Demosponges class (Demospongiae) contains the vast majority (6,900 species - ~85%) of all sponge species currently living in our seas and oceans. The name of this class is derived from the Greek demos meaning person and spongia meaning sponge, that is to say the 'people's sponge' or the 'common sponge'. This name is due to the fact that all those sponges that do not belong to the group of the Calcarea, Hexactinellida or Homoscleromorpha, are considered demosponges, and therefore as a class they are a kind of tailor's box. As a consequence, a great morphological diversity exists within the demosponges. We are dealing with a mostly marine class, with the only exception of the species of the family Spongillidae, which inhabit very oxygenated fresh waters.

Demosponges may have spicules of a siliceous nature, or may lack them. Generally the spicules are complemented or even replaced by a spongin protein network. This spongin mesh, and the absence of siliceous spicules, has meant that some species have historically been used as bathing sponges, to the point of endangering certain species in certain areas due to pressure to collect them.

As previously mentioned, demosponges are a very heterogeneous class, both in terms of shape and coloring. We can find from species that are incrustatnt, to others whose bodies are tall and slender, or low and extensive, or even with fan, vase or spherical shapes. The only common characteristic within the demosponges is that their bodies adopt a leuconoid-type morphology, that is, they have a reduced atrial cavity, and therefore the appearance of these sponges is considerably solid. They can have more than one opening for the exit of filtered water.

There are more than 15 orders, comprising 88 families and more than 1000 genera.