In 1765 Ellis saw water currents in sponges and considered them animals. Linnaeus, Lamarck, and Cuuier placed the sponges in Zoophyta because they considered sponges to be related to anthozoan coelenterates. In 1816 "De Blainville" first stated that sponges do not show a relation with coelenterates. But in 19th-century sponges are placed with coelenterates only. In 1825 R.E. Gran* studied their morphology and physiology. Only 1836 RE. Grant- proposed the name "Porifera" and included the sponges in this group. In 1875 "Huxley" aid in 1884 "Sollas" separated the sponges from Metazoa. Sponges are now recognized as a separate group from Metazoa and named "Parazoa" af. ar "Sollas".
Sponges will not show tissue-grade organization. They will not show Cilia. The choanoderm will show choanocytes which are useful for bringing water currents into the body The development of the canal system, Ostia, oscula and spicules makes the sponges look more different from both Protozoa characters and other Metazoans. Hence they are placed in the "Parazoa" group.
Porifera is asymmetrical or symmetrical, multicellular animals. They show the cellular grade of the organization. They do not show organs. Mouth and specific nervous system are absent They show pores and canals. Through these structures water flows. Sponges show loose aggregation of cells. Tissue formation is absent. The body functions are performed by cells that are more or less independent. They show little cooperation.
Sponges are supported by an internal skeleton made of spicules. These spicules are made of calcium carbonate or silicon or spongin.
Sponges are sedentary. Many of them are confined to the marine environment. Only spongillidae family members are seen in freshwater, throughout the world.
They show great powers of regeneration. They show asexual and sexual methods of propagation. The sponges are of various shapes. They may be vase-like, branched, or globular. Many are brilliant red, orange, yellow, blue-violet, or black.
Today sponges have a wide variety of uses. Hence full-fledged sponge fishing' industry is producing over one thousand tons of sponges every year.