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.
