Porifera (Sponges): Recent Knowledge and New Perspectives

Abstract

Abstract Porifera, commonly named sponges, are true animals or metazoan despite their anatomical and morphological simplicity that had led to a long‐time debate about their nature (animal versus vegetal) and constitution (colonies of unicellular organisms versus multicellular organisms). Sponges are a successful group of mostly marine filter feeder organisms that represent a major life form of several ecosystems. Devoid of organs, the main characteristics of their body plan are the presence of a network of pores (at the origin of their name), choanocyte chambers and canals devoted to water filtration and spicules (when present) allowing tissue physical support. Currently considered as the sister group to all the other animals, these organisms have a key phylogenetic position. Recent studies have shown that they possess an unexpected molecular complexity raising exciting questions about early animal evolution. Key Concepts: As adults, sponges are sedentary filter feeder animals. The water flow is canalised in an aquiferous system composed of pores (ostia), canals and choanocyte chambers. At present, the number of formally described sponge species is comprised between 8000 and 9000. Sponges are divided into four clades […] 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. In addition to cell plurifunctionality, the functional plasticity of sponges also relies on a high capacity of cell transdifferentiation. Sponges often use both asexual and sexual reproduction. Most of key transcription families and main signalling pathways required for eumetazoan development and body patterning are present in sponges. The recent rising interest for Porifera is expected to lead to a better understanding of animal evolution.