitochondrion and a peripheral sheath of condensed chromatin surrounding a clearer central area in the nucleus. The mature spermatozoon shows a lateral flagellum and a flattened acrosome capping the nucleus. The phylogenetic implications of some features of the spermatozoon are suggested.     

Association of the sponge Tethya orphei (Porifera, Demospongiae) with filamentous cyanobacteria

Abstract. Specimens of the sponge Tethya orphei , collected in February 2005 on the underside of coral stones on Arì Athol (Maldives), have been processed for histological and ultrastructural investigations. The cortical layer of the sponge was found to be permeated by filamentous cyanobacteria, the trichomes of which measured 45–63 μm on average and were composed of 10–14 cells. The fine organization of the filaments was consistent with their taxonomic identification as Oscillatoria spongeliae. These filaments filled the cortical region of the sponge and penetrated inward into the upper choanosomal region, where they sometimes overlapped the siliceous spicule bundles. A budding specimen of T. orphei showed that the filaments were also present in the single bud protruding from the sponge surface, demonstrating that asexual reproduction can vertically transmit these symbionts from sponge to sponge. The occurrence of filaments in all the specimens studied is consistent with the assumption that filamentous cyanobacteria are not mere intruders but mutualistic symbionts with members of T. orphei.     

Post-larval development of the commercial sponge Spongia officinalis L. (Porifera, Demospongiae)

This study investigated the development of the larvae of Spongia officinalis in experimental conditions, after settlement on plastic substrates, using electron and light microscopy. The released larvae show a dark pigmented ring distinguishes the posterior larval pole. The youngest larvae, covered with a flagellate epithelium, move onwards by rotating on their longitudinal axis. Over time a creeping-like motion prevails, probably linked to the need for settlement. After a free-swimming period of 24-48 h, larvae settle on the artificial substrate by the anterior pole. At settlement, the flagellate epithelium is substituted by flattened cells, which delimit the outermost surface. Post-larvae were reared to about three months. The early phase of post-larval differentiation shows a solid interior mainly consisting of granular cells varying in shape and size. They are included in a dense collagen matrix that contains a conspicuous amount of bacteria. Lacunae are already evident in the initial phase of metamorphosis. In several of them, cell debris and nucleate cells are visible. This feature is consistent with a progressive reduction of the cell mass (autolysis). Neither choanocyte chambers nor canals differentiate. The morphogenetic process leads to a metamorph only consisting of vacuolated cells and collagen fibrils included in a thin fibrous coat.     

Molecular phylogenies challenge the classification of Polymastiidae (Porifera,Demospongiae) based on morphology

Polymastiidae Gray, 1867 is a worldwide distributed sponge family, which has a great significance for understanding of the demosponge deep phylogeny since the former order Hadromerida Topsent, 1894 has been recently split based on the molecular evidence and a new separate order has been established for the polymastiids. However, molecular data obtained from Polymastiidae so far are scarce, while the phylogenetic reconstruction based on morphology has faced a deficit of characters along with the vagueness of their states. The present study is a phylogenetic reconstruction of Polymastiidae based on novel data on two molecular markers, cytochrome oxidase subunit I and large subunit ribosomal DNA, obtained from a broad set of species. Monophyly of the family and nonmonophyly of four polymastiid genera are revealed, suggesting a high level of homoplasy of morphological characters, which are therefore not an appropriate base for the natural classification of Polymastiidae. Although the presented phylogenies cannot yet provide an alternative classification scheme, several strongly supported clades, which may be used as reference points in future classification, are recovered and three taxonomic actions are proposed: transfer of one species from Radiella to Polymastia Bowerbank, 1862; transfer of three species from Radiella Schmidt, 1870 to Spinularia Gray, 1867; and the consequent abandonment of Radiella.     

Microcirculation of the rat omentum studied by means of corrosion casts

A study of the microvasculature of the omentum using corrosion casts was undertaken. The object was to supply information regarding the morphology of the three-dimensional structure of the microvasculature, information which may be valuable in understanding the functions of the omentum. Corrosion casts of rat omenta were prepared and studied. Characteristic glomerular-like capillary beds were identified. Some of these beds were densely and others loosely arranged. Two types of capillaries made up these beds, tortuous and straight capillaries. These beds also showed a planate surface giving the impression that they lie directly under the mesothelium.     

Epibiontic and endobiontic polychaetes of Geodia cydonium (Porifera,Demospongiae) from the Mediterranean Sea

Polychaete assemblages associated to the sponge Geodia cydonium were investigated at two sampling sites in the Mediterranean Sea: Porto Cesareo Basin (Apulia) and Marsala Lagoon (Sicily), both characterized by sheltered hydrodynamic conditions. Samples were seasonally performed during 1997, in order to compare the assemblages coming from the two localities studied, considering separately the internal and external tissues of the sponge, and with the aim of evaluating the influence of sponge size on polychaete colonization. The examined sponge is characterized by a peculiar stratification of its tissues: an external thick and hard layer, the cortex, and an internal softer one, the choanosome. Statistical analysis showed that this was the main factor controlling polychaete assemblage, with the internal tissue, less rich and diversified, appearing impoverished with respect to the external layer. A similarity in species composition was observed between sites, even though some differences were evidenced in the abundance of some species, mainly reflecting differences in local environmental conditions. Species richness and density increased with the increasing sponge size. Such a situation is particularly evident at Porto Cesareo, where sponges are covered by an algal layer which is particularly rich on the largest specimens, thus suggesting that most of the species of polychaetes were linked more to the neighbouring environment than to the sponge itself.     

Investigation of the budding process in Tethya citrina and Tethya aurantium (Porifera, Demospongiae)

The budding process has been studied in two congeneric Mediterranean species belonging to Tethya from different sampling sites: Marsala and Venice Lagoons (Tethya citrina); Marsala Lagoon and Porto Cesareo Basin (Tethya aurantium). Buds, connected to the adult by a spiculated stalk, differ between the two species in morphology and size, since those of T. citrina are small with elongated bodies, showing only a few spicules protruding from the apical region, whereas those of T. aurantium are round, larger, and show spicules radiating from the peripheral border. In T. citrina, cells with inclusions, varying in electron density and size, represent the main cell types of the buds. In T. aurantium, the cell component shows a major diversification, resulting from spherulous cells, grey cells, vacuolar cells and peculiar micro-vesicle cells. Neither canals nor choanocyte chambers were observed in the buds of the two species. In T. citrina, bud production is similar in both sampling sites. In T. aurantium, budding occurs more rarely in Porto Cesareo Basin, probably in relation with environmental factors, such as the covering of the cortex by sediment and micro-algae. Finally, in the buds of both species, the spicule size does not differ from that of the cortex of the adult sponges, further supporting the main involvement of the cortex in organizing the skeletal architecture of the buds.     

The vacuolar cells of Oscarella lobularis (Porifera,Demospongiae): Ulatrastructural organization,origin, and function

This work is concerned with the ultrastructural organization and some histochemical features of the vacuolar cells of the demosponge Oscarella lobularis. Vacuolar cells are characterized by large clear vacuoles containing an aqueous fluid. They are commonly found in the mesohyl of this sponge and tend to constitute a sort of parenchyma in the choanosome. Mobile cells of the mesohyl appear to differetiate into vacuolar cells through the progressive formation of wide cytoplasmic lacunae. We have identified four types of cells showing progressive transformation toward the vacuolar cell type. Precursors (types 1–4) of the vacuolar cells probably derive from endopinacocytes, since they share several histochemical and ultrastructural characteristics with them. Our data support the notion that vacuolar cells are involved in the synthesis of collagen, act as a mechanical support of the sponge body, and are eventually extruded from the sponge through the canals of the aquiferous system.     

Silica spicules and axial filaments of the marine sponge Stelletta grubii (Porifera,Demospongiae)

Summary In all cases an organic axial filament within the silica spicules of Stelletta grubii forms the core of the major axes of the glass. In the small, star-shaped silica spicules (asters) the filament is shown for the first time to be radial with an enlarged center; in the large four-rayed spicules (triaenes) it is four-rayed; and in the large single-rayed spicules (oxeas) the filament is single-rayed. In situ, the filament is not dissolved by boiling nitric acid and thus is apparently protected by encasement within the glass which can also be stratified. The small silica asters are formed by single cells which resemble the so-called spherulous cells of other sponges. The very large size of triaenes and oxeas suggests that they may possibly be formed by more than one cell. The diameter of the filament in the much smaller asters is much narrower than the filament in the larger spicules, indicating a possible relationship between filament diameter and spicule diameter. While the axial filament in larger spicules frequently has a triangular cross-section it can also be hexaognal. Some aster filaments also retain a close to hexagonal cross-section. Filaments freed from large spicules by hydrofluoric acid display a complex morphology; possibly there is an internal silicified core. Some reported aspects of filament morphology are, however, probably artefacts of desilicification with hydrofluoric acid. Offprint requests to: T.L. Simpson, Department of Biology, University of Hartford, West Harford, Connecticut 06117, USA (Permanent affiliation)