Identification, characterization and phylogenetic signal of an elongation factor-1 alpha fragment in demosponges (Metazoa, Porifera, Demospongiae)

Deep phylogeny and evolution of sponges (phylum Porifera)

Sponges (phylum Porifera) are a diverse taxon of benthic aquatic animals of great ecological, commercial, and biopharmaceutical importance. They are arguably the earliest-branching metazoan taxon, and therefore, they have great significance in the reconstruction of early metazoan evolution. Yet, the phylogeny and systematics of sponges are to some extent still unresolved, and there is an on-going debate about the exact branching pattern of their main clades and their relationships to the other non-bilaterian animals. Here, we review the current state of the deep phylogeny of sponges. Several studies have suggested that sponges are paraphyletic. However, based on recent phylogenomic analyses, we suggest that the phylum Porifera could well be monophyletic, in accordance with cladistic analyses based on morphology. This finding has many implications for the evolutionary interpretation of early animal traits and sponge development. We further review the contribution that mitochondrial genes and genomes have made to sponge phylogenetics and explore the current state of the molecular phylogenies of the four main sponge lineages (Classes), that is, Demospongiae, Hexactinellida, Calcarea, and Homoscleromorpha, in detail. While classical systematic systems are largely congruent with molecular phylogenies in the class Hexactinellida and in certain parts of Demospongiae and Homoscleromorpha, the high degree of incongruence in the class Calcarea still represents a challenge. We highlight future areas of research to fill existing gaps in our knowledge. By reviewing sponge development in an evolutionary and phylogenetic context, we support previous suggestions that sponge larvae share traits and complexity with eumetazoans and that the simple sedentary adult lifestyle of sponges probably reflects some degree of secondary simplification. In summary, while deep sponge phylogenetics has made many advances in the past years, considerable efforts are still required to achieve a comprehensive understanding of the relationships among and within the main sponge lineages to fully appreciate the evolution of this extraordinary metazoan phylum.

Speculation with spiculation?—Three independent gene fragments and biochemical characters versus morphology in demosponge higher classification

Demosponge higher-level systematics is currently a subject of major changes due to the simplicity and paucity of complex morphological characters. Still, sponge classification is primarily based on morphological features. The systematics of the demosponge order Agelasida has been exceptionally problematic in the past. Here, we present the first molecular phylogenetic analysis based on three partially independent genes in demosponges in combination with a comprehensive search for biochemical synapomorphies to indicate their phylogenetic relationships. We show how sponges with fundamentally different skeletons can be in fact closely related and discuss examples of the misleading nature of morphological systematics in sponges.

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.