Simply constructed, multicellular organisms, which nourish by the filtration of sea water.

The cells of sponges are already more or less differentiated, e.g. into cells producing the sponge skeleton, into cells propelling the waterflow through the sponge channels and filtrating this water and into cells involved in reproduction. After sexual reproduction, mobile, free-living larvae are formed, who are finally becoming sessile at the bottom of the sea, forming new sponges.