Porifera (Sponges): Recent Knowledge and New Perspectives

Abstract

Abstract Porifera, commonly named sponges, are devoid of head, digestive tract, nervous system, muscles or any other organs. Despite this anatomical and morphological simplicity, they are true animals or metazoans. Sponges are a successful group of mostly marine filter feeders that represent a major life form of several aquatic ecosystems. Efficient water filtration is performed by a network of pores (at the origin of their name), chambers and canals. Sponges are currently considered as one of the best candidates as sister group to all other animals; these organisms have therefore a key phylogenetic position. Recent studies have shown that they possess an unexpected molecular complexity raising exciting questions about early animal evolution. These results yielded an increased interest in the biology of these strange animals, and some sponge species can be considered as biological experimental models. Key Concepts As adults, sponges are sedentary filter feeder animals. The water flow is canalised in an aquiferous system composed of inhalant and exhalant pores (ostia and oscula), canals and choanocyte chambers. At present, the number of formally described sponge species is more than 9000. Sponges are divided into four clades (rank Class): Hexactinellida, Demospongiae, Calcarea and Homoscleromorpha. As sponges are devoid of organs, their individual cells or cell layers ensure vital functions. One cell type may have several functions. Sponges have high regeneration capabilities as well as a high capacity of cell transdifferentiation. Sponges often use both asexual and sexual reproduction. Most of the key transcription families and main signalling pathways required for other metazoans development and body patterning are present in sponges. The increasing interest for sponge biology improves our understanding of animal evolution and marine ecosystems.