The organisms which belong to phylum Porifera are multicellular and are also known as sponges. There are around 5,000 species that belong to this phylum. Amongst the different species, 900 belong to the freshwater sponges, while remaining are categorized as saltwater sponges.
The different features (structural and behavioral) of sponges make them an interesting topic for study. There are many different types of sponges found in nature. For the time-being, let us understand more about the characteristics of these organisms through this list:
- The body of organisms belonging to the phylum Porifera is hollow. It is made up of a jelly-like substance. Collagen forms an important component of the substance.
- The sponges are filter feeders, which means that they obtain food by filtering water. Pores on the body of these organisms prove to be useful in this.
- Body structure of the sponge is radially asymmetrical. Their body is formed of cells loosely connected to each other. These are not true tissues.
- Body of the sponges is divided in three layers. The outermost layer is formed of epidermal cells (flattened), semi-fluid matrix forms the middle layer, while collar cells form the innermost layer.
- There is an opening at the top of the body of sponges, which is known as osculum.
- Sponges are acoelomate, i.e., without a coelom.
- The adult sponges are sessile in nature, which means that they cannot move freely. The larvae of Poriferans are, however, motile. A ciliated body helps in movement of larvae.
- Plasticity of the body of sponges allows them to change their shape. We can, therefore, find them occupying irregular spaces on rocks and reefs.
- Being sessile in nature, the adult sponges need a substrate or surface to grow on. The substrate can be anything from skeletons, rocks, corals, to dead sponges.
- Sponges cannot exist without water. These organisms are, therefore, strictly aquatic.
- The Poriferans being filter feeders, it is interesting to know how their interaction with water takes place. Choanocytes, the flagellate cells, facilitate the movement of water currents through canals and chambers of the body.
- On an average, a Poriferan with a 10 cm body length can filter 100 liters of water everyday.
- Poriferans do not possess a digestive, nervous, or circulatory system.
- Reproduction in sponges takes place both sexually and asexually. The asexual reproduction takes place through gemmules or buds, while the sexual reproduction takes place by means of sperms and eggs.
- As stated above, the sponges are filter feeders. Bacterial plankton and other tiny particles are engulfed by these organisms to obtain food.
- The process of digesting food by sponges is termed as phagocytosis.
- Some of the sponges are not filter feeders. These are carnivorous in nature and feed on creatures like crustaceans.
- Some of the sponges have turned carnivorous because they live in areas with food-scarcity. Otherwise, the photosynthesizing microbes prove to be useful for organisms belonging to this phylum to derive food. These microbes live as endosymbionts in the body of sponges.
- There is an interesting feature about how the damaged tissues are repaired by sponges. The sponges, instead of regrowing damaged tissues, mobilize the adjoining cells in order to cover the wound.
- Immune system of the sponges is simple. The grafts (tissues) from organisms of other kinds are not accepted by them. However, they accept tissues from the organisms of the same species.
- Technically speaking, the sponges never suffer a natural death other than through dehydration or freezing.