When performing the description of the animals, we always mention the issue of presence or absence of coelom. Based on this characteristic, the triblastic animals can be organized into three groups: coelomate, accolades or pseudocoelom. But, after all, what is coelom?
the coelom can be defined as a fluid-filled body cavity that has the lining of the mesoderm, one of the germinal leaflets. This cavity is formed during embryonic development and is related to several important functions, such as excreta elimination, deposition. gametes, distribution of substances throughout the body, accommodation of internal organs and, in some animals, it also works as a form of support (skeleton hydrostatic).
Animals that have these cavities are called coelomate. An example is all triblastic organisms, with the exception of the flatworms and nematodes. Note in the figure below that in coeloms the body cavity is completely lined with mesoderm.
Observe the arrangement of germinal leaflets in coelom, pseudocoelom and coelom organisms
There are still organisms pseudocoelom which have body cavities, however, these are only partially covered by the mesoderm. In the diagram above, it is possible to observe that the cavity is covered by mesoderm and endoderm. Representatives of the Nematoda phylum are examples of pseudocoelom animals.
Finally, we have the organisms called accolades, which do not have a body cavity surrounded by the mesoderm. In these animals, the space between the ectoderm and the endoderm is completely filled by the mesoderm. As an example, we can mention the flatworms.
Attention!Only triblastic animals can be classified according to the presence or absence of coelom. Therefore, cnidarians, which are diblastic, and the poriferous, which do not have brochures, cannot be classified according to this characteristic.
By Ma. Vanessa dos Santos
