AN INTRODUCTION TO SPONGES (PORIFERA)
In 1765 Ellis saw water currents in sponges and considered them as animals. Linnaeus, Lamarck and Cuuier placed the sponges in Zoophyta because they considered sponges are related to anthozoan coelenterates. In 1816 "De Blainville" first stated that sponges do not show 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 separated group from Metazoa and named them "Parazoa" af.ar "Sollas".
Sponges will not show tissue grade organisation. They will not show Cilia. The choanoderm will show choanocytes which are useful for bringing water currents into the body The development of canal system, ostia, oscula and spicules makes the sponges look more different from both Protozoa characters and other Metazoans. Hence they are placed in "Parazoa" group.
Porifera are asymmetrical or symmetrical, multicellular animals. They show cellular grade of 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 which are more or less independent. They show little cooperation.
Sponges are supported by internal skeleton made by spicules. These spicules are made by calcium carbonate or silicon or spongin.
Sponges are sedentary. Many of them are confined to marine environment. Only spongillidae family members are seen in the fresh water, throughout the world.
They show great powers of regenerations. They show asexual and sexual methods of propagation. The sponges are of various shapes. They may be vase like, branched, 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.