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8.2. Porifera

Phylum Porifera or Spongiaria

The porifera or sponges are a group of aquatic invertebrate animals, sessile (they live fixed on the sandy or rocky bottom) and lack authentic tissues .

Most of the 9,000 species of sponges are marine, only about 150 live in fresh water.

They are called porifera because their body is shaped like a hollow sack, with walls perforated by an aquifer system of pores, channels, and chambers, through which water enters, filters it, and expels it through a large hole, called an osculum, which has in the upper part of your body. In this way, they are nourished by retaining the organic particles and the oxygen that the water carries . Choanocytes are the cells lining the internal cavity of the sponge that create the water current and filter food.

They are the simplest multicellular beings, without true tissues or organs. They are asymmetric or with radial symmetry.

They usually have a skeleton made up of calcareous, siliceous spicules or organic spongin fibers that give them consistency.

Its reproduction can be both asexual, by budding and fragmentation, and sexual, by means of ovules and spermatozoa. In many cases, individuals are hermaphrodites.

They differ from other animals in that their digestion is only intracellular, since they have neither a mouth nor a digestive system that breaks down food.

They are also the only animals that do not have a nervous system.

The best-known example of a poriferous would be the natural bath sponge (Spongia officinalis), of which we only use its spongin spicules .

Esponja de baño

By Guido Picchetti - ( [GFDL or CC-BY-SA-3.0], via Wikimedia Commons