Porifera Characteristics

The organisms which belong to phylum Porifera are multicellular and are also known as sponges. The Poriferans are a diverse group; there are around 5,000 species included under this phylum. Amongst the different species, 900 belong to the freshwater sponges. Remaining species are categorized as saltwater Poriferans.

Phylum Porifera Characteristics

The different features (structural and behavioral) of the sponges makes 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 Poriferans (sponges) through this list:

• The body of sponges/Poriferans is hollow. It is made up of a jelly-like substance. Collagen forms an important component of the substance.
• The sponges are filter feeders. It means that they obtain food by filtering water; pores of the body prove to be useful in filtering water.
• Body structure of the sponge is radially asymmetrical. The body of Poriferans 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. Collar cells form the innermost layer of the body of Poriferans.
• There is an opening at the top of the body of sponges. This opening is known as osculum.
• These sponges are acoelomate i.e. without a coelom.
• The adult sponges are sessile in nature; it means they cannot move freely. The larvae of Poriferans are however, motile. A ciliated body helps in movement of larvae.
• Plasticity of the Poriferan body allows them to change their shape. We can therefore find the sponges 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 or dead sponges.
• The sponges cannot exist without water. These organisms are therefore, strictly aquatic.
• The Poriferans being filter feeders, it is interesting to know how the 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 10 cm body length can filter 100 liters of water everyday.
• The Poriferans do not possess a digestive, nervous or circulatory system.
• Reproduction in sponges takes place both by means of sexual and asexual reproduction. The asexual reproduction takes place through gemmules or buds. 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 Poriferans 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 Poriferans 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 the sponges. However, sponges accept tissues from the organisms of the same species.
• Technically speaking, the sponges never suffer a natural death other than through dehydration or freezing.

The different Porifera characteristics listed in this article should help understand about these organisms in detail. The sponges have survived and flourished in the aquatic environment owing to these features/characteristics.