Phylum Porifera are the lowest multicellular animals belonging to the kingdom Animalia.
The word “Porifera” mainly refers to the pore bearers or pore bearing species. Based on the embryological studies, sponges are proved as animals and are classified into a separate Phylum in animals
This phylum includes about 5000 species. Poriferans are pore-bearing first multicellular animals. The pores are known as Ostia
The poriferans have a spongy appearance and are therefore called sponges. They are attached to the substratum and do not move. They have the ability to absorb and withhold fluids.
They were initially regarded as plants due to their green colour and their symbiotic relationship with algae. Later, their life cycle and feeding system were discovered, and they were included in the animal kingdom
Characteristics of Phylum Porifera
Some of the important characteristics of phylum Porifera are mentioned below.
1. The cells of Poriferans are loosely organized.
2. They are mostly found in marine water. Only a few are found in freshwater.
3. They are either radially symmetrical or asymmetrical.
4. Their body is usually cylindrical.
5. The scleroblast secretes spicules while spongin fibres are secreted by spongioblasts.
6. They have no organs in their body.
7. They depict cellular grade of organization.
8. The body comprises numerous pores known as Ostia and osculum.
9. The central cavity is called spongocoel or atrium which opens to the outside through the osculum
10. They reproduce asexually by budding, and fragmentation.
11. The nutrition is holozoic.
12. They have neurosensory cells but are devoid of any specific nervous system.
13. They have the power to regenerate the lost parts.
14. The development is indirect and the cleavage is holoblastic.
15. The exchange of respiratory gases and nitrogenous wastes occurs by the process of diffusion.
