The phylum Porifera comes under the category of Sponges. Normally in other animals the unspecialized cells are transformed into specialized cells whereas in sponges the specialized cells are transformed into some other types.
The body consists of jelly-like substance called mesohyl which is found in between the thin layer of cells. Sponges are not having nervous,digestive, excretory and circulatory system. Instead of those things they can maintain the constant water flow through their body in order to get the food, oxygen and also to remove the wastes from their body.
The shape of their body is not so fixed so that it can adapt the maximum efficiency of water flow. These species having their habitat in fresh water and also in the marine water to the depth of about 8,800 meters.
There are around 5,000-10,000 species in this variety. Most of the species take bacteria as their food as well as other food particles in the water. The sponges that live in the food scarcity area can become carnivorous and they mainly focus on small crustaceans.
The interesting feature with this species is that it can regenerate from their fragments that broken off from their body. Some other species can also reproduce by budding. The reproduction can takes place within the Porifera by means of sexual reproduction.
They can reproduce by releasing the sperm cells into the water. The other viviparous species can capture the sperm cells from the water; instead of digesting them they transform the sperm cells into the ova in the parent's mesohyl.
On the other hand the fertilized eggs started to develop in the parent. The larvae can then be released to find the suitable place to settle. Then in the oviparous species both the sperm and the egg cells are released in the water.
The fertilization can then take place outside the parent's body and started to develop there. Food particles with size above 50 micrometers cannot get into the ostia and pinacocytes. Asexual reproduction can take place in the Sponges by three methods like fragmentation, budding and by producing gemmules.
Fragments present in the body of the sponges may be detached either by currents of waves or by predators. Sponges are hermaphrodite that is both the male and female sexes are function simultaneously.
Though sponges have no reproductive organs the sperm cells are produced by the choanocytes while the eggs are produced by transforming archeocytes in some other species. The yolk can be consumed in the egg by the nurse cells. Sponges may start their sexual reproduction either in a few weeks old or it can wait until several years old.