Also known as spongios or sponges, porifers probably appeared about 1 billion years ago and are thought to have originated in single-celled and heterotrophic beings. They have a body full of pores – hence its name – and a spongy, soft and flexible appearance. These are commonly used as a bath sponge. They are predominantly marine, but there is a freshwater family: Spongillidae . They live fixed, isolated or in colonies, are filters with silica or limestone skeleton, but do not have a muscular or nervous system, and have no differentiation between organs.
As they have no digestive system, the digestion of the porifers takes place intracellularly. They feed on particles suspended in water, which enter the pores together with the water and fall into the atrium – the sponge’s internal cavity – and exit through the osculus, which is a larger opening. When they enter there, the particles can remain trapped in the choanocytes, which are flagellated cells that promote the movement and circulation of water in the atrium of the sponge. These phagocytes and partially digest the particles that are sent to the amebocytes, which make up mesogleia – gelatinous material that fills the body of sponges -. Amoebocytes, in turn, finish digestion and distribute throughout the body.
Porifers do not have a respiratory system, whose gas exchange occurs through diffusion.
The excretion of porifers occurs through diffusion, as well as their breathing.
Basically the movement of the porifers is made up of water, food and sperm. The path begins at the pores, where they enter, and ends at the osculus, where they exit through the movement of the flagella of the coanocytes.
The reproduction of these animals can take place in two ways: asexual and sexual. When asexual, it can be done in three ways:
- Sprouting: asexual reproduction by sprouting consists of the appearance of a sprout in the body of the sponge, which can come loose and give rise to the new individual.
- Fragmentation: through fragmentation, reproduction happens with the small fragments that are released giving rise to new individuals. This happens due to the regenerative capacity that sponges have.
- Gemulation: asexual reproduction by gemulation takes place in freshwater sponges. Inside the body of the sponge, buds are formed, which are resistance structures composed of undifferentiated cells and protected by a rigid envelope.
In another view, we have analyzed that most sponges are hermaphrodites. Sexual reproduction is formed through gametes, formed in cells called gonocytes and leave the sponge by the osculus, penetrating another sponge through the water stream that passes through the pores. In this way, the coanocytes are captured and transferred to the eggs – in the mesogleia – that promote fertilization. There will be an egg, and from it a free-living larva that comes out of the sponge and swims until it settles.