You poriferous (Filo Porifera), also popularly known as sponges, are very simple animals that live exclusively in the aquatic environment. They don't have real tissues, so they don't have organs and systems either. They are sessile (do not move) and can live alone or in colonies. They have a body full of pores, hence the name porifers (from the Latin: porus = pore and iron = possessor).
Read too: Coral reefs, a place where you can see sponges
General characteristics of porifers
Porifers are very simple animals and do not have cells organized into real tissues, so these cells have a certain independence. These animals are sessiles and strainers, that is, they do not move and remove the particles necessary for their survival from the aquatic environment. Some species have a great capacity for regeneration.
They vary greatly in size, ranging from a few millimeters to several meters. They are usually asymmetric, but species with radial symmetry can be observed. They occur in both fresh and salt water; however, there are more marine species. There are more than
8000 different species of sponges described currently, which vary in color and shape.the body of porifers
The body of porifers is quite simple, but it is possible to observe different internal arrangements. Next, we will describe the simplest organization, the asconoid structure.
Sponges have a generally cylindrical body and are rich in pores. These are formed by a cell, which has a ring shape, called a porocyte. These pores serve as an entry point for the water, which goes to a central cavity. (spongiocele or atrium) and exits through a large opening, called the kiss. In the body of this animal, there is a constant stream of water.
The body of sponges consists of two layers of cells, which are separated by a gelatinous layer called mesoyl. The outer surface has flat cells, called the pinacocytes, which form the pinacoderm. These cells have the ability to expand and contract their margins, which can promote a small variation in the size of the animal.
The mesoyl appears as a gelatinous portion and it contains amoebocytes and skeletal material. You amoebocytes they move by means of pseudopods and help, among other functions, to transport nutrients to other cells and produce materials that will form the skeleton. The skeletal material, in turn, is formed by spicules and/or spongin fibers. The spikes have different shapes and sizes and can be formed by silica or limestone.
Facing the interior of the sponge, there is the presence of a layer of flagellate cells, called the choanocytes. These flagella are facing the interior of the spongiocele, and their agitation ensures the movement of water inside the animal's body and also the capture of food. Choanocytes have projections that form a sort of collar around the flagellum. For this reason, they are also called paste cells.
Types of sponges
The body of sponges has different organizations, and it is possible to observe three different structural types. Let's see a little more about these three types of sponges below:
- Asconoid or Ascon type: it is the simplest type, being observed a thin wall, perforated by pores, which open in the spongiocele. This opens at the osculum. Usually sponges with this structure tend to be small.
- Siconoid or Sicon type: they have a more complex body, with folds on the walls. In this group, choanocytes do not line the spongiocele, being observed in radial channels.
- Leuconoid or Leucon type: more complex type of sponge, showing a great degree of wrinkling of the body. It has several channels and, usually, the atrium disappears or is very reduced.
Read too:Reino Animalia – discover the organisms that are part of this group
Physiology of porifers
The porifers are animals that do not have organs and systems, thus, some fundamental processes for their survival are very different from other animals. Digestion, for example, does not take place in a digestive system. The choanocytes are responsible for removing the food needed for the sponge from the water, subsequently making the intracellular digestion. They can also transfer food to amoebocytes, which carry substances to other cells.
At gas exchange occur in all poriferous cells through diffusion. Concerning excretion, this also occurs in all cells, with nitrogenous products being released into the water.
Reproduction of porifers
Sponges can reproduce both asexually and sexual. With regardà sexual reproduction, it should be noted that most sponges are hermaphroditic, that is, the same individual is responsible for the production of male and female gametes. However, this production does not usually occur at the same time, with the production of one type of gamete being observed before the production of another, a condition called sequential hermaphroditism. This prevents self-fertilization from occurring.
Sponge gametes are not produced in specialized structures but are formed from choanocytes or amoebocytes. The male gametes are released into the water, and the current of water transports them to another individual who is producing a female gamete, which is inside the sponge body. The male gamete is picked up by a coanocyte, which transports it to the female gamete. After fertilization, a free, swimming larva forms, which can colonize an area far from the parent sponge. The larva then attaches to the substrate and develops into an adult, sessile sponge.
As for the asexual reproduction, two types can occur: budding and budding. In budding, buds form on the animal's body, which can detach from the mother sponge body or remain attached to it. In gemmulation, in turn, reproductive structures called gemmules are formed, which are formed by undifferentiated cells that have an envelope. The gemmules are able to remain at rest in unfavorable environments, giving rise to a new sponge when the ideal conditions arise.
See too: Invertebrates - group of animals of which the porifers are part
Economic importance of porifers
Porifers are animals of great commercial value. Some sponges, for example, produce compounds that have antibacterial and anti-inflammatory potential. Currently, several studies are also carried out to test compounds produced by these animals that have an important action against cancer cells. Let's not forget that, in the past, sponges were used for bathing. Today, however, synthetic sponges are used.
By Vanessa Sardinha dos Santos
Biology teacher
