Molecular systematics of sponges (Porifera)

The first application of molecular systematics to sponges was in the 1980s, using allozyme divergence to dis-criminate between conspecific and congeneric sponge populations. Since this time, a fairly large database has been accumulated and, although the first findings seemed to indicate that sponge species were genetically more divergent than those of other marine invertebrates, a recent review of the available dataset indicates that levels of interspecific gene identities in most sponges fall within the normal range found between species of other invertebrates. Nevertheless, some sponge genera have species that are extremely divergent from each other, suggesting a possible polyphyly of these genera. In the 1990s, molecular studies comparing sequences of ribosomal RNA have been used to reappraise the phylogenetic relationships among sponge genera, families, orders and classes. Both the 18S small subunit and the 28S large subunit rRNA genes have been sequenced (41 complete or partial and 75 partial sequences, respectively). Sequences of 18S rRNA show good support for Porifera being true Metazoa, but they are not informative for resolving relationships among genera, families or orders. 28S rRNA domains D1 and D2 appear to be more informative for the terminal nodes and provide resolution for internal topologies in sufficiently closely related species, but the deep nodes between orders or classes cannot be resolved using this molecule. Recently, a more conserved gene, Hsp70, has been used to try to resolve the relationships in the deep nodes. Metazoan monophyly is very well supported. Nevertheless, the divergence between the three classes of Porifera, as well as the divergence between Porifera, Cnidaria and Ctenophora, is not resolved. Research is in progress using other genes such as those of the homeodomain, the tyrosine kinase domain, and those coding for the aggregation factor. For the moment the dataset for these genes is too restricted to resolve the phylogenetic relationships of these phyla. However, whichever the genes, the phylogenies obtained suggest that Porifera could be paraphyletic and that the phylogenetic relationships of most of the families and orders of the Demospongiae have to be reassessed. The Calcarea and Hexactinellida are still to be studied at the molecular level.     

First report on chitinous holdfast in sponges (Porifera)

A holdfast is a root- or basal plate-like structure of principal importance that anchors aquatic sessile organisms, including sponges, to hard substrates. There is to date little information about the nature and origin of sponges’ holdfasts in both marine and freshwater environments. This work, to our knowledge, demonstrates for the first time that chitin is an important structural component within holdfasts of the endemic freshwater demosponge Lubomirskia baicalensis. Using a variety of techniques (near-edge X-ray absorption fine structure, Raman, electrospray ionization mas spectrometry, Morgan–Elson assay and Calcofluor White staining), we show that chitin from the sponge holdfast is much closer to α-chitin than to β-chitin. Most of the three-dimensional fibrous skeleton of this sponge consists of spicule-containing proteinaceous spongin. Intriguingly, the chitinous holdfast is not spongin-based, and is ontogenetically the oldest part of the sponge body. Sequencing revealed the presence of four previously undescribed genes encoding chitin synthases in the L. baicalensis sponge. This discovery of chitin within freshwater sponge holdfasts highlights the novel and specific functions of this biopolymer within these ancient sessile invertebrates.     

First evidence of miniature transposable elements in sponges (Porifera)

Transposable elements play a vital role in genome evolution and may have been important for the formation of the early metazoan genome, but only little is known about transposons at this interface between unicellular opisthokonts and Metazoa. Here, we describe the first miniature transposable elements (MITEs, Queen1 and Queen2) in sponges. Queen1 and Queen2 are probably derived from Tc1/mariner-like MITE families and are represented in more than 3,800 and 1,700 copies, respectively, in the Amphimedon queenslandica genome. Queen elements are located in intergenic regions as well as in introns, providing the potential to induce new splicing sites and termination signals in the genes. Further possible impacts of MITEs on the evolution of the metazoan genome are discussed.     

Condensation rhythm of fresh-water sponges (Spongillidae, Porifera)

The mesenchyme continuum of spongillids exhibits rhythmic changes that at first glance appear to be contractions. Actually, however, the process is a condensation initiated by the formation of punctate cell contacts and a rapid swelling of all mesenchymal cells. As the cells come into closer contact and the spaces between them are constricted, the volume of the mesenchyme shrinks, giving the impression of a contraction. It seems likely that rhythmic mesenchyme condensation assists the choanocyte chambers in pumping water through the sponge.     

The sterols of calcareous sponges (Calcarea, Porifera)

Sponges are sessile suspension-feeding organisms whose internal phylogenetic relationships are still the subject of intense debate. Sterols may have the potential to be used as independent markers to test phylogenetic hypotheses. Twenty representative specimens of calcareous sponges (class Calcarea, phylum Porifera) with a broad coverage within both subclasses Calcinea and Calcaronea were analysed for their sterol content. Two major pseudohomologous series were found, accompanied by some additional sterols. The first series encompassing conventional C(27) to C(29)Delta(5,7,22) sterols represented the major sterols, with ergosterol (ergosta-5,7,22-trien-3beta-ol, C(28)Delta(5,7,22)) being most prominent in many species. The second series consisted of unusual C(27) to C(29)Delta(5,7,9(11),22) sterols. Cholesterol occurred sporadically, mostly in trace amounts. The sterol patterns did not resolve intraclass phylogenetic relationships, namely the distinction between the subclasses, Calcinea and Calcaronea. This pointed towards major calcarean lipid traits being established prior to the separation of subclasses. Furthermore, calcarean sterol patterns clearly differ from those found in Hexactinellida, whereas partial overlap occurred with some Demospongiae. Hence, sterols only partly reflect the phylogenetic separation of Calcarea from both of the other poriferan classes that was proposed by recent molecular work and fatty acid analyses.     

Inferring the ancestral sexuality and reproductive condition in sponges (Porifera)

Considerable diversity abounds among sponges with respect to reproductive and developmental biology. Their ancestral sexual mode (gonochorism vs. hermaphroditism) and reproductive condition (oviparity vs. viviparity) however remain unclear, and these traits appear to have undergone correlated evolution in the phylum. To infer ancestral traits and investigate this putative correlation, we used DNA sequence data from two loci (18S ribosomal RNA and cytochrome c oxidase subunit I) to explore the phylogenetic relationships of 62 sponges whose reproductive traits have been previously documented. Although the inferred tree topologies, using the limited data available, favoured paraphyly of sponges, we also investigated ancestral character‐state reconstruction on a phylogeny with constrained sponge monophyly. Both parsimony‐ and likelihood‐based ancestral state reconstructions indicate that viviparity (brooding) was the likely reproductive mode of the ancestral sponge. Hermaphroditism is favoured over gonochorism as the sexual condition of the sponge ancestor under parsimony, but the reconstruction is ambiguous under likelihood, rendering the ancestry of sexuality unresolved in our study. These results are insensitive to the constraint of sponge monophyly when tracing the reproductive characters using parsimony methods. However, the maximum likelihood analysis of the monophyletic hypothetical tree rendered gonochorism as ancestral for the phylum. A test of trait correlation unambiguously favours the concerted evolution of sexuality and reproductive mode in sponges (hermaphroditism/viviparity, gonochorism/oviparity). Although testing ecological hypotheses for the pattern of sponge reproduction is beyond the scope of our analyses, we postulate that certain physiological constrains might be key causes for the correlation of reproductive characters.     

The fatty acids of calcareous sponges (Calcarea, Porifera)

Twenty-nine specimens of calcareous sponges (Class Calcarea, Phylum Porifera), covering thirteen representative species of the families Soleneiscidae, Leucaltidae, Levinellidae, Leucettidae, Clathrinidae, Sycettidae, Grantiidae, Jenkinidae, and Heteropiidae were analysed for their fatty acids. The fatty acids of Calcarea generally comprise saturated and monounsaturated linear (n-), and terminally methylated (iso-, anteiso-) C(14)-C(20) homologues. Furthermore, polyunsaturated C(22) fatty acids and the isoprenoic 4,8,12-trimethyltridecanoic acid were found. The most prominent compounds are n-C(16), iso-C(17), iso-C(18), n-C(18), n-C(20). In addition, a high abundance of the exotic 16-methyloctadecanoic acid (anteiso-C(19)) appears to be a characteristic trait of Calcarea. Long-chain 'demospongic acids', typically found in Demospongiae and Hexactinellida, are absent in Calcarea. The completely different strategy of calcarean fatty acid synthesis supports their phylogenetic distinctiveness from a common Demospongiae/Hexactinellida taxon. Both intraspecific and intraclass patterns of Calcarea showed great similarity, suggesting a conserved fatty acid composition that already existed in the last common ancestor of Calcinea and Calcaronea, i.e. before subclasses diverged.     

Canal systems and choanocyte chambers in freshwater sponges (Porifera,Spongillidae)

Summary The spongillid species Spongilla lacustris and Ephydatia fluviatilis possess choanocyte chambers of the classical eurypylous type. They are surrounded by the mesenchymal tissue and connected to the incurrent canal system by prosopyles and to the excurrent canal system by wide apopyles. Each apopyle is sealed against spaces between the basal choanocyte collar parts by a ring of uniflagellated cone cells. The functional aspects of the choanocyte chamber and canal structure are discussed.Dedicated to Prof. Dr. K.E. Wohlfarth-Bottermann, Bonn, in honor of his 65th birthday     

The stem cell concept in sponges (Porifera): Metazoan traits

Sponges are considered the oldest living animal group and provide important insights into the earliest evolutionary processes in the Metazoa. This paper reviews the evidence that sponge stem cells have essential roles in cellular specialization, embryogenesis and Bauplan formation. Data indicate that sponge archaeocytes not only represent germ cells but also totipotent stem cells. Marker genes have been identified which are expressed in totipotent stem cells and gemmule cells. Furthermore, genes are described for the three main cell lineages in sponge, which share a common origin from archaeocytes and result in the differentiation of skeletal, epithelial, and contractile cells.     

Glass sponges (Porifera, Hexactinellida) of the northern Mid-Atlantic Ridge

Glass sponges (Hexactinellida) collected under the framework of the MAR-ECO project on the G.O. Sars cruise to the northern Mid-Atlantic Ridge, between the Azores and the Reykjanes Ridge, and on the 49th cruise of Akademik Mstislav Keldysh to the Charlie-Gibbs Fracture Zone are described. Fourteen species were identified in the material. This relatively rich fauna includes several novel findings, indicating that the hexactinellid fauna of the northern Mid-Atlantic Ridge is poorly investigated. One genus, Dictyaulus, has never before been reported from the Atlantic Ocean. Two species belonging to the genera Heterotella and Amphidiscella are new to science. Two other species, Rossella nodastrella Topsent, 1915 and Doconestes sessilis Topsent, 1928, have been collected just one other time. Finally, a probable new genus of Euplectellidae, which unfortunately cannot be adequately described because of how small the specimens are, is represented among these collections. A large portion of dead, rigid skeletons of Euretidae and spicule mats of Rossellidae are also reported but not described in detail. Representation of some genera in the Charlie-Gibbs Fracture Zone, coupled with recent observations from elsewhere along the Mid-Atlantic mountain chain, suggests that this fauna is as similar to those of the Indian Ocean and Indo-West Pacific as it is to West or East Atlantic faunas.     

On functional morphology of the skeleton in lychnisc sponges (Porifera,Hexactinellida)

By comparison with architectural models it can be shown that both the “euretoid” arrangement of fused spicules and lychnisc node itself should enhance the strength of the skeleton of the Lychniscosa. Contrary to expectation however, the Lychniscosa do not inhabit more turbulent waters than the Hexactinosa with a simpler skeletal structure. Possible reasons for this are discussed.     

The filtration apparatus for food collection in freshwater sponges (Porifera,Spongillidae)

Summary The freshwater sponges (Spongillidae) feed by filtering out small particles from the water passing through them by means of strainer devices in the flagellated chambers. These are filamentous, fine-meshed structures at the distal ends of the choanocyte collars formed of a mucous material similar to that in the glycocalyx. Each strainer separates its flagellated chamber into an outer and an inner zone. The strainers are an extremely efficient filtering mechanism.     

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.     

Freshwater sponge fauna (Porifera) of coastal waters of India

Wetlands Ecology and Management - India has a long coastal line, measuring over seven thousand kilometers, along eight States and some Union Territories. In addition to marine ecosystems along this...     

Screening of the Antarctic marine sponges (Porifera) as a source of bioactive compounds

Sponges (Porifera) currently represent one of the richest sources of natural products and account for almost half of the pharmacologically active compounds of marine origin. However, to date very little is known about the pharmacological potential of the sponges from polar regions. In this work we report on screening of ethanolic extracts from 24 Antarctic marine sponges for different biological activities. The extracts were tested for cytotoxic effects against normal and transformed cell lines, red blood cells, and algae, for modulation of the activities of selected physiologically important enzymes (acetylcholinesterase, butyrylcholinesterase, and α-amylase), and for inhibition of growth of pathogenic and ecologically relevant bacteria and fungi. An extract from Tedania (Tedaniopsis) oxeata was selectively cytotoxic against the cancer cell lines and showed growth inhibition of all of the tested ecologically relevant and potentially pathogenic fungal isolates. The sponge extracts from Isodictya erinacea and Kirkpatrickia variolosa inhibited the activities of the cholinesterase enzymes, while the sponge extracts from Isodictya lankesteri and Inflatella belli reduced the activity of α-amylase. Several sponge extracts inhibited the growth of multiresistant pathogenic bacterial isolates of different origins, including extended-spectrum beta-lactamase and carbapenem-resistant strains, while sponge extracts from K. variolosa and Myxilla (Myxilla) mollis were active against a human methicillin-resistant Staphylococcus aureus strain. We conclude that Antarctic marine sponges represent a valuable source of biologically active compounds with pharmacological potential.     

The problem of germ layers in sponges (Porifera) and some issues concerning early metazoan evolution

Nowadays the formation of germ layers (endoderm and mesoderm) is associated with gastrulation. The question of whether the cell movements during early embryonic development in sponges (Porifera) are gastrulation as in eumetazoans remains in dispute. Recent data on the histological organization, digestion and embryonic morphogenesis in sponges are analyzed here in an attempt to answer this question. Unique features of these basal Metazoa are the lack of intestinal epithelium, digestive parenchyma or any cell population specialized in digestion. Food particles are captured by cells of almost all types. These data show that sponges have no embryonic layers such as ectoderm or endoderm, characteristic to eumetazoans, and, consequently, no gastrulation. We make an assumption that the formation of germ layers cannot be considered as a recapitulation of events that took place in the common ancestor of Porifera and Eumetazoa. The unity of Metazoa is expressed not in the presence of gastrulation processes per se, but in the universal nature of cell movement mechanisms ensuring various types of morphogenesis, including those underlying gastrulation. It is concluded that metazoan mechanisms of morphogenetic movements must have emerged in the course of evolution prior to the separation of the germ layers like endoderm and ectoderm.