Sponges reproduce asexually by budding, fragmentation, and producing gemmules. Gemmules are packets of cells produced by freshwater sponges that are able to withstand the harsh conditions of winter. Sexual reproduction involves producing eggs and sperm at different times. This condition of having both male and female gonads is called monoecious, but the sexes are usually developed at different times. Marine sponges produce larval forms via sexual reproduction, which helps distribute the species to additional favorable habitats and incidentally contributes to the protein base of the marine plankton.
Sponges are a very ancient group that is remotely related to the metazoa.
While they have been called parazoa in the past, which indicated a parallel position, more recent evidence suggests they are a sister group to the Eumetozoa. The sponges are the first multicellular animals but do not have an organ structures. The Calcarea have spicules of calcium carbonate and have all three body designs. The Hexactinellida are the glass sponges with spicules of silica. They are usually found in deep water.