Porifera

Sponges (Porifera) are morphologically simple, universally aquatic animals, with sessile adults and motile larvae. They are predominantly marine, with several genera occupying freshwater habitats, and are generally filter feeders (with some species secondarily carnivorous). The phylogenetic position of sponges—often considered to be the oldest of the surviving animal lineages—makes them the key phylum for comparative analyses aiming at understanding the origin of complex animal multicellularity. Sponge genomes contain plethora of regulatory genes governing development of complex animals. At the same time, sponges appear to have retained many characteristics of animal ancestors, including bacterivory, biphasic lifestyle and rather fluid cell identity. This last feature is likely linked with sponges’ spectacular ability to regenerate, including reorganization of complete bodies from dissociated cells, making sponges important models for regenerative biology studies. Because of their intimate association with various bacteria, sponges are also increasingly important as models for study of host-microbial interactions.