Integrating morphological and molecular taxonomy with the revised concept of Stelligeridae (Porifera: Demospongiae)

This study reinforces and extends the findings of previous molecular studies showing that there is a close relationship between species assigned to the sponge genera Halicnemia, Higginsia, Paratimea and Stelligera and that the family Heteroxyidae is polyphyletic. The present study has led to the description of one new species of Halicnemia and six new species of Paratimea, the resurrection of Halicnemia gallica and a better understanding of the characters uniting Stelligeridae. A new species of Heteroxya is also described. We demonstrate that many of the taxa assigned to Heteroxyidae are more closely related to other families, and we propose several changes to the classification of Heteroscleromorpha. Desmoxyidae is resurrected from synonymy and transferred to Poecilosclerida; Higginsia anfractuosa is transferred to Hymedesmiidae, and a new genus, Hooperia, is erected for its reception; Higginsia durissima is returned to Bubaris (Bubaridae); Higginsia fragilis is transferred to Spanioplon (Hymedesmiidae); Hemiasterella camelus is transferred to Paratimea; and Raspailia (Parasyringella) australiensis and Ceratopsion axiferum are transferred to Adreus (Hemiasterellidae).

Sponge inventory of the French Mediterranean waters, with an emphasis on cave-dwelling species

Mediterranean sponges represent about 10 % of the world sponge biodiversity, with these sessile organisms dominating in terms of diversity and biomass in most of the rocky bottoms shaded from light. After 60 years of intensive study of the sponge diversity along the French coast, we present the first comprehensive reference-list for this biogeographic area. A total of 389 sponge species was recorded, of which 222 known in the Marseille region. In this area, special attention was paid to species from underwater caves. Although this particular habitat appeared as one of the richest, a wealth of hidden diversity still requires description. About 37 % of the sponge diversity can be found in underwater caves, most of these species being also distributed in other habitats. However, 23 % of this sponge diversity is cave-exclusive. An easy and rapid assessment method was developed with a selection of 65 representative sponge species, for the monitoring of semi-dark cave communities. This method, based on data acquisition with photoquadrats and their processing using a DataBase built with ACCESS, was deployed in 13 studied sites. Altogether, this study represents a useful contribution for marine environment managers who might refer to this French reference list and apply the rapid and easy assessment method in the framework of several European Directives and international Conventions.

Systematic account of new Porifera (Demospongiae) records from the oceanic Island of Madeira (NE Atlantic)

Few surveys on benthic fauna have been performed on the island of Madeira (Alves et al. 2003 and references therein), and the first sponge specimens were collected opportunistically (Johnson 1863, 1899; Topsent 1904, 1928). Porifera can be considered one of the least studied phyla in the Madeira archipelago, within the Lusitanian province. This is not the case for other regions as the Mediterranean (Boury-Esnault 1971 and references therein), Alboran Sea (Carballo 1994), Canary Islands (Cruz 2002), and the Azores (Topsent 1904; Boury-Esnault Lopes 1985; Xavier 2009), where sponges have been more thoroughly studied.

DOES COSMOPOLITANISM RESULT FROM OVERCONSERVATIVE SYSTEMATICS? A CASE STUDY USING THE MARINE SPONGE CHONDRILLA NUCULA

The sponge species Chondrilla nucula has a simple morphology and a very wide geographical distribution. To verify whether the latter might be an artifact of the former, samples of this species were collected across 10,000 km of its range, in the Mediterranean, the Caribbean, and the southwestern atlantic. The classical (spicule morphology) and molecular (allozymes) systematic approaches were compared, to try to define the geographic limits between populations and detect possible cryptic species. We found five distinct genetic forms within C. nucula that sometimes showed morphological homogeneity and other times plasticity. The difference in size of spicules could not be related to the clear-cut genetic differences, suggesting that the use of spicule sizes for sponge systematics should be reappraised. The population of one of the genetic forms along 3000 km of the Brazilian coast was highly structured (F_ST = 0.21; N_e m = 0.96). Our results reject the null hypothesis of cosmopolitanism of C. nucula and indicate that the putative worldwide distribution of some marine sponges, and possibly many other benthic invertebrates, may be the result of overly conservative systematics. Cryptic species appear to be particularly prevalent when genera are well defined but species are characterized by only a few morphological characters.

How a collaborative integrated taxonomic effort has trained new spongiologists and improved knowledge of Martinique Island (French Antilles, eastern Caribbean Sea) marine biodiversity

Although sponges are important components of benthic ecosystems of the Caribbean Sea, their diversity remained poorly investigated in the Lesser Antilles. By organizing a training course in Martinique, we wanted both to promote taxonomy and to provide a first inventory of the sponge diversity on this island. The course was like a naturalist expedition, with a field laboratory and a classroom nearby. Early-career scientists and environmental managers were trained in sponge taxonomy. We gathered unpublished data and conducted an inventory at 13 coastal sites. We explored only shallow water habitats (0–30 m), such as mangroves, reefs or rocky bottoms and underwater caves. According to this study, the sponge fauna of Martinique is currently represented by a minimum of 191 species, 134 of which we could assign species names. One third of the remaining non-identified sponge species we consider to be new to science. Martinique appears very remarkable because of its littoral marine fauna harboring sponge aggregations with high biomass and species diversity dominating over coral species. In mangroves, sponges cover about 10% of the surface of subtidal roots. Several submarine caves are true reservoirs of hidden and insufficiently described sponge diversity. Thanks to this new collaborative effort, the Eastern Caribbean has gained a significant increase of knowledge, with sponge diversity of this area potentially representing 40% of the total in the Caribbean Sea. We thus demonstrated the importance of developing exploratory and educational research in areas historically devoid of biodiversity inventories and systematics studies. Finally, we believe in the necessity to consider not only the number of species but their distribution in space to evaluate their putative contribution to ecosystem services and our willingness to preserve them.

The systematics of carnivorous sponges

Carnivorous sponges are characterized by their unique method of capturing mesoplanktonic prey coupled with the complete or partial reduction of the aquiferous system characteristic of the phylum Porifera. Current systematics place the vast majority of carnivorous sponges within Cladorhizidae, with certain species assigned to Guitarridae and Esperiopsidae. Morphological characters have not been able to show whether this classification is evolutionary accurate, and whether carnivory has evolved once or in several lineages. In the present paper we present the first comprehensive molecular phylogeny of the carnivorous sponges, interpret these results in conjunction with morphological characters, and propose a revised classification of the group. Molecular phylogenies were inferred using 18S rDNA and a combined dataset of partial 28S rDNA, COI and ALG11 sequences. The results recovered carnivorous sponges as a clade closely related to the families Mycalidae and Guitarridae, showing family Cladorhizidae to be monophyletic and also including carnivorous species currently placed in other families. The genus Lycopodina is resurrected for species currently placed in the paraphyletic subgenus Asbestopluma (Asbestopluma) featuring forceps spicules and lacking sigmas or sigmancistras. The genera Chondrocladia and Cladorhiza are found to be monophyletic. However, results indicate that the subgenus Chondrocladia is polyphyletic with respect to the subgenera Meliiderma and Symmetrocladia. Euchelipluma, formerly Guitarridae, is retained, but transferred to Cladorhizidae. The four known carnivorous species currently in Esperiopsis are transferred to Abyssocladia. Neocladia is a junior homonym and is here renamed Koltunicladia. Our results provide strong evidence in support of the hypothesis that carnivory in sponges has evolved only once. While spicule characters mostly reflect monophyletic groups at the generic level, differences between genera represent evolution within family Cladorhizidae rather than evolution of carnivory in separate lineages. Conflicting spicule characters can be reinterpreted to support the inclusion of all carnivorous sponges within Cladorhizidae, and a carnivorous habit should thus be considered the main diagnostic character in systematic classification.

The integrative taxonomic approach applied to porifera: a case study of the homoscleromorpha

The two main scientific tasks of taxonomy are species' delineation and classification. These two tasks are often treated differently, with classification accomplished by newly-developed phylogenetic methods, often based on molecular sequences, while delimitation of species is conducted by what is often considered to be an "old-fashioned" typological approach based on morphological description. A new "integrative taxonomy" has been proposed which maintains that species delimitation should be a multidisciplinary undertaking combining several independent datasets. Here we argue that the same principle is relevant to the classification of species. In the past 20 years, we assembled various datasets based on the external morphology, anatomy, cytology, spicule shapes, geography, reproduction, genetic sequences, and metabolomics of homoscleromorph sponges. We show how we used these datasets to describe new species of homoscleromorph sponges and to elucidate their phylogenetic relationships and their phylogenetic position within the phylum Porifera.

Reconstruction of family-level phylogenetic relationships within Demospongiae (Porifera) using nuclear encoded housekeeping genes

BACKGROUND

Demosponges are challenging for phylogenetic systematics because of their plastic and relatively simple morphologies and many deep divergences between major clades. To improve understanding of the phylogenetic relationships within Demospongiae, we sequenced and analyzed seven nuclear housekeeping genes involved in a variety of cellular functions from a diverse group of sponges.

METHODOLOGY/PRINCIPAL FINDINGS

We generated data from each of the four sponge classes (i.e., Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha), but focused on family-level relationships within demosponges. With data for 21 newly sampled families, our Maximum Likelihood and Bayesian-based approaches recovered previously phylogenetically defined taxa: Keratosa(p), Myxospongiae(p), Spongillida(p), Haploscleromorpha(p) (the marine haplosclerids) and Democlavia(p). We found conflicting results concerning the relationships of Keratosa(p) and Myxospongiae(p) to the remaining demosponges, but our results strongly supported a clade of Haploscleromorpha(p)+Spongillida(p)+Democlavia(p). In contrast to hypotheses based on mitochondrial genome and ribosomal data, nuclear housekeeping gene data suggested that freshwater sponges (Spongillida(p)) are sister to Haploscleromorpha(p) rather than part of Democlavia(p). Within Keratosa(p), we found equivocal results as to the monophyly of Dictyoceratida. Within Myxospongiae(p), Chondrosida and Verongida were monophyletic. A well-supported clade within Democlavia(p), Tetractinellida(p), composed of all sampled members of Astrophorina and Spirophorina (including the only lithistid in our analysis), was consistently revealed as the sister group to all other members of Democlavia(p). Within Tetractinellida(p), we did not recover monophyletic Astrophorina or Spirophorina. Our results also reaffirmed the monophyly of order Poecilosclerida (excluding Desmacellidae and Raspailiidae), and polyphyly of Hadromerida and Halichondrida.

CONCLUSIONS/SIGNIFICANCE

These results, using an independent nuclear gene set, confirmed many hypotheses based on ribosomal and/or mitochondrial genes, and they also identified clades with low statistical support or clades that conflicted with traditional morphological classification. Our results will serve as a basis for future exploration of these outstanding questions using more taxon- and gene-rich datasets.

Global diversity of sponges (Porifera)

With the completion of a single unified classification, the Systema Porifera (SP) and subsequent development of an online species database, the World Porifera Database (WPD), we are now equipped to provide a first comprehensive picture of the global biodiversity of the Porifera. An introductory overview of the four classes of the Porifera is followed by a description of the structure of our main source of data for this paper, the WPD. From this we extracted numbers of all 'known' sponges to date: the number of valid Recent sponges is established at 8,553, with the vast majority, 83%, belonging to the class Demospongiae. We also mapped for the first time the species richness of a comprehensive set of marine ecoregions of the world, data also extracted from the WPD. Perhaps not surprisingly, these distributions appear to show a strong bias towards collection and taxonomy efforts. Only when species richness is accumulated into large marine realms does a pattern emerge that is also recognized in many other marine animal groups: high numbers in tropical regions, lesser numbers in the colder parts of the world oceans. Preliminary similarity analysis of a matrix of species and marine ecoregions extracted from the WPD failed to yield a consistent hierarchical pattern of ecoregions into marine provinces. Global sponge diversity information is mostly generated in regional projects and resources: results obtained demonstrate that regional approaches to analytical biogeography are at present more likely to achieve insights into the biogeographic history of sponges than a global perspective, which appears currently too ambitious. We also review information on invasive sponges that might well have some influence on distribution patterns of the future.

Sponge systematics facing new challenges

Systematics is nowadays facing new challenges with the introduction of new concepts and new techniques. Compared to most other phyla, phylogenetic relationships among sponges are still largely unresolved. In the past 10 years, the classical taxonomy has been completely overturned and a review of the state of the art appears necessary. The field of taxonomy remains a prominent discipline of sponge research and studies related to sponge systematics were in greater number in the Eighth World Sponge Conference (Girona, Spain, September 2010) than in any previous world sponge conferences. To understand the state of this rapidly growing field, this chapter proposes to review studies, mainly from the past decade, in sponge taxonomy, nomenclature and phylogeny. In a first part, we analyse the reasons of the current success of this field. In a second part, we establish the current sponge systematics theoretical framework, with the use of (1) cladistics, (2) different codes of nomenclature (PhyloCode vs. Linnaean system) and (3) integrative taxonomy. Sponges are infamous for their lack of characters. However, by listing and discussing in a third part all characters available to taxonomists, we show how diverse characters are and that new ones are being used and tested, while old ones should be revisited. We then review the systematics of the four main classes of sponges (Hexactinellida, Calcispongiae, Homoscleromorpha and Demospongiae), each time focusing on current issues and case studies. We present a review of the taxonomic changes since the publication of the Systema Porifera (2002), and point to problems a sponge taxonomist is still faced with nowadays. To conclude, we make a series of proposals for the future of sponge systematics. In the light of recent studies, we establish a series of taxonomic changes that the sponge community may be ready to accept. We also propose a series of sponge new names and definitions following the PhyloCode. The issue of phantom species (potential new species revealed by molecular studies) is raised, and we show how they could be dealt with. Finally, we present a general strategy to help us succeed in building a Porifera tree along with the corresponding revised Porifera classification.

Axiphenylalaninium and axityrosinium, modified amino acids from the Mediterranean marine sponge Axinella polypoides

Two new modified amino acids, axiphenylalaninium (1) and axityrosinium (2), along with four known metabolites, C2-alpha-D-mannosylpyranosyl-L-tryptophan (3), N3,5'-cycloxanthosine (4), palythine (5), and taurine, were isolated from the marine sponge Axinella polypoides collected in the Mediterranean Sea. The structures were determined by spectroscopic studies and confirmed by X-ray analysis and chemical modifications.

Phylogenomics revives traditional views on deep animal relationships

The origin of many of the defining features of animal body plans, such as symmetry, nervous system, and the mesoderm, remains shrouded in mystery because of major uncertainty regarding the emergence order of the early branching taxa: the sponge groups, ctenophores, placozoans, cnidarians, and bilaterians. The "phylogenomic" approach [1] has recently provided a robust picture for intrabilaterian relationships [2, 3] but not yet for more early branching metazoan clades. We have assembled a comprehensive 128 gene data set including newly generated sequence data from ctenophores, cnidarians, and all four main sponge groups. The resulting phylogeny yields two significant conclusions reviving old views that have been challenged in the molecular era: (1) that the sponges (Porifera) are monophyletic and not paraphyletic as repeatedly proposed [4-9], thus undermining the idea that ancestral metazoans had a sponge-like body plan; (2) that the most likely position for the ctenophores is together with the cnidarians in a "coelenterate" clade. The Porifera and the Placozoa branch basally with respect to a moderately supported "eumetazoan" clade containing the three taxa with nervous system and muscle cells (Cnidaria, Ctenophora, and Bilateria). This new phylogeny provides a stimulating framework for exploring the important changes that shaped the body plans of the early diverging phyla.

Sponge paraphyly and the origin of Metazoa

In order to allow critical evaluation of the interrelationships between the three sponge classes, and to resolve the question of mono- or paraphyly of sponges (Porifera), we used the polymerase chain reaction (PCR) to amplify almost the entire nucleic acid sequence of the 18S rDNA from several hexactinellid, demosponge and calcareous sponge species. The amplification products were cloned, sequenced and then aligned with previously reported sequences from other sponges and nonsponge metazoans and variously distant outgroups, and trees were constructed using both neighbour-joining and maximum parsimony methods. Our results suggest that sponges are paraphyletic, the Calcarea being more related to monophyletic Eumetazoa than to the siliceous sponges (Demospongiae, Hexactinellida). These results have important implications for our understanding of metazoan origins, because they suggest that the common ancestor of Metazoa was a sponge. They also have consequences for basal metazoan classification, implying that the phylum Porifera should be abandoned. Our results support the upgrading of the calcareous sponge class to the phylum level.

NK homeobox genes with choanocyte-specific expression in homoscleromorph sponges

Data on nonbilaterian animals (sponges, cnidarians, and ctenophores) have suggested that Antennapedia (ANTP) class homeobox genes played a crucial role in the early diversification of animal body plans. Estimates of ancestral gene diversity within this important class of developmental regulators have been mostly based on recent analyses of the complete genome of a demosponge species, leading to the proposal that all ANTP families found in nonsponges animals (eumetazoans) derived from an ancestral "proto-NK" six-gene cluster. However, a single sponge species cannot reveal ancestral metazoan traits, in particular because lineage-specific gene duplications or losses are likely to have occurred during the long history of the Porifera. We thus looked for ANTP genes by degenerate polymerase chain reaction search in five species belonging to the Homoscleromorpha, a sponge lineage recently phylogenetically classified outside demosponges and characterized by unique histological features. We identified new genes of the ANTP class called HomoNK. Our phylogenetic analyses placed HomoNK (without significant support) close to the NK6 and NK7 families of cnidarian and bilaterian ANTP genes and did not recover the monophyly of the proposed "proto-NK" cluster. Our expression analyses of the HomoNK gene OlobNK in adult Oscarella lobularis showed that this gene is a strict marker of choanocytes, the most typical sponge cell type characterized by an apical flagellum surrounded by a collar of microvilli. These results are discussed in the light of the predominant neurosensory expression of NK6 and NK7 genes in bilaterians and of the recent proposal that choanocytes could be the sponge homologs of sensory cells.

Agelasines J, K, and L from the Solomon Islands Marine Sponge Agelas cf. mauritiana

Three new diterpene alkaloids, agelasine J (3), agelasine K (4), and agelasine L (5), were isolated from the marine sponge Agelas cf. mauritiana collected in the Solomon Islands. The structures of these compounds were elucidated by physical data analyses. They displayed in vitro antimalarial activity against Plasmodium falciparum.

Metamorphosis of cinctoblastula larvae (Homoscleromorpha, porifera)

The metamorphosis of the cinctoblastula of Homoscleromorpha is studied in five species belonging to three genera. The different steps of metamorphosis are similar in all species. The metamorphosis occurs by the invagination and involution of either the anterior epithelium or the posterior epithelium of the larva. During metamorphosis, morphogenetic polymorphism was observed, which has an individual character and does not depend on either external or species specific factors. In the rhagon, the development of the aquiferous system occurs only by epithelial morphogenesis and subsequent differentiation of cells. Mesohylar cells derive from flagellated cells after ingression. The formation of pinacoderm and choanoderm occurs by the differentiation of the larval flagellated epithelium. This is possibly due to the conservation of cell junctions in the external surface of the larval flagellated cells and of the basement membrane in their internal surface. The main difference in homoscleromorph metamorphosis compared with Demospongiae is the persistence of the flagellated epithelium throughout this process and even in the adult since exo- and endopinacoderm remain flagellated. The antero-posterior axis of the larva corresponds to the baso-apical axis of the adult in Homoscleromorpha.

Conservation and Phylogeny of a Novel Family of Non-Hox Genes of the Antp Class in Demospongiae (Porifera)

A survey across the most basal animal phylum, the Porifera, for the presence of homeobox-containing genes led to the isolation of 24 partial or complete homeobox sequences from 21 sponge species distributed in 15 families and 6 orders of Demospongiae. All the new sequences shared a high identity/similarity with EmH-3 (Ephydatia muelleri), a non-Hox gene from the Antp class. The Demox sequences, EmH-3, and related homeodomains formed a well-supported clade with no true affinity with any known bilaterian family, including the Tlx/Hox11 family, suggesting that the EmH-3 family of genes, comprising 31 members, represents a novel family of non-Hox genes, called the Demox family, widespread among Demospongiae. The presence of the Tlx/Hox11 specific signature in the Demox family and common regulatory elements suggested that the Demox and Tlx/Hox11 families are closely related. In the phylogenetic analyses, freshwater Haplosclerida appeared as monophyletic, and Haplosclerida and Halichondrida as polyphyletic, with a clade comprising Agelas species and Axinella corrugata. As for their expression, high levels of Demox transcripts were found in adult tissues. Our data add to the number of published poriferan homeobox sequences and provide independent confirmation of the current Demospongiae phylogenies.

Verpacamides A−D, a Sequence of C11N5 Diketopiperazines Relating Cyclo(Pro-Pro) to Cyclo(Pro-Arg), from the Marine Sponge Axinella vaceleti: Possible Biogenetic Precursors of Pyrrole-2-aminoimidazole Alkaloids

[reaction: see text] Four C(11)N(5) diketopiperazine metabolites named verpacamides A (6), B (7), C (8), and D (9) consisting of a proline-arginine dipeptide skeleton have been isolated from the marine sponge Axinella vaceleti. Verpacamides A-D are a sequence of metabolites showing the transformation of proline and arginine into the oxidized guanidinyl-cyclo(Pro-Pro) 8 and 9. Compounds 6-9 are structurally and chemically related to C(11)N(5) pyrrole-2-aminoimidazole metabolites also isolated from the Axinellidae and Agelasidae families of sponges and exemplified by dispacamide A (4) and dibromophakellin (10).

Embryogenesis in the glass sponge Oopsacas minuta: Formation of syncytia by fusion of blastomeres

Sponges (Porifera) are unusual animals whose body plans make interpreting phylogenetic relationships within the group and with other basal metazoan taxa a difficult task. Although molecular approaches have offered new insights, some questions require a morphological approach using detailed ultrastructural or light microscopical studies of developing embryos and larvae. Glass sponges (Hexactinellida) have perhaps the most unusual body plan within the Metazoa because the majority of the tissue of the adult consists of a single giant multinucleated syncytium that forms the inner and outer layers of the sponge and is joined by cytoplasmic bridges to uninucleate cellular regions. Here we have used serial section transmission and high-resolution scanning electron microscopy to examine when syncytia first form in the cave-dwelling glass sponge Oopsacas minuta. We confirm that in O. minuta blastomeres are separate until the 32-cell stage; cleavage is equal but asynchronous until a hollow blastula is formed. The sixth division yields a collection of variously sized micromeres at the surface of the embryo and large yolk- and lipid-filled macromeres lining the blastocoel. Syncytia then form by the fusion of micromeres to form cytoplasmic bridges with each other and the fusion of macromeres to form the future multinucleated trabecular tissue of the larva and adult sponge. The multinucleated trabecular tissue envelops and forms cytoplasmic bridges with all uninucleate cells, covering the developing larva with a continuous syncytial epithelium. Differentiation of tissues occurs very early during embryogenesis with the separation of uninucleate and multinucleate lineages, but all cells and syncytia are joined by cytoplasmic bridges such that there is cytoplasmic continuity throughout the entire larva. Although glass sponges begin life as a cellular embryo, the unusual mechanism of syncytia formation at such an early stage in development distinguishes this group of animals from their closest multicellular relatives, the Demospongiae. Most important, however, these data lend support to the hypothesis that the original metazoans were cellular, not syncytial.

Systematics and evolution of Demospongiae

Systematic and evolutionary studies of Demospongiae Sollas, 1885 are a very dynamic field of research. The scientific knowledge pertaining to Demospongiae systematics has been recently assembled in the collective book Systema Porifera. However, a general consensus among spongologists has not yet been achieved regarding this group and the phylogenetic relationships within Demospongiae and between Demospongiae and other clades of Porifera and metazoans are still unresolved. The two traditional subclasses Tetractinomorpha and Ceractinomorpha are polyphyletic and it is proposed that they be abandoned. Since the publication of Systema Porifera, several works have suggested the polyphyly of Halichondrida and the paraphyly of Haplosclerida, as well as the monophyly of Tetractinellida (Astrophorida + Spirophorida), Keratosa (Dictyoceratida + Dendroceratida), and Myxospongiae (Chondrosida + Verongida + Halisarcida). Within all the classical orders, whether they are monophyletic or not, families and even genera have also been found to be polyphyletic. For example, Ancorinidae, Geodiidae, and Axinellidae are clearly polyphyletic. No single data set is able to resolve all the problems; thus, it is absolutely necessary that the classification of Demospongiae be examined from all angles and with as many data sets as possible.

Molecular phylogeny of Demospongiae: implications for classification and scenarios of character evolution

An analysis of the phylogenetic relationships of the 13 orders of Demospongiae, based on 18S and C1, D1 and C2 domains of 28S rRNA (for, respectively, 26 and 32 taxa) has been performed. The class Demospongiae as traditionally defined is not found to be monophyletic. Instead, a clade comprising all demosponges except Homoscleromorpha is well-supported, and we define phylogenetically the name Demospongiae in this more restricted sense to preclude the possibility of drastic alterations of the meaning of Demospongiae in the future, depending on the position of Homoscleromorpha. Within this clade Demospongiae s.s., ceractinomorphs and tetractinomorphs are polyphyletic, implying homoplastic evolution of characters such as reproductive strategies (viviparity vs. oviparity) and skeleton architecture (reticulate vs. radiate). The topology derived from our molecular data provides a basis for proposing a new classification of Demospongiae s.s., and suggests a reverse polarity of some characters, with respect to traditional conceptions: viviparity, presence of monaxon spicules and of spongin appear to be ancestral, whereas oviparity, and presence of tetraxon spicules appear as derived characters.

Phylogeny and evolution of calcareous sponges: monophyly of calcinea and calcaronea, high level of morphological homoplasy, and the primitive nature of axial symmetry

Because calcareous sponges are triggering renewed interest with respect to basal metazoan evolution, a phylogenetic framework of their internal relationships is needed to clarify the evolutionary history of key morphological characters. Morphological variation was scored at the suprageneric level within Calcispongia, but little phylogenetic information could be retrieved from morphological characters. For the main subdivision of Calcispongia, the analysis of morphological data weakly supports a classification based upon cytological and embryological characters (Calcinea/Calcaronea) rather than the older classification scheme based upon the aquiferous system (Homocoela/Heterocoela). The 18S ribosomal RNA data were then analyzed, both alone and in combination with morphological characters. The monophyly of Calcispongia is highly supported, but the position of this group with respect to other sponge lineages and to eumetazoan taxa is not resolved. The monophyly of both Calcinea and Calcaronea is retrieved, and the data strongly rejected the competing Homocoela/Heterocoela hypothesis. The phylogeny implies that characters of the skeleton architecture are highly homoplastic, as are characters of the aquiferous system. However, axial symmetry seems to be primitive for all Calcispongia, a conclusion that has potentially far-reaching implications for hypotheses of early body plan evolution in Metazoa.

Reassessment of homology of morphological characters in tetractinellid sponges based on molecular data

In sponges, as in other taxa with simple organization, the evaluation and use of morphological characters is difficult. Phylogenetic analysis of the first 850 nucleotides from the 5' end of the 28S rRNA gene is used here to assess the homology of spicules used in the classification of the subclass Tetractinellida. A single well-supported MP tree was obtained. The monophyly of the nine Tetractinellida species studied confirms the tetraxon megasclere as a morphological synapomorphy for the Tetractinellida. Two species are reallocated, Penares helleri as a Geodiidae, now thought to have lost sterraster microscleres, and Stryphnus mucronatus to the Streptosclerophorida. SEM micrographs of Stryphnus microscleres show that the morphology of the sanidasters is compatible with the hypothesis that they are homologous with streptoscleres and confirm this reallocation. Two other synapomorphies are confirmed within the tetractinellid clade, the simultaneous presence of tetraxon megasclere and aster-type microsclere (Astrophorida) and the loss of the streptosclere and persistence of the euaster s.s. microscleres (Euastrophorida) evidenced by the reallocation of Stryphnus mucronatus. The streptosclere microscleres cannot be evaluated in terms of homology because Streptosclerophorida may be paraphyletic (although these nodes are not supported by reliable bootstrap proportions) contrary to the currently accepted classification.

Phylogenetic analysis of the Hsp70 sequences reveals the monophyly of Metazoa and specific phylogenetic relationships between animals and fungi

To understand the early evolution of the Metazoa, it is necessary to determine the correct phylogenetic status of diploblastic animals. Despite cladistic studies of morphological characters and recent molecular phylogenetic studies, it remains uncertain whether diploblasts are monophyletic or paraphyletic, and how the phyla of diploblasts are phylogenetically related. The heat shock protein 70 (Hsp70) sequences, because of their ubiquity and high degree of conservation, could provide a useful model for phylogenetic analysis. We have sequenced almost the entire nucleic acid sequence of cytoplasmic Hsp70 from eight diploblastic species. Our data support the monophyly of diploblastic animals. However, the phylogenetic relationships of the diploblast groups were not significantly resolved. Our phylogenetic trees also support the monophyly of Metazoa with high bootstrap values, indicating that animals form an extremely robust clade.

Polyphyly of "sclerosponges" (Porifera, Demospongiae) supported by 28S ribosomal sequences

To test the competing hypotheses of polyphyly and monophyly of "sclerosponges," sequences from the 5' end of 28S ribosomal RNA were obtained for Astrosclera willeyana, Acanthochaetetes wellsi, and six other demosponge species. Phylogenetic relationships deduced from parsimony and neighbor-joining analyses suggest that these sclerosponges belong to two different orders of Demospongiae: Astrosclera willeyana, being closely related to the Agelasidae, belongs to the Agelasida, Acanthochaetetes wellsi, being closely related to the Spirastrellidae, belongs to the Hadromerida. These results contradict the hypothesis that sclerosponges are monophyletic and imply that a massive calcareous skeleton has evolved independently in several lineages of sponges.

Sponge phylogeny, animal monophyly, and the origin of the nervous system: 18S rRNA evidence

We sequenced 18S rRNA genes of a calcareous sponge, Clathrina cerebrum, a demosponge, Axinella polypoides, and a zoanthid cnidarian, Parazoanthus axinellae. Our phylogenetic analysis supports the monophyly of kingdom Animalia and confirms that choanoflagellate protozoans are their closest relatives. Sponges as a whole are monophyletic, but possibly paraphyletic; demosponges and hexactinellids form a monophyletic group of silicious sponges. Our phylogenetic trees support a monophyletic origin of the nervous system in the immediate common ancestor of Cnidaria and Ctenophora. They weakly suggest that animals with a nervous system may be more closely related to calcareous sponges than to silicious sponges; the nervous system might have originated in an early calcareous sponge. Our trees confirm that Myxozoa and Placozoa are animals that arose by secondary loss of the nervous system, but suggest that Myxozoa may be sisters of, rather than derived from, Bilateria. Kingdom Animalia is divided into four subkingdoms: Radiata (Porifera, Cnidaria, Placozoa, Ctenophora), Myxozoa, Mesozoa, and Bilateria. The 18S rRNA genes of Myxozoa evolved over twice as fast as in Radiata. Comparison with the fossil record reveals a brief 10-fold (or greater) acceleration in the rate of rRNA evolution in early Bilateria followed by normal low rates for about 500 million years.

Cytological evidence for cryptic speciation in MediterraneanOscarellaspecies (Porifera, Homoscleromorpha)

Three new sponge species without a skeleton, Oscarella viridis, O. microlobata, and O. imperialis, were found in sublittoral caves and on vertical walls along the coast of Provence (western Mediterranean Sea, France). Their morphology, anatomy, and cytology are described and they are compared with the two other valid Mediterranean Oscarella species, O. lobularis and O. tuberculata. Reproductive and internal anatomical characters are uniform in the genus, but details of external morphology and especially cytological characters (mesohylar cells with inclusions) provide good diagnostic features at the species level. Careful observation of morphological and cytological characters is essential for clarifying the systematics of Oscarella and reveals an unexpected biodiversity of this genus in the Mediterranean Sea.

Type IV collagen in sponges, the missing link in basement membrane ubiquity

Basement membrane structures, or their main component, type IV collagen, have been detected in all multicellular animal species, except sponges. We cancel this exception by the demonstration of type IV collagenous sequences in a new marine sponge species by cDNA and genomic DNA studies. One of these sequences is long enough to demonstrate the specific characteristics of type IV collagen chains. The 12 cysteines are at conserved positions in the carboxyl-terminal non-helical NCl domain, as are the interruptions in the carboxyl-terminal end of the triple helical domain. The gene organization of the region coding for the NCl domain is similar to that of the human genes COL4A2, COL4A4 and COL4A6. An additional, shorter sequence suggests the presence of a second chain. The expected tissue localization of this collagen has been confirmed using polyclonal antibodies raised against a sponge recombinant protein. These results demonstrate that type IV collagen is representated in all animal phyla. It is actually the only known ubiquitous collagen and it has at least two different alpha chains in all the species where it has been characterized.

The value of cytological criteria in distinguishing sponges at the species level: the example of the genus Polymastia

We examined the value of using cytological criteria for sponge taxonomy within the well-defined genus Polymastia and redescribe the species Polymastia janeirensis comb.nov. Comparison of the anatomical, morphological, and skeletal characteristics of P. janeirensis with those of the 17 other known Atlantic species demonstrated that P. janeirensis is closely related to P. agglutinans and P. mammillaris. The study confirmed that the close relationship between P. janeirensis and P. mammillaris can also be recognized at the cytological level. We conclude that cytological criteria can be used for the identification of sponges at the species level, and that these criteria may provide useful information about phylogenetic relationships among sponges belonging to genera with many species and a wide geographical distribution.

An analysis of partial 28S ribosomal RNA sequences suggests early radiations of sponges

Sequences from the 5' end terminal part of 28S ribosomal RNA were obtained and compared for 22 animals belonging to all diploblastic phyla and for a large number of representatives of triploblastic Metazoa and protists. Phylogenetic analyses undertaken using different methods showed deep radiations of phyla such as Ctenophora, Cnidaria and Placozoa but also for groups of Porifera of low taxonomic rank. Short internodes between these radiations suggested an early rapid diversification of diploblasts. A long internal branch preceding the diversification of all triploblasts analyzed could be explained either by a long period with a single ancestor or by the extinction of the earliest triploblastic radiations. Finally some unexpected relationships were revealed among Porifera.

Comparative study of the choanosome of Porifera: 1. The Homoscleromorpha

The choanoderm and pinacoderm of representatives of the two families of Homoscleromorpha sponges, the Oscarellidae and Plakinidae, have been examined by transmission and scanning electron microscopy. Different fixative procedures have shown the dramatic influence of fixation conditions on the morphology of choanocytes. These two families of sponges have the following morphological features in common: flagellated endopinacocytes with short apical microvilli and basal pseudopods; the presence of a very thin and dense sheet of matrix material which limits the mesohyl. There are, however, only minor differences in the flagellar morphology, granule content, and anchoring system of their choanocytes. Two findings are of particular interest: (1) the presence of glycocalyx bridges between the microvilli of the choanocyte collar; and (2) the discovery of a new cell type, the apopylar cell, which has a morphology intermediate between that of pinacocytes and choanocytes. The apopylar cells limit the apopylar opening of the choanocyte chamber and indicate the transition between choanoderm and pinacoderm.

A cell type in sponges involved in the metabolism of glycogen. The gray cells

The gray cells of four orders of demosponges contain basophilic inclusions and glycogen. They are capable of synthesis and accumulation of glycogen and responsible for its transfer to sites of more intense metabolism (growth, bud, blastema). They do not occur in larvae; but all the phases of their differentiation from the flagellar cells of the larva have been demonstrated.